Journal articles: 'Inbreeding load'

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Nagy, István, and Thi Anh Nguyen. "Characterizing and Eliminating the Inbreeding Load." Veterinary Sciences 11, no. 1 (December 22, 2023): 8. http://dx.doi.org/10.3390/vetsci11010008.

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The authors evaluated the relevant literature related to purging, which is the interaction between selection and inbreeding in which the population may eliminate its inbreeding load at least partially. According to the relevant literature, the inbreeding load and the process of purging were evaluated via pedigree methods based on ancestral inbreeding, the inbreeding–purging model, and expressed opportunity of purging, along with genomic methods. Most ancestral inbreeding-related studies were performed in zoos, where only a small proportion of the studied populations show signs of purging. The inbreeding–purging model was developed with Drosophila, and it was used to evaluate different zoo ungulates and Pannon white rabbits. Purging was detected in both studies. The expressed opportunity of purging was applied in Jersey cattle and Pannon white rabbits. In the Jersey cattle, it had an effect of 12.6% for fitness, while in the Pannon white rabbits, the inbreeding load was between 40% and 80% of its original value. The genomic studies also signalled purging, but they also made it clear that, contrary to the detected purging, the evaluated populations still suffered from inbreeding depression. Therefore, especially for domesticated animals, it can be concluded that deliberate inbreeding with the purpose of generating purging is not advocated.

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CHARLESWORTH, BRIAN. "The effect of synergistic epistasis on the inbreeding load." Genetical Research 71, no. 1 (February 1998): 85–89. http://dx.doi.org/10.1017/s0016672398003140.

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The magnitude of inbreeding depression in Drosophila melanogaster appears too large to be accounted for by mutational load with multiplicative fitness interactions among loci, if current estimates of mutation and selection parameters are valid. One possible explanation for this discrepancy is synergistic epistasis among the fitness effects of deleterious mutations. A simple model of the effect of synergistic epistasis on the inbreeding load is developed. This model is used to show that deleterious mutations could account for the Drosophila data on the effects of inbreeding on components of fitness such as viability.

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BATAILLON, THOMAS, and MARK KIRKPATRICK. "Inbreeding depression due to mildly deleterious mutations in finite populations: size does matter." Genetical Research 75, no. 1 (February 2000): 75–81. http://dx.doi.org/10.1017/s0016672399004048.

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We studied the effects of population size on the inbreeding depression and genetic load caused by deleterious mutations at a single locus. Analysis shows how the inbreeding depression decreases as population size becomes smaller and/or the rate of inbreeding increases. This pattern contrasts with that for the load, which increases as population size becomes smaller but decreases as inbreeding rate goes up. The depression and load both approach asymptotic limits when the population size becomes very large or very small. Numerical results show that the transition between the small and the large population regimes is quite rapid, and occurs largely over a range of population sizes that vary by a factor of 10. The effects of drift on inbreeding depression may bias some estimates of the genomic rate of deleterious mutation. These effects could also be important in the evolution of breeding systems in hermaphroditic organisms and in the conservation of endangered populations.

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Wang, Dongfeng, Hosein Salehian-Dehkordi, Langda Suo, and Fenghua Lv. "Impacts of Population Size and Domestication Process on Genetic Diversity and Genetic Load in Genus Ovis." Genes 14, no. 10 (October 23, 2023): 1977. http://dx.doi.org/10.3390/genes14101977.

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In theoretical biology, a prevailing hypothesis posits a profound interconnection between effective population size (Ne), genetic diversity, inbreeding, and genetic load. The domestication and improvement processes are believed to be pivotal in diminishing genetic diversity while elevating levels of inbreeding and increasing genetic load. In this study, we performed a whole genome analysis to quantity genetic diversity, inbreeding, and genetic load across seven wild Ovis species and five domesticated sheep breeds. Our research demonstrates that the genetic load and diversity of species in the genus Ovis have no discernible impact on recent Ne, and three species within the subgenus Pachyceros tend to carry a higher genetic load and lower genetic diversity patterns. The results coincide with these species’ dramatic decline in population sizes within the subgenus Pachyceros ~80–250 thousand years ago. European mouflon presented with the lowest Ne, lower genetic diversity, and higher individual inbreeding coefficient but a lower genetic load (missense and LoF). This suggests that the small Ne of European mouflon could reduce harmful mutations compared to other species within the genus Ovis. We showed lower genetic diversity in domesticated sheep than in Asiatic mouflon, but counterintuitive patterns of genetic load, i.e., lower weak genetic load (missense mutation) and no significant difference in strong genetic load (LoF mutation) between domestic sheep and Asiatic mouflon. These findings reveal that the “cost of domestication” during domestication and improvement processes reduced genetic diversity and purified weak genetic load more efficiently than wild species.

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Latter, B. D., J. C. Mulley, D. Reid, and L. Pascoe. "Reduced genetic load revealed by slow inbreeding in Drosophila melanogaster." Genetics 139, no. 1 (January 1, 1995): 287–97. http://dx.doi.org/10.1093/genetics/139.1.287.

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Abstract The rate of decline in reproductive fitness in populations of Drosophila melanogaster inbred at an initial rate of approximately 1% per generation has been investigated under both competitive and noncompetitive conditions. Breeding population size was variable in the inbred lines with an estimated harmonic mean of 66.7 +/- 2.2. Of the 60 lines maintained without reserves, 75% survived a period of 210 generations of slow inbreeding and were then rapidly inbred by full-sib mating to near-homozygosity. The initial rate of inbreeding was estimated to be 0.96 +/- 0.16% per generation, corresponding to an effective population size of approximately 50. However, the rate of inbreeding declined significantly with time to average only 0.52 +/- 0.08% per generation over the 210 generation period, most likely due to associative overdominance built up by genetic sampling and selection in the small populations. The total inbreeding depression in fitness was estimated to be 87 +/- 3% for competitive ability and 27 +/- 5% for fitness under uncrowded conditions, corresponding to rates of decline of 2.0 +/- 0.3 and 0.32 +/- 0.07%, respectively, per 1% increase in the inbreeding coefficient. The frequency of lethal second chromosomes in the resultant near-homozygous lines was of the order of 5%, lethal free second chromosomes showed a mean viability under both crowded and uncrowded conditions of approximately 95%, and their population cage fitness was 60% that of Cy/+ heterozygotes. It can be concluded that homozygous genotypes from which deleterious genes of major effect have been eliminated during slow inbreeding may show far less depression in reproductive fitness than suggested by earlier studies of wild chromosome homozygotes. The loss in fitness due to homozygosity throughout the entire genome may be as little as 85-90% under competitive conditions, and 25-30% in an optimal environment.

