Abstract:
:Chromosome size and morphology vary within and among species, but little is known about the proximate or ultimate causes of these differences. Cichlid fish species in the tribe Oreochromini share an unusual giant chromosome that is ∼3 times longer than the other chromosomes. This giant chromosome functions as a sex chromosome in some of these species. We test two hypotheses of how this giant sex chromosome may have evolved. The first hypothesis proposes that it evolved by accumulating repetitive elements as recombination was reduced around a dominant sex determination locus, as suggested by canonical models of sex chromosome evolution. An alternative hypothesis is that the giant sex chromosome originated via the fusion of an autosome with a highly repetitive B chromosome, one of which carried a sex determination locus. We test these hypotheses using comparative analysis of chromosome-scale cichlid and teleost genomes. We find that the giant sex chromosome consists of three distinct regions based on patterns of recombination, gene and transposable element content, and synteny to the ancestral autosome. The WZ sex determination locus encompasses the last ∼105Mbp of the 134Mbp giant chromosome. The last 47Mbp of the giant chromosome shares no obvious homology to any ancestral chromosome. Comparisons across 69 teleost genomes reveal that the giant sex chromosome contains unparalleled amounts of endogenous retroviral elements, immunoglobulin genes, and long non-coding RNAs. The results favor the B chromosome fusion hypothesis for the origin of the giant chromosome.
journal_name
Mol Biol Evoljournal_title
Molecular biology and evolutionauthors
Conte MA,Clark FE,Roberts RB,Xu L,Tao W,Zhou Q,Wang D,Kocher TDdoi
10.1093/molbev/msaa319subject
Has Abstractpub_date
2020-12-10 00:00:00eissn
0737-4038issn
1537-1719pii
6029583pub_type
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