scholarly journals POPULATION SIZE AND THE NATURE OF GENETIC LOAD IN GENTIANELLA GERMANICA

Evolution ◽  
2003 ◽  
Vol 57 (10) ◽  
pp. 2242-2251 ◽  
Author(s):  
Susanne Paland ◽  
Bernhard Schmid
Keyword(s):  
Population Size ◽  
Genetic Load ◽  
Gentianella Germanica

POPULATION SIZE AND THE NATURE OF GENETIC LOAD IN GENTIANELLA GERMANICA

Evolution ◽  
2003 ◽  
Vol 57 (10) ◽  
pp. 2242 ◽  
Author(s):  
Susanne Paland ◽  
Bernhard Schmid
Keyword(s):  
Population Size ◽  
Genetic Load ◽  
Gentianella Germanica

scholarly journals Inbreeding depression due to mildly deleterious mutations in finite populations: size does matter

2000 ◽  
Vol 75 (1) ◽  
pp. 75-81 ◽  
Author(s):  
THOMAS BATAILLON ◽  
MARK KIRKPATRICK
Keyword(s):  
Population Size ◽  
Inbreeding Depression ◽  
Deleterious Mutation ◽  
Large Population ◽  
Genetic Load ◽  
Breeding Systems ◽  
Deleterious Mutations ◽  
Single Locus Analysis ◽  
Population Sizes ◽  
Inbreeding Rate

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.

scholarly journals Population history and the differential consequences of inbreeding and outcrossing in a plant metapoplation

2020 ◽  
Author(s):  
Peter D. Fields ◽  
Gretchen Arnold ◽  
Joel M. Kniskern ◽  
Douglas R. Taylor
Keyword(s):  
Gene Flow ◽  
Population Size ◽  
Empirical Studies ◽  
Genetic Load ◽  
Population History ◽  
Silene Latifolia ◽  
Population Genetic Analysis ◽  
Crossing Experiment ◽  
Estimate Gene Flow ◽  
Historical Variation

ABSTRACTThe phenotypic consequences of inbreeding typically result in a fitness decline proportional to the increase in the inbreeding coefficient, F. This basic assumption of a predictable, inverse relationship between fitness and F has been questioned by a number of empirical studies. We explored the relationship between population history and inbreeding in a metapopulation of the plant Silene latifolia, for which long-term data are available for the historical size and spatial distribution of hundreds of local demes. We used a population genetic analysis to estimate gene flow and bi-parental inbreeding (FIS) in demes with different histories of spatial isolation. A controlled crossing experiment examined whether the effect of inbreeding and outcrossing on fitness-related traits varied with different histories of population size and isolation. Historically isolated demes experienced less gene flow and an increase in FIS, as well as significant inbreeding advantage and outbreeding depression for traits expressed early in life. The causes of variation in the F-fitness relationship among populations will include variance in the distribution of deleterious recessive alleles driven by aspects of population history, including population size, founder effects, gene flow, bi-parental inbreeding, and opportunities for the purging of genetic load. Our findings show that isolation and historical variation in population size likely contribute substantial variation in past inbreeding and the consequences of future inbreeding across the metapopulation.

scholarly journals Genetic Diversity, Inbreeding Level, and Genetic Load in Endangered Snub-Nosed Monkeys (Rhinopithecus)

2020 ◽  
Vol 11 ◽  
Author(s):  
Weimin Kuang ◽  
Jingyang Hu ◽  
Hong Wu ◽  
Xiaotian Fen ◽  
Qingyan Dai ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Population Size ◽  
Large Population ◽  
Population Decline ◽  
Genetic Load ◽  
Term Survival ◽  
Population Sizes ◽  
Genomic Inbreeding ◽  
Inbreeding Level