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Guillaume, Frédéric, and Nicolas Perrin. "Joint Evolution of Dispersal and Inbreeding Load." Genetics 173, no. 1 (March 1, 2006): 497–509. http://dx.doi.org/10.1534/genetics.105.046847.

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Nietlisbach, Pirmin, Stefanie Muff, Jane M. Reid, Michael C. Whitlock, and Lukas F. Keller. "Nonequivalent lethal equivalents: Models and inbreeding metrics for unbiased estimation of inbreeding load." Evolutionary Applications 12, no. 2 (October 23, 2018): 266–79. http://dx.doi.org/10.1111/eva.12713.

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Fox, C. W., K. L. Scheibly, B. P. Smith, and W. G. Wallin. "Inbreeding depression in two seed-feeding beetles, Callosobruchus maculatus and Stator limbatus (Coleoptera: Chrysomelidae)." Bulletin of Entomological Research 97, no. 1 (February 2007): 49–54. http://dx.doi.org/10.1017/s0007485307004737.

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AbstractInbreeding depression is well documented in insects but the degree to which inbreeding depression varies among populations within species, and among traits within populations, is poorly studied in insects other than Drosophila. Inbreeding depression was examined in two long-term laboratory colonies of the seed beetle, Callosobruchus maculatus (Fabricius), which are used frequently as models for experiments in ecology, evolution and behaviour. Inbreeding depression in these laboratory colonies are compared with one recently field-collected population of a different seed beetle, Stator limbatus Horn. Inbreeding reduced embryogenesis, egg hatch and larval survival in both species, such that eggs produced by sib matings were >17% less likely to produce an adult offspring. Inbred larvae also took 4–6% longer to develop to emergence in both species. Inbreeding depression varied among the measured traits but did not differ between the two populations of C. maculatus for any trait, despite the large geographic distance between source populations (western Africa vs. southern India). Inbreeding depression was similar in magnitude between C. maculatus and S. limbatus. This study demonstrates that these laboratory populations of C. maculatus harbour substantial genetic loads, similar to the genetic load of populations of S. limbatus recently collected from the field.

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Willis, John H. "Inbreeding Load, Average Dominance and the Mutation Rate for Mildly Deleterious Alleles in Mimulus guttatus." Genetics 153, no. 4 (December 1, 1999): 1885–98. http://dx.doi.org/10.1093/genetics/153.4.1885.

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Abstract The goal of this study is to provide information on the genetics of inbreeding depression in a primarily outcrossing population of Mimulus guttatus. Previous studies of this population indicate that there is tremendous inbreeding depression for nearly every fitness component and that almost all of this inbreeding depression is due to mildly deleterious alleles rather than recessive lethals or steriles. In this article I assayed the homozygous and heterozygous fitnesses of 184 highly inbred lines extracted from a natural population. Natural selection during the five generations of selfing involved in line formation essentially eliminated major deleterious alleles but was ineffective in purging alleles with minor fitness effects and did not appreciably diminish overall levels of inbreeding depression. Estimates of the average degree of dominance of these mildly deleterious alleles, obtained from the regression of heterozygous fitness on the sum of parental homozygous fitness, indicate that the detrimental alleles are partially recessive for most fitness traits, with h~∼0.15 for cumulative measures of fitness. The inbreeding load, B, for total fitness is ~1.0 in this experiment. These results are consistent with the hypothesis that spontaneous mildly deleterious mutations occur at a rate >0.1 mutation per genome per generation.

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ZHOU, SHU-RONG, and JOHN R. PANNELL. "Inbreeding depression and genetic load at partially linked loci in a metapopulation." Genetics Research 92, no. 2 (April 2010): 127–40. http://dx.doi.org/10.1017/s0016672310000133.

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SummaryInbreeding depression has important implications for a wide range of biological phenomena, such as inbreeding avoidance, the evolution and maintenance of sexual systems and extinction rates of small populations. Previous investigations have asked how inbreeding depression evolves in single and subdivided populations through the fixation of deleterious mutations as a result of drift, as well as through the expression of deleterious mutations segregating in a population. These studies have focused on the effects of mutation and selection at single loci, or at unlinked loci. Here, we used simulations to investigate the evolution of genetic load and inbreeding depression due to multiple partially linked loci in metapopulations. Our results indicate that the effect of linkage depends largely on the kinds of deleterious alleles involved. For weakly deleterious and partially recessive mutations, the speed of mutation accumulation at segregating loci in a random-mating subdivided population of a given structure tends to be retarded by increased recombination between adjacent loci – although the highest numbers of fixation of slightly recessive mutant alleles were for low but finite recombination rates. Although linkage had a relatively minor effect on the evolution of metapopulations unless very low values of recombination were assumed, close linkage between adjacent loci tended to enhance population structure and population turnover. Finally, within-deme inbreeding depression, between-deme inbreeding depression and heterosis generally increased with decreased recombination rates. Moreover, increased selfing reduced the effective amount of recombination, and hence the effects of tight linkage on metapopulation genetic structure were decreased with increasing selfing. In contrast, linkage had little effect on the fate of lethal and highly recessive alleles. We compare our simulation results with predictions made by models that ignore the complexities of recombination.

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Glémin, Sylvain, Thomas Bataillon, Joëlle Ronfort, Agnès Mignot, and Isabelle Olivieri. "Inbreeding Depression in Small Populations of Self-Incompatible Plants." Genetics 159, no. 3 (November 1, 2001): 1217–29. http://dx.doi.org/10.1093/genetics/159.3.1217.

