THE EVOLUTION OF XY RECOMBINATION: SEXUALLY ANTAGONISTIC SELECTION VERSUS DELETERIOUS MUTATION LOAD

AbstractDeleterious mutations accumulating on non-recombining Y chromosomes can drive XY to XY turnovers, but are thought to prevent XY to ZW turnovers, because the latter require fixation of the ancestral Y. Using individual-based simulations, we explored whether and how a dominant W allele can spread in a young XY system that gradually accumulates deleterious mutations. We also investigated how sexually antagonistic (SA) polymorphism on the ancestral sex chromosomes, and the mechanism controlling X-Y recombination suppression affect these transitions. In contrast with XY to XY turnovers, XY to ZW turnovers cannot be favored by Y chromosome mutation load. If the arrest of X-Y recombination depends on genotypic sex, transitions are strongly hindered by deleterious mutations, and totally suppressed by very small SA cost, because deleterious mutations and female-detrimental SA alleles would have to fix with the Y. If, however, the arrest of X-Y recombination depends on phenotypic sex, X and Y recombine in XY ZW females, allowing for the purge of Y-linked deleterious mutations and loss of the SA polymorphism, causing XY to ZW turnovers to occur at a neutral rate. We generalize our results to other types of turnovers (e.g., triggered by non-dominant sex-determining mutations) and discuss their empirical relevance.

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Evolution of haploid selection in predominantly diploid organisms

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1512004112 ◽

2015 ◽

Vol 112 (52) ◽

pp. 15952-15957 ◽

Cited By ~ 29

Author(s):

Sarah P. Otto ◽

Michael F. Scott ◽

Simone Immler

Keyword(s):

Deleterious Mutation ◽

Empirical Studies ◽

Deleterious Mutations ◽

Mutation Load ◽

Maternal Control ◽

Antagonistic Selection ◽

Male Gametes ◽

Diploid Complement ◽

Haploid Selection ◽

Average Fitness

Diploid organisms manipulate the extent to which their haploid gametes experience selection. Animals typically produce sperm with a diploid complement of most proteins and RNA, limiting selection on the haploid genotype. Plants, however, exhibit extensive expression in pollen, with actively transcribed haploid genomes. Here we analyze models that track the evolution of genes that modify the strength of haploid selection to predict when evolution intensifies and when it dampens the “selective arena” within which male gametes compete for fertilization. Considering deleterious mutations, evolution leads diploid mothers to strengthen selection among haploid sperm/pollen, because this reduces the mutation load inherited by their diploid offspring. If, however, selection acts in opposite directions in haploids and diploids (“ploidally antagonistic selection”), mothers evolve to reduce haploid selection to avoid selectively amplifying alleles harmful to their offspring. Consequently, with maternal control, selection in the haploid phase either is maximized or reaches an intermediate state, depending on the deleterious mutation rate relative to the extent of ploidally antagonistic selection. By contrast, evolution generally leads diploid fathers to mask mutations in their gametes to the maximum extent possible, whenever masking (e.g., through transcript sharing) increases the average fitness of a father’s gametes. We discuss the implications of this maternal–paternal conflict over the extent of haploid selection and describe empirical studies needed to refine our understanding of haploid selection among seemingly diploid organisms.

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Harmful mutation load in the mitochondrial genomes of cattle breeds

BMC Research Notes ◽

10.1186/s13104-021-05664-y ◽

2021 ◽

Vol 14 (1) ◽

Author(s):

Sankar Subramanian

Keyword(s):

Population Size ◽

Artificial Selection ◽

Deleterious Mutation ◽

Genetic Diseases ◽

Mitochondrial Genomes ◽

Deleterious Mutations ◽

Founder Population ◽

Mutation Load ◽

Effective Population ◽

Cattle Breeds

Abstract Objective Domestication of wild animals results in a reduction in the effective population size, and this could affect the deleterious mutation load of domesticated breeds. Furthermore, artificial selection will also contribute to the accumulation of deleterious mutations due to the increased rate of inbreeding among these animals. The process of domestication, founder population size, and artificial selection differ between cattle breeds, which could lead to a variation in their deleterious mutation loads. We investigated this using mitochondrial genome data from 364 animals belonging to 18 cattle breeds of the world. Results Our analysis revealed more than a fivefold difference in the deleterious mutation load among cattle breeds. We also observed a negative correlation between the breed age and the proportion of deleterious amino acid-changing polymorphisms. This suggests a proportionally higher deleterious SNPs in young breeds compared to older breeds. Our results highlight the magnitude of difference in the deleterious mutations present in the mitochondrial genomes of various breeds. The results of this study could be useful in predicting the rate of incidence of genetic diseases in different breeds.

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Nature of Deleterious Mutation Load in Drosophila

Genetics ◽

10.1093/genetics/144.4.1993 ◽

1996 ◽

Vol 144 (4) ◽

pp. 1993-1999 ◽

Cited By ~ 5

Author(s):

Peter D Keightley

Keyword(s):

Deleterious Mutation ◽

Spontaneous Mutation ◽

Mutation Accumulation ◽

Mutation Rates ◽

Mutation Load ◽

Spontaneous Mutation Rate ◽

A Minor ◽

Chromosome I ◽

Balancer Chromosomes ◽

Balancer Chromosome

Much population genetics and evolution theory depends on knowledge of genomic mutation rates and distributions of mutation effects for fitness, but most information comes from a few mutation accumulation experiments in Drosophila in which replicated chromosomes are sheltered from natural selection by a balancer chromosome. I show here that data from these experiments imply the existence of a large class of minor viability mutations with approximately equivalent effects. However, analysis of the distribution of viabilities of chromosomes exposed to EMS mutagenesis reveals a qualitatively different distribution of effects lacking such a minor effects class. A possible explanation for this difference is that transposable element insertions, a common class of spontaneous mutation event in Drosophila, frequently generate minor viability effects. This explanation would imply that current estimates of deleterious mutation rates are not generally applicable in evolutionary models, as transposition rates vary widely. Alternatively, much of the apparent decline in viability under spontaneous mutation accumulation could have been nonmutational, perhaps due to selective improvement of balancer chromosomes. This explanation accords well with the data and implies a spontaneous mutation rate for viability two orders of magnitude lower than previously assumed, with most mutation load attributable to major effects.

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The mutation load under tetrasomic inheritance and its consequences for the evolution of the selfing rate in autotetraploid species

Genetics Research ◽

10.1017/s0016672399003845 ◽

1999 ◽

Vol 74 (1) ◽

pp. 31-42 ◽

Cited By ~ 59

Author(s):

J. RONFORT

Keyword(s):

Inbreeding Depression ◽

Deleterious Mutation ◽

Stable State ◽

Approximate Solutions ◽

Balance Model ◽

Deleterious Mutations ◽

Selfing Rate ◽

Mutation Load ◽

Mean Fitness ◽

The Mean

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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