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SUMMARY:Evolutionary strata on young mating-type chromosomes despite the l
 ack of sexual antagonism. - Professor Tatiana Giraud\, Departement Genetiq
 ue et Ecologie Evolutives\, Université Paris-Saclay
DTSTART:20211007T123000Z
DTEND:20211007T133000Z
UID:TALK161092@talks.cam.ac.uk
CONTACT:Caroline Newnham
DESCRIPTION:Sex chromosomes can display successive steps of recombination 
 suppression known as “evolutionary strata”\, which are thought to resu
 lt from the successive linkage of sexually antagonistic genes to sex-deter
 mining genes. However\, there is little evidence to support this explanati
 on. We show that evolutionary strata have evolved repeatedly without sexua
 l antagonism in fungi : we found in anther-smut fungi suppressed recombina
 tion extending beyond loci determining mating compatibility despite lack o
 f male/female roles associated with their mating types. By comparing full-
 length chromosome assemblies from anther-smut fungi with or without recomb
 ination suppression in their mating-type chromosomes\, we inferred the anc
 estral gene order and derived chromosomal arrangements in this group. This
  approach shed light on the chromosomal fusion underlying the linkage of m
 ating-type loci in fungi and multiple independent cases of chromosomal rea
 rrangements leading to regions of suppressed recombination linking these m
 ating-type loci in closely related species. Such convergent transitions in
  genomic architecture of mating-type determination indicate strong selecti
 on favoring linkage of mating-type loci into cosegregating supergenes. We 
 also found multiple independent evolutionary strata (stepwise recombinatio
 n suppression) in several species over a range of ages in mating-type chro
 mosomes. Several evolutionary strata did not include genes involved in mat
 ing-type determination. The existence of strata devoid of mating-type gene
 s were found in several other fungi and even around other types of superge
 nes\, despite the lack of sexual antagonism\, calls for a unified theory o
 f sex-related chromosome evolution. We therefore developed a theoretical m
 odel to test alternative hypotheses and showed that recombination suppress
 ion can be selected for sheltering deleterious alleles segregating in geno
 mes near a permanently heterozygous allele.\n\n
LOCATION:Zoom meeting
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