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Abstract Self-incompatibility (SI) is a widespread mechanism that prevents inbreeding in flowering plants. In many species, SI is controlled by a single locus (the S locus) where numerous alleles are maintained by negative frequency-dependent selection. Inbreeding depression, the decline in fitness of selfed individuals compared to outcrossed ones, is an essential factor in the evolution of SI systems. Conversely, breeding systems influence levels of inbreeding depression. Little is known about the joint effect of SI and drift on inbreeding depression. Here we studied, using a two-locus model, the effect of SI (frequency-dependent selection) on a locus subject to recurrent deleterious mutations causing inbreeding depression. Simulations were performed to assess the effect of population size and linkage between the two loci on the level of inbreeding depression and genetic load. We show that the sheltering of deleterious alleles linked to the S locus strengthens inbreeding depression in small populations. We discuss the implications of our results for the evolution of SI systems.

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THEODOROU, KONSTANTINOS, and DENIS COUVET. "Inbreeding depression and heterosis in a subdivided population: influence of the mating system." Genetical Research 80, no. 2 (October 2002): 107–16. http://dx.doi.org/10.1017/s0016672302005785.

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We investigate the joint effects of gene flow and selfing on the level of inbreeding depression, heterosis and genetic load in a subdivided population at equilibrium. Low gene flow reduces inbreeding depression and substantially increases heterosis. However, in highly self-fertilizing populations, inbreeding depression is independent of the amount of gene flow. When migration occurs via pollen, consanguinity of the reproductive system could have a negative influence on subpopulation persistence, in contrast to the case of isolated populations. However, with only seed migration, genetic load and heterosis depend mildly on the mating system. From an evolutionary point of view, we reach two main conclusions: first, outcrossing is selected for if gene flow is low; second, intermediate levels of gene flow could promote mixed mating systems, especially when migration occurs through pollen.

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Pérez-Pereira, Noelia, Armando Caballero, and Aurora García-Dorado. "Reviewing the consequences of genetic purging on the success of rescue programs." Conservation Genetics 23, no. 1 (October 19, 2021): 1–17. http://dx.doi.org/10.1007/s10592-021-01405-7.

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AbstractGenetic rescue is increasingly considered a promising and underused conservation strategy to reduce inbreeding depression and restore genetic diversity in endangered populations, but the empirical evidence supporting its application is limited to a few generations. Here we discuss on the light of theory the role of inbreeding depression arising from partially recessive deleterious mutations and of genetic purging as main determinants of the medium to long-term success of rescue programs. This role depends on two main predictions: (1) The inbreeding load hidden in populations with a long stable demography increases with the effective population size; and (2) After a population shrinks, purging tends to remove its (partially) recessive deleterious alleles, a process that is slower but more efficient for large populations than for small ones. We also carry out computer simulations to investigate the impact of genetic purging on the medium to long term success of genetic rescue programs. For some scenarios, it is found that hybrid vigor followed by purging will lead to sustained successful rescue. However, there may be specific situations where the recipient population is so small that it cannot purge the inbreeding load introduced by migrants, which would lead to increased fitness inbreeding depression and extinction risk in the medium to long term. In such cases, the risk is expected to be higher if migrants came from a large non-purged population with high inbreeding load, particularly after the accumulation of the stochastic effects ascribed to repeated occasional migration events. Therefore, under the specific deleterious recessive mutation model considered, we conclude that additional caution should be taken in rescue programs. Unless the endangered population harbors some distinctive genetic singularity whose conservation is a main concern, restoration by continuous stable gene flow should be considered, whenever feasible, as it reduces the extinction risk compared to repeated occasional migration and can also allow recolonization events.

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Brekke, Patricia, Peter M. Bennett, Jinliang Wang, Nathalie Pettorelli, and John G. Ewen. "Sensitive males: inbreeding depression in an endangered bird." Proceedings of the Royal Society B: Biological Sciences 277, no. 1700 (June 30, 2010): 3677–84. http://dx.doi.org/10.1098/rspb.2010.1144.

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Attempts to conserve threatened species by establishing new populations via reintroduction are controversial. Theory predicts that genetic bottlenecks result in increased mating between relatives and inbreeding depression. However, few studies of wild sourced reintroductions have carefully examined these genetic consequences. Our study assesses inbreeding and inbreeding depression in a free-living reintroduced population of an endangered New Zealand bird, the hihi ( Notiomystis cincta ). Using molecular sexing and marker-based inbreeding coefficients estimated from 19 autosomal microsatellite loci, we show that (i) inbreeding depresses offspring survival, (ii) male embryos are more inbred on average than female embryos, (iii) the effect of inbreeding depression is male-biased and (iv) this population has a substantial genetic load. Male susceptibility to inbreeding during embryo and nestling development may be due to size dimorphism, resulting in faster growth rates and more stressful development for male embryos and nestlings compared with females. This work highlights the effects of inbreeding at early life-history stages and the repercussions for the long-term population viability of threatened species.

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Kövér, György, Ino Curik, Lubos Vostry, János Farkas, Dávid Mezőszentgyörgyi, and István Nagy. "Analysis of Inbreeding Effects on Survival at Birth of Pannon White Rabbits Using the Inbreeding-Purging Model." Diversity 15, no. 1 (January 6, 2023): 71. http://dx.doi.org/10.3390/d15010071.

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Mating between related animals is an inevitable consequence of a closed population structure especially when it coincides with a small population size. As a result, inbreeding depression may be encountered especially when considering fitness traits. However, under certain circumstances, the joint effects of inbreeding and selection may at least partly purge the detrimental genes from the population. In the course of this study, our objective was to determine the status of purging and to quantify the magnitude of the eliminated genetic load for the survival at birth of Pannon White rabbit kits maintained in a closed nucleus population. The evolution of the survival at birth was evaluated by applying the PurgeR R package based on the inbreeding-purging model. In the period from 1992 to 2017, 22.718 kindling records were analyzed. According to the heuristic approach, the purging coefficient reached the maximum possible value of 0.5 when estimating between 1992 and 1997. Based on the expected fitness over generations and on the expressed opportunity of purging, the beneficial effects of purging could be expected after 10 generations. The proportion of the purged genetic load could be between 20% and 60%. While the results obtained are not entirely conclusive, they do raise the possibility that some of the inbreeding load was caused, at least in part, by genes that could be successfully removed from the population by purging.

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Samayoa, Luis Fernando, Bode A. Olukolu, Chin Jian Yang, Qiuyue Chen, Markus G. Stetter, Alessandra M. York, Jose de Jesus Sanchez-Gonzalez, et al. "Domestication reshaped the genetic basis of inbreeding depression in a maize landrace compared to its wild relative, teosinte." PLOS Genetics 17, no. 12 (December 20, 2021): e1009797. http://dx.doi.org/10.1371/journal.pgen.1009797.