The snub-nosed monkey genus (Rhinopithecus) comprises five closely related species (R. avunculus, R. bieti, R. brelichi, R. roxellana, and R. strykeri). All are among the world's rarest and most endangered primates. However, the genomic impact associated with their population decline remains unknown. We analyzed population genomic data of all five snub-nosed monkey species to assess their genetic diversity, inbreeding level, and genetic load. For R. roxellana, R. bieti, and R. strykeri, population size is positively correlated with genetic diversity and negatively correlated with levels of inbreeding. Other species, however, which possess small population sizes, such as R. brelichi and R. avunculus, show high levels of genetic diversity and low levels of genomic inbreeding. Similarly, in the three populations of R. roxellana, the Shennongjia population, which possesses the lowest population size, displays a higher level of genetic diversity and lower level of genomic inbreeding. These findings suggest that although R. brelichi and R. avunculus and the Shennongjia population might be at risk, it possess significant genetic diversity and could thus help strengthen their long-term survival potential. Intriguingly, R. roxellana with large population size possess high genetic diversity and low level of genetic load, but they show the highest recent inbreeding level compared with the other snub-nosed monkeys. This suggests that, despite its large population size, R. roxellana has likely been experiencing recent inbreeding, which has not yet affected its mutational load and fitness. Analyses of homozygous-derived deleterious mutations identified in all snub-nosed monkey species indicate that these mutations are affecting immune, especially in smaller population sizes, indicating that the long-term consequences of inbreeding may be resulting in an overall reduction of immune capability in the snub-nosed monkeys, which could provide a dramatic effect on their long-term survival prospects. Altogether, our study provides valuable information concerning the genomic impact of population decline of the snub-nosed monkeys. We revealed multiple counterintuitive and unexpected patterns of genetic diversity in small and large population, which will be essential for conservation management of these endangered species.

scholarly journals The Strength of Selection Against Neanderthal Introgression

2015 ◽  
Author(s):  
Ivan Juric ◽  
Simon Aeschbacher ◽  
Graham Coop
Keyword(s):  
Population Size ◽  
Effective Population Size ◽  
Human Population ◽  
Genetic Load ◽  
Purifying Selection ◽  
Small Population ◽  
Secondary Contact ◽  
Human Populations ◽  
Effective Population ◽  
Deleterious Alleles

AbstractHybridization between humans and Neanderthals has resulted in a low level of Neanderthal ancestry scattered across the genomes of many modern-day humans. After hybridization, on average, selection appears to have removed Neanderthal alleles from the human population. Quantifying the strength and causes of this selection against Neanderthal ancestry is key to understanding our relationship to Neanderthals and, more broadly, how populations remain distinct after secondary contact. Here, we develop a novel method for estimating the genome-wide average strength of selection and the density of selected sites using estimates of Neanderthal allele frequency along the genomes of modern-day humans. We confirm that East Asians had somewhat higher initial levels of Neanderthal ancestry than Europeans even after accounting for selection. We find that the bulk of purifying selection against Neanderthal ancestry is best understood as acting on many weakly deleterious alleles. We propose that the majority of these alleles were effectively neutral—and segregating at high frequency—in Neanderthals, but became selected against after entering human populations of much larger effective size. While individually of small effect, these alleles potentially imposed a heavy genetic load on the early-generation human–Neanderthal hybrids. This work suggests that differences in effective population size may play a far more important role in shaping levels of introgression than previously thought.Author SummaryA small percentage of Neanderthal DNA is present in the genomes of many contemporary human populations due to hybridization tens of thousands of years ago. Much of this Neanderthal DNA appears to be deleterious in humans, and natural selection is acting to remove it. One hypothesis is that the underlying alleles were not deleterious in Neanderthals, but rather represent genetic incompatibilities that became deleterious only once they were introduced to the human population. If so, reproductive barriers must have evolved rapidly between Neanderthals and humans after their split. Here, we show that oberved patterns of Neanderthal ancestry in modern humans can be explained simply as a consequence of the difference in effective population size between Neanderthals and humans. Specifically, we find that on average, selection against individual Neanderthal alleles is very weak. This is consistent with the idea that Neanderthals over time accumulated many weakly deleterious alleles that in their small population were effectively neutral. However, after introgressing into larger human populations, those alleles became exposed to purifying selection. Thus, rather than being the result of hybrid incompatibilities, differences between human and Neanderthal effective population sizes appear to have played a key role in shaping our present-day shared ancestry.

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