University of Cambridge > Talks.cam > Genetics Seminar  > Evolutionary strata on young mating-type chromosomes despite the lack of sexual antagonism.

Evolutionary strata on young mating-type chromosomes despite the lack of sexual antagonism.

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  • UserProfessor Tatiana Giraud, Departement Genetique et Ecologie Evolutives, Université Paris-Saclay
  • ClockThursday 07 October 2021, 13:30-14:30
  • HouseZoom meeting.

If you have a question about this talk, please contact Caroline Newnham.

Host: John Welch

Sex chromosomes can display successive steps of recombination suppression known as “evolutionary strata”, which are thought to result from the successive linkage of sexually antagonistic genes to sex-determining genes. However, there is little evidence to support this explanation. We show that evolutionary strata have evolved repeatedly without sexual antagonism in fungi : we found in anther-smut fungi suppressed recombination extending beyond loci determining mating compatibility despite lack of male/female roles associated with their mating types. By comparing full-length chromosome assemblies from anther-smut fungi with or without recombination suppression in their mating-type chromosomes, we inferred the ancestral gene order and derived chromosomal arrangements in this group. This approach shed light on the chromosomal fusion underlying the linkage of mating-type loci in fungi and multiple independent cases of chromosomal rearrangements leading to regions of suppressed recombination linking these mating-type loci in closely related species. Such convergent transitions in genomic architecture of mating-type determination indicate strong selection favoring linkage of mating-type loci into cosegregating supergenes. We also found multiple independent evolutionary strata (stepwise recombination suppression) in several species over a range of ages in mating-type chromosomes. Several evolutionary strata did not include genes involved in mating-type determination. The existence of strata devoid of mating-type genes were found in several other fungi and even around other types of supergenes, despite the lack of sexual antagonism, calls for a unified theory of sex-related chromosome evolution. We therefore developed a theoretical model to test alternative hypotheses and showed that recombination suppression can be selected for sheltering deleterious alleles segregating in genomes near a permanently heterozygous allele.

This talk is part of the Genetics Seminar series.

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