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Inbreeding depression is the reduction in fitness and vigor resulting from mating of close relatives observed in many plant and animal species. The extent to which the genetic load of mutations contributing to inbreeding depression is due to large-effect mutations versus variants with very small individual effects is unknown and may be affected by population history. We compared the effects of outcrossing and self-fertilization on 18 traits in a landrace population of maize, which underwent a population bottleneck during domestication, and a neighboring population of its wild relative teosinte. Inbreeding depression was greater in maize than teosinte for 15 of 18 traits, congruent with the greater segregating genetic load in the maize population that we predicted from sequence data. Parental breeding values were highly consistent between outcross and selfed offspring, indicating that additive effects determine most of the genetic value even in the presence of strong inbreeding depression. We developed a novel linkage scan to identify quantitative trait loci (QTL) representing large-effect rare variants carried by only a single parent, which were more important in teosinte than maize. Teosinte also carried more putative juvenile-acting lethal variants identified by segregation distortion. These results suggest a mixture of mostly polygenic, small-effect partially recessive effects in linkage disequilibrium underlying inbreeding depression, with an additional contribution from rare larger-effect variants that was more important in teosinte but depleted in maize following the domestication bottleneck. Purging associated with the maize domestication bottleneck may have selected against some large effect variants, but polygenic load is harder to purge and overall segregating mutational burden increased in maize compared to teosinte.

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Whitlock, Michael C. "Selection, Load and Inbreeding Depression in a Large Metapopulation." Genetics 160, no. 3 (March 1, 2002): 1191–202. http://dx.doi.org/10.1093/genetics/160.3.1191.

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Abstract The subdivision of a species into local populations causes its response to selection to change, even if selection is uniform across space. Population structure increases the frequency of homozygotes and therefore makes selection on homozygous effects more effective. However, population subdivision can increase the probability of competition among relatives, which may reduce the efficacy of selection. As a result, the response to selection can be either increased or decreased in a subdivided population relative to an undivided one, depending on the dominance coefficient FST and whether selection is hard or soft. Realistic levels of population structure tend to reduce the mean frequency of deleterious alleles. The mutation load tends to be decreased in a subdivided population for recessive alleles, as does the expected inbreeding depression. The magnitude of the effects of population subdivision tends to be greatest in species with hard selection rather than soft selection. Population structure can play an important role in determining the mean fitness of populations at equilibrium between mutation and selection.

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Agrawal, Aneil. "Understanding genetic variance, load, and inbreeding depression with selfing." Peer Community in Evolutionary Biology, no. 2 (November 18, 2017): 100041. http://dx.doi.org/10.24072/pci.evolbiol.100041.

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Casellas, J. "On individual-specific prediction of hidden inbreeding depression load." Journal of Animal Breeding and Genetics 135, no. 1 (December 11, 2017): 37–44. http://dx.doi.org/10.1111/jbg.12308.

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Charlesworth, Brian. "Mutational load, inbreeding depression and heterosis in subdivided populations." Molecular Ecology 27, no. 24 (December 2018): 4991–5003. http://dx.doi.org/10.1111/mec.14933.

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Mullin, Tim J., Torgny Persson, Sara Abrahamsson, and Bengt Andersson Gull. "Effects of inbreeding depression on seed production in Scots pine (Pinus sylvestris)." Canadian Journal of Forest Research 49, no. 7 (July 2019): 854–60. http://dx.doi.org/10.1139/cjfr-2019-0049.

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Like other outcrossing species, Scots pine (Pinus sylvestris L.) is thought to carry a “genetic load” of deleterious recessive alleles. When these alleles occur as homozygotes in inbred progeny, their expression can give rise to “inbreeding depression”. Although this phenomenon has been studied in several conifer species through selfing, few studies have quantified inbreeding depression in crosses with lower levels of relatedness between parents. We report here on the generation of a set of F3 study materials in Scots pine in which 142 families arose from a mating design among 49 F2 parents, representing nine levels of expected inbreeding coefficients between 0.0 and 0.5, and repeated over two consecutive seasons. Whereas the numbers of extractable seeds were unaffected by inbreeding, the proportion with fully developed embryos was strongly affected. This was expressed as inbreeding depression in the yield of full seeds per cone but not in their mean mass. Levels of germination of these full seeds were affected by inbreeding, but the depression was rather small and only weakly significant. The roles of pollen competition and polyembryony in mitigating the impact of inbreeding depression are discussed. The materials have been outplanted for future assessment of inbreeding depression on growth and survival.

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Willoughby, Janna R., Peter M. Waser, Anna Brüniche-Olsen, and Mark R. Christie. "Inbreeding load and inbreeding depression estimated from lifetime reproductive success in a small, dispersal-limited population." Heredity 123, no. 2 (February 26, 2019): 192–201. http://dx.doi.org/10.1038/s41437-019-0197-z.

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GLÉMIN, SYLVAIN. "Lethals in subdivided populations." Genetical Research 86, no. 1 (August 2005): 41–51. http://dx.doi.org/10.1017/s0016672305007676.

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The fate of lethal alleles in populations is of interest in evolutionary and conservation biology for several reasons. For instance, lethals may contribute substantially to inbreeding depression. The frequency of lethal alleles depends on population size, but it is not clear how it is affected by population structure. By analysing the case of the infinite island model by numerical approaches and analytical approximations it is shown that, like population size, population structure affects the fate of lethal alleles if dominance levels are low. Inbreeding depression caused by such alleles is also affected by the population structure, whereas the mutation load is only weakly affected. Heterosis also depends on population structure, but it always remains low, of the order of the mutation rate or less. These patterns are compared with those caused by mildly deleterious mutations to give a general picture of the effect of population structure on inbreeding depression, heterosis, and the mutation load.

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Kimbeng, C. A., and E. T. Bingham. "Population improvement in lucerne (Medicago sativa L.): components of inbreeding depression are different in original and improved populations." Australian Journal of Experimental Agriculture 38, no. 8 (1998): 831. http://dx.doi.org/10.1071/ea98112.

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Summary. Inbreeding depression, the lowered fitness of inbred individuals compared with their non-inbred counterparts, is an important concept in lucerne improvement; but is poorly understood. Two-allele autotetraploid populations are suitable for studying inbreeding depression, especially when the population improvement strategy involves inbreeding, because they are derived from chromosome-doubling of hybrid diploid plants. They have a maximum of 2 alleles and a single allelic interaction per locus. Inbreeding depression was compared in original 2-allele autotetraploid populations and populations that had undergone inbreeding and selection. The original and improved (selected) populations were produced by intercrossing 2 single-cross lines from the original and improved 2-allele autotetraploid populations respectively. Herbage yield of the S1 and intercrossed generations derived from these populations was evaluated in field trials at Arlington, Wisconsin, USA, and used to estimate inbreeding depression. Herbage yield of the S1 and intercrossed generations derived from the improved population were significantly (P<0.01) higher, by 13.3 and 24%, respectively, than those derived from the original population. Selection during inbreeding probably decreased the frequency of deleterious alleles and accumulated favourable alleles. Inbreeding depression values were higher in the improved compared with the original population. Genetic load of deleterious alleles may account for much of the inbreeding depression observed in the original population, whereas, in the improved population, loss of heterozygosity or non-additive gene interactions between favourable alleles on linked chromosome segments may account for the substantial inbreeding depression. Therefore, in a population improvement program, the causes of inbreeding depression seem to be more important than their estimated value.

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Ritland, Kermit. "Inferring the genetic basis of inbreeding depression in plants." Genome 39, no. 1 (February 1, 1996): 1–8. http://dx.doi.org/10.1139/g96-001.

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Recent progress in the genetic analysis of inbreeding depression in plants is reviewed. While the debate over the importance of genes of dominance versus overdominance effect continues, the scope of inferences has widened and now includes such facets as the interactions between genes, the relative abundance of major versus minor genes, life cycle stage expression, and mutation rates. The types of inferences are classified into the genomic, where many genes are characterized as an average, and the genic, where individual genes are characterized. Genomic inferences can be based upon natural levels of inbreeding depression, purging experiments, the comparison of individuals of differing F (e.g., prior inbreeding), and various crossing designs. Genic inferences mainly involve mapping and characterizing loci with genetic markers, involving either a single cross or, ideally, several crosses. Alternative statistical models for analyzing polymorphic loci causing inbreeding depression should be a fruitful problem for geneticists to pursue. Key words : inbreeding depression, genetic load, self-fertilization, QTL mapping.

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Ferdy, Jean-Baptiste, Sandrine Loriot, Michel Sandmeier, Madeleine Lefranc, and Christian Raquin. "Inbreeding depression in a rare deceptive orchid." Canadian Journal of Botany 79, no. 10 (October 1, 2001): 1181–88. http://dx.doi.org/10.1139/b01-096.

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We quantified inbreeding depression for seed maturation and germination in a deceptively pollinated orchid (Dactylorhiza praetermissa (Druce) Soó). Deceptive species do not provide any reward to their pollinators, which thus visit few flowers per plant. Therefore, deceptive species are predicted to experience high outcrossing. In agreement with the prediction that species with high outcrossing rate should possess a heavy genetic load, we demonstrated inbreeding depression in one of the populations we studied. More surprisingly, we found some evidence of inbreeding depression at a small geographic scale. This was not expected, as deceptive orchids generally disperse their pollen and their seeds over long distances. We also demonstrated that the position of a flower within an inflorescence interacts with the type of cross. This indicates that resource availability might modify how severely deleterious mutations affect reproductive success. This could also explain why the intensity of inbreeding depression seems, in the populations we studied, to be determined more by environmental factors than by inbreeding level, as estimated from molecular markers. Inferences in terms of conservation biology are drawn from these results.Key words: inbreeding depression, deceptive pollination, orchid, Dactylorhiza praetermissa.

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SCHEIDEL, W. "BROTHER-SISTER MARRIAGE IN ROMAN EGYPT." Journal of Biosocial Science 29, no. 3 (July 1997): 361–71. http://dx.doi.org/10.1017/s0021932097003611.

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According to official census returns from Roman Egypt (first to third centuries CE) preserved on papyrus, 23·5% of all documented marriages in the Arsinoites district in the Fayum (n=102) were between brothers and sisters. In the second century CE, the rates were 37% in the city of Arsinoe and 18·9% in the surrounding villages. Documented pedigrees suggest a minimum mean level of inbreeding equivalent to a coefficient of inbreeding of 0·0975 in second century CE Arsinoe. Undocumented sources of inbreeding and an estimate based on the frequency of close-kin unions (corrected downwards to 30% for Arsinoe) indicate a mean coefficient of inbreeding of F=0·15-0·20 in Arsinoe and of F=0·10-0·15 in the villages at the end of the second century CE. These values are several times as high as any other documented levels of inbreeding. A schematic estimate of inbreeding depression in the offspring of full sibling couples indicates that fertility in these families had to be 20-50% above average to attain reproduction at replacement level. In the absence of information on the amount of genetic load in this population, this estimate may be too high

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Hughes, Kimberly A. "The inbreeding decline and average dominance of genes affecting male life-history characters in Drosophila melanogaster." Genetical Research 65, no. 1 (February 1995): 41–52. http://dx.doi.org/10.1017/s0016672300032997.

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SummaryThis paper describes the results of assays of male life-history characters in a large outbred laboratory population of D. melanogaster. Lines of flies homozygous for the entire third chromosome and lines of flies carrying two different third chromosomes were assayed for agespecific male mating ability (MMA), age-specific survivorship, male fertility, and body mass. The results of these assays were used to calculate the inbreeding decline associated with each of these traits, the average dominance of deleterious alleles that affect the traits, the genotypic and environmental components of variance for the homozygous lines, and phenotypic and genotypic correlations among the characters. Significant inbreeding decline was found for all characters except the Gompertz intercept and fertility. Early and late MMA show larger effects of inbreeding than any other trait. The inbreeding load for MMA is about the same magnitude as that for egg-to-adult viability, but is substantially less than that associated with total fitness. The estimated inbreeding decline and average dominance of male life-history characters are comparable to estimates for other Drosophila fitness components.

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Launey, Sophie, and Dennis Hedgecock. "High Genetic Load in the Pacific Oyster Crassostrea gigas." Genetics 159, no. 1 (September 1, 2001): 255–65. http://dx.doi.org/10.1093/genetics/159.1.255.

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Abstract The causes of inbreeding depression and the converse phenomenon of heterosis or hybrid vigor remain poorly understood despite their scientific and agricultural importance. In bivalve molluscs, related phenomena, marker-associated heterosis and distortion of marker segregation ratios, have been widely reported over the past 25 years. A large load of deleterious recessive mutations could explain both phenomena, according to the dominance hypothesis of heterosis. Using inbred lines derived from a natural population of Pacific oysters and classical crossbreeding experiments, we compare the segregation ratios of microsatellite DNA markers at 6 hr and 2–3 months postfertilization in F2 or F3 hybrid families. We find evidence for strong and widespread selection against identical-by-descent marker homozygotes. The marker segregation data, when fit to models of selection against linked deleterious recessive mutations and extrapolated to the whole genome, suggest that the wild founders of inbred lines carried a minimum of 8–14 highly deleterious recessive mutations. This evidence for a high genetic load strongly supports the dominance theory of heterosis and inbreeding depression and establishes the oyster as an animal model for understanding the genetic and physiological causes of these economically important phenomena.

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Wang, Jinliang, and William G. Hill. "Effect of Selection Against Deleterious Mutations on the Decline in Heterozygosity at Neutral Loci in Closely Inbreeding Populations." Genetics 153, no. 3 (November 1, 1999): 1475–89. http://dx.doi.org/10.1093/genetics/153.3.1475.

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Abstract Transition matrices for selfing and full-sib mating were derived to investigate the effect of selection against deleterious mutations on the process of inbreeding at a linked neutral locus. Selection was allowed to act within lines only (selection type I) or equally within and between lines (type II). For selfing lines under selection type I, inbreeding is always retarded, the retardation being determined by the recombination fraction between the neutral and selected loci and the inbreeding depression from the selected locus, irrespective of the selection coefficient (s) and dominance coefficient (h) of the mutant allele. For selfing under selection type II or full-sib mating under both selection types, inbreeding is delayed by weak selection (small s and sh), due to the associative overdominance created at the neutral locus, and accelerated by strong selection, due to the elevated differential contributions between alternative alleles at the neutral locus within individuals and between lines (for selection type II). For multiple fitness loci under selection, stochastic simulations were run for populations with selfing, full-sib mating, and random mating, using empirical estimates of mutation parameters and inbreeding load in Drosophila. The simulations results are in general compatible with empirical observations.

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WANG, JINLIANG, WILLIAM G. HILL, DEBORAH CHARLESWORTH, and BRIAN CHARLESWORTH. "Dynamics of inbreeding depression due to deleterious mutations in small populations: mutation parameters and inbreeding rate." Genetical Research 74, no. 2 (October 1999): 165–78. http://dx.doi.org/10.1017/s0016672399003900.

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A multilocus stochastic model is developed to simulate the dynamics of mutational load in small populations of various sizes. Old mutations sampled from a large ancestral population at mutation–selection balance and new mutations arising each generation are considered jointly, using biologically plausible lethal and deleterious mutation parameters. The results show that inbreeding depression and the number of lethal equivalents due to partially recessive mutations can be partly purged from the population by inbreeding, and that this purging mainly involves lethals or detrimentals of large effect. However, fitness decreases continuously with inbreeding, due to increased fixation and homozygosity of mildly deleterious mutants, resulting in extinctions of very small populations with low reproductive rates. No optimum inbreeding rate or population size exists for purging with respect to fitness (viability) changes, but there is an optimum inbreeding rate at a given final level of inbreeding for reducing inbreeding depression or the number of lethal equivalents. The interaction between selection against partially recessive mutations and genetic drift in small populations also influences the rate of decay of neutral variation. Weak selection against mutants relative to genetic drift results in apparent overdominance and thus an increase in effective size (Ne) at neutral loci, and strong selection relative to drift leads to a decrease in Ne due to the increased variance in family size. The simulation results and their implications are discussed in the context of biological conservation and tests for purging.

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RONFORT, J. "The mutation load under tetrasomic inheritance and its consequences for the evolution of the selfing rate in autotetraploid species." Genetical Research 74, no. 1 (August 1999): 31–42. http://dx.doi.org/10.1017/s0016672399003845.

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Single-locus equilibrium frequencies of a partially recessive deleterious mutation under the mutation–selection balance model are derived for partially selfing autotetraploid populations. Assuming multiplicative fitness interactions among loci, approximate solutions for the mean fitness and inbreeding depression values are also derived for the multiple locus case and compared with expectations for the diploid model. As in diploids, purging of deleterious mutations through consanguineous matings occurs in autotetraploid populations, i.e. the equilibrium mutation load is a decreasing function of the selfing rate. However, the variation of inbreeding depression with the selfing rate depends strongly on the dominance coefficients associated with the three heterozygous genotypes. Inbreeding depression can either increase or decrease with the selfing rate, and does not always vary monotonically. Expected issues for the evolution of the selfing rate consequently differ depending on the dominance coefficients. In some cases, expectations for the evolution of the selfing rate resemble expectations in diploids; but particular sets of dominance coefficients can be found that lead to either complete selfing or intermediate selfing rates as unique evolutionary stable state.

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Carr, David E., and Michele R. Dudash. "Recent approaches into the genetic basis of inbreeding depression in plants." Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 358, no. 1434 (June 29, 2003): 1071–84. http://dx.doi.org/10.1098/rstb.2003.1295.

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Predictions for the evolution of mating systems and genetic load vary, depending on the genetic basis of inbreeding depression (dominance versus overdominance, epistasis and the relative frequencies of genes of large and small effect). A distinction between the dominance and overdominance hypotheses is that deleterious recessive mutations should be purged in inbreeding populations. Comparative studies of populations differing in their level of inbreeding and experimental approaches that allow selection among inbred lines support this prediction. More direct biometric approaches provide strong support for the importance of partly recessive deleterious alleles. Investigators using molecular markers to study quantitative trait loci (QTL) often find support for overdominance, though pseudo–overdominance (deleterious alleles linked in repulsion) may bias this perception. QTL and biometric studies of inbred lines often find evidence for epistasis, which may also contribute to the perception of overdominance, though this may be because of the divergent lines initially crossed in QTL studies. Studies of marker segregation distortion commonly uncover genes of major effect on viability, but these have only minor contributions to inbreeding depression. Although considerable progress has been made in understanding the genetic basis of inbreeding depression, we feel that all three aspects merit more study in natural plant populations.

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Rao, P. Mohan, M. Ramesh, K. Geetha Kumari, and G. Sudhakar. "Consanguinity, inbreeding and genetic load in salis: A sub divided population of Andhra Pradesh, South India." Asian Pacific Journal of Health Sciences 4, no. 1 (March 30, 2017): 183–89. http://dx.doi.org/10.21276/apjhs.2017.4.1.29.

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35

Sivakumaran, T. A., and S. Karthikeyan. "Effects of Inbreeding on Reproductive Losses in Kota Tribe." Acta geneticae medicae et gemellologiae: twin research 46, no. 02 (April 1997): 123–28. http://dx.doi.org/10.1017/s0001566000000672.

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AbstractSanghvi's hypothesis on long term effects of inbreeding was tested in Kotas. Kota is a numerically small tribal population in the Nilgiri district, Tamil Nadu State, India. Consanguineous marriages are common in this tribe. A total of 95 couples were taken for this study and necessary data were collected on a set proforma. Of the 95 couples, 28 (29.5%) were consanguineously related. The inbreeding coefficient for autosomal genes is 0.022 and for sex-linked genes is 0.03. Inbreeding effects on reproductive losses were examined through an exponential regression model. Although the regression coefficient B values are positive, they are insignificant, suggesting no consistent relationship between degree of consanguinity and the reproductive losses. The estimates of genetic load is 1.8 lethal equivalents per gamete and the average B/A ratio is 5. These findings empirically support the Sanghvi's contention.

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36

Charlesworth, D., M. T. Morgan, and B. Charlesworth. "The effect of linkage and population size on inbreeding depression due to mutational load." Genetical Research 59, no. 1 (February 1992): 49–61. http://dx.doi.org/10.1017/s0016672300030160.

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SummaryUsing a stochastic model of a finite population in which there is mutation to partially recessive detrimental alleles at many loci, we study the effects of population size and linkage between the loci on the population mean fitness and inbreeding depression values. Although linkage between the selected loci decreases the amount of inbreeding depression, neither population size nor recombination rate have strong effects on these quantities, unless extremely small values are assumed. We also investigate how partial linkage between the loci that determine fitness affects the invasion of populations by alleles at a modifier locus that controls the selfing rate. In most of the cases studied, the direction of selection on modifiers was consistent with that found in our previous deterministic calculations. However, there was some evidence that linkage between the modifier locus and the selected loci makes outcrossing less likely to evolve; more losses of alleles promoting outcrossing occurred in runs with linkage than in runs with free recombination. We also studied the fate of neutral alleles introduced into populations carrying detrimental mutations. The times to loss of neutral alleles introduced at low frequency were shorter than those predicted for alleles in the absence of selected loci, taking into account the reduction of the effective population size due to inbreeding. Previous studies have been confined to outbreeding populations, and to alleles at frequencies close to one-half, and have found an effect in the opposite direction. It therefore appears that associations between neutral and selected loci may produce effects that differ according to the initial frequencies of the neutral alleles.

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37

Spigler, Rachel B., Konstantinos Theodorou, and Shu-Mei Chang. "Inbreeding depression and drift load in small populations at demographic disequilibrium." Evolution 71, no. 1 (November 16, 2016): 81–94. http://dx.doi.org/10.1111/evo.13103.

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38

ZHOU, SHURONG, CUICUI ZHOU, and JOHN R. PANNELL. "Genetic load, inbreeding depression and heterosis in an age-structured metapopulation." Journal of Evolutionary Biology 23, no. 11 (September 6, 2010): 2324–32. http://dx.doi.org/10.1111/j.1420-9101.2010.02091.x.

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39

Guillaume, Frédéric, and Nicolas Perrin. "Inbreeding Load, Bet Hedging, and the Evolution of Sex‐Biased Dispersal." American Naturalist 173, no. 4 (April 2009): 536–41. http://dx.doi.org/10.1086/597218.

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40

Agrawal, Aneil F. "Ecological Determinants of Mutation Load and Inbreeding Depression in Subdivided Populations." American Naturalist 176, no. 2 (August 2010): 111–22. http://dx.doi.org/10.1086/653672.

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41

Pekkala, Nina, K. Emily Knott, Janne S. Kotiaho, and Mikael Puurtinen. "Inbreeding rate modifies the dynamics of genetic load in small populations." Ecology and Evolution 2, no. 8 (July 1, 2012): 1791–804. http://dx.doi.org/10.1002/ece3.293.

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42

Ronfort, J., and D. Couvet. "A stochastic model of selection on selfing rates in structured populations." Genetical Research 65, no. 3 (June 1995): 209–22. http://dx.doi.org/10.1017/s0016672300033280.

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SummaryPrevious theoretical studies of the evolution of the selfing rate have shown that mixed mating systems are not evolutionary stable states. Such models have, however, not included the effects of population structure and thus biparental inbreeding together with the evolution of selfing rates and inbreeding depression. In order to examine selection on selfing rates in structured populations, a stochastic model simulating a finite population with partial selfing and restricted pollen and seed dispersal has been developed. Selection on the mating system was followed by introducing modifiers affecting the selfing rate. The major result was that, with density dependent recruitment, a process which maintains the population structure necessary for biparental inbreeding to occur, a mixed mating system could be maintained. This result was associated with an increase of the mutation load with high selfing rates, and the selected selfing rate depended on the degree of population structure rather than on the initial selfing rate. With low dominance of deleterious alleles, complete allogamy can be selected for. Further studies showed that the more general condition of spatial heterogeneity of recruitment can lead to similar results, the most important condition being the maintenance of genetic structure within populations. A brief survey of the empirical literature shows that a positive relationship between the magnitude of inbreeding depression and the inbreeding coefficient within populations has been observed, in support of the present model.

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43

López-Cortegano, Eugenio, Eulalia Moreno, and Aurora García-Dorado. "Genetic purging in captive endangered ungulates with extremely low effective population sizes." Heredity 127, no. 5 (September 28, 2021): 433–42. http://dx.doi.org/10.1038/s41437-021-00473-2.

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AbstractInbreeding threatens the survival of small populations by producing inbreeding depression, but also exposes recessive deleterious effects in homozygosis allowing for genetic purging. Using inbreeding-purging theory, we analyze early survival in four pedigreed captive breeding programs of endangered ungulates where population growth was prioritized so that most adult females were allowed to contribute offspring according to their fitness. We find evidence that purging can substantially reduce inbreeding depression in Gazella cuvieri (with effective population size Ne = 14) and Nanger dama (Ne = 11). No purging is detected in Ammotragus lervia (Ne = 4), in agreement with the notion that drift overcomes purging under fast inbreeding, nor in G. dorcas (Ne = 39) where, due to the larger population size, purging is slower and detection is expected to require more generations. Thus, although smaller populations are always expected to show smaller fitness (as well as less adaptive potential) than larger ones due to higher homozygosis and deleterious fixation, our results show that a substantial fraction of their inbreeding load and inbreeding depression can be purged when breeding contributions are governed by natural selection. Since management strategies intended to maximize the ratio from the effective to the actual population size tend to reduce purging, the search for a compromise between these strategies and purging could be beneficial in the long term. This could be achieved either by allowing some level of random mating and some role of natural selection in determining breeding contributions, or by undertaking reintroductions into the wild at the earliest opportunity.

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44

Llaurens, Violaine, Lucy Gonthier, and Sylvain Billiard. "The Sheltered Genetic Load Linked to the S Locus in Plants: New Insights From Theoretical and Empirical Approaches in Sporophytic Self-Incompatibility." Genetics 183, no. 3 (September 14, 2009): 1105–18. http://dx.doi.org/10.1534/genetics.109.102707.

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Inbreeding depression and mating systems evolution are closely linked, because the purging of deleterious mutations and the fitness of individuals may depend on outcrossing vs. selfing rates. Further, the accumulation of deleterious mutations may vary among genomic regions, especially for genes closely linked to loci under balancing selection. Sporophytic self-incompatibility (SSI) is a common genetic mechanism in angiosperm that enables hermaphrodite plants to avoid selfing and promote outcrossing. The SSI phenotype is determined by the S locus and may depend on dominance relationships among alleles. Since most individuals are heterozygous at the S locus and recombination is suppressed in the S-locus region, it has been suggested that deleterious mutations could accumulate at genes linked to the S locus, generating a “sheltered load.” In this article, we first theoretically investigate the conditions generating sheltered load in SSI. We show that deleterious mutations can accumulate in linkage with specific S alleles, and particularly if those S alleles are dominant. Second, we looked for the presence of sheltered load in Arabidopsis halleri using CO2 gas treatment to overcome self-incompatibility. By examining the segregation of S alleles and measuring the relative fitness of progeny, we found significant sheltered load associated with the most dominant S allele (S15) of three S alleles tested. This sheltered load seems to be expressed at several stages of the life cycle and to have a larger effect than genomic inbreeding depression.

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45

Glémin, Sylvain, Joëlle Ronfort, and Thomas Bataillon. "Patterns of Inbreeding Depression and Architecture of the Load in Subdivided Populations." Genetics 165, no. 4 (December 1, 2003): 2193–212. http://dx.doi.org/10.1093/genetics/165.4.2193.

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AbstractInbreeding depression is a general phenomenon that is due mainly to recessive deleterious mutations, the so-called mutation load. It has been much studied theoretically. However, until very recently, population structure has not been taken into account, even though it can be an important factor in the evolution of populations. Population subdivision modifies the dynamics of deleterious mutations because the outcome of selection depends on processes both within populations (selection and drift) and between populations (migration). Here, we present a general model that permits us to gain insight into patterns of inbreeding depression, heterosis, and the load in subdivided populations. We show that they can be interpreted with reference to single-population theory, using an appropriate local effective population size that integrates the effects of drift, selection, and migration. We term this the “effective population size of selection” (NeS). For the infinite island model, for example, it is equal to NeS=N(1+m∕hs), where N is the local population size, m the migration rate, and h and s the dominance and selection coefficients of deleterious mutation. Our results have implications for the estimation and interpretation of inbreeding depression in subdivided populations, especially regarding conservation issues. We also discuss the possible effects of migration and subdivision on the evolution of mating systems.

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Mamedova, R. A., E. K. Ginter, I. S. Moshkina, V. A. Galkina, and G. I. Elchinova. "Hereditary autosomal recessive pathology and its connection with inbreeding in Mari El Republic." Kazan medical journal 77, no. 4 (August 15, 1996): 241–43. http://dx.doi.org/10.17816/kazmj104501.

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The complex medical and population genetic stu dy is performed in 5 districts of Mari El Republic (Gornomarisky, Orshansky, Morkinsky, Sovetsky). The units of autosomal recessive pathology are found in 115 families with 137 patients. The high level of dependence of the load of autosomal recessive pathology on inbreeding is shown.

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Waller, Donald M. "Addressing Darwin's dilemma: Can pseudo‐overdominance explain persistent inbreeding depression and load?" Evolution 75, no. 4 (February 27, 2021): 779–93. http://dx.doi.org/10.1111/evo.14189.

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48

Kirkpatrick and Jarne. "The Effects of a Bottleneck on Inbreeding Depression and the Genetic Load." American Naturalist 155, no. 2 (2000): 154. http://dx.doi.org/10.2307/3078940.

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van Oosterhout, Cock, Wilte G. Zulstra, Marianne K. van Heuven, and Paul M. Brakefield. "INBREEDING DEPRESSION AND GENETIC LOAD IN LABORATORY METAPOPULATIONS OF THE BUTTERFLYBICYCLUS ANYNANA." Evolution 54, no. 1 (February 2000): 218–25. http://dx.doi.org/10.1111/j.0014-3820.2000.tb00022.x.

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Kirkpatrick, Mark, and Philippe Jarne. "The Effects of a Bottleneck on Inbreeding Depression and the Genetic Load." American Naturalist 155, no. 2 (February 2000): 154–67. http://dx.doi.org/10.1086/303312.

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Journal articles on the topic 'Inbreeding load'

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