Early-Stage Evolution of the Neo-Y Chromosome in Drosophila albomicans
Date Issued
2011
Date
2011
Author(s)
Chang, Ching-Ho
Abstract
Sex chromosomes evolved independently from autosomes in various lineages. In general, Y chromosome lost most of its genes except for sex determination factors while X chromosome remains gene-rich. The degeneracy of Y-linked genes is caused by accumulation of deleterious mutations as a consequence of recombination inhibition between the sex-chromosome pairs. To decipher the transition from homologous autosomes to differentiated sex chromosomes, the recently fused autosomal regions of the neo-sex chromosomes in Drosophila albomicans provide a good model. Both of its sequence divergence and whole transcriptome profiles were compared to understand the early neo-sex chromosome evolution. I find that most neo-X and neo-Y linked alleles remain under purify selection (dN/dS=0.001/0.021). However, among 1,798 transcripts, 19.0% and 4.0% show significantly reduced gene expression in neo-Y and neo-X linked alleles, respectively. The expression divergence between neo-sex alleles was attributed to both upregulation of neo-X alleles and downregulation of neo-Y. In addition, the genes with expression divergence would have larger sequence divergence between neo-sex alleles. Further analyses reveal that old female-biased genes were prone to reduce the expression of neo-Y alleles, whereas upregulation of neo-Y alleles might shape new male-biased genes. My results indicate that the expression divergence between neo-sex chromosomes is an important step of ealy neo-sex chromosome evolution in D. albomicans.
Subjects
sex chromosome evolution
neo-sex chromosomes
Y chromosome degeneration
sexually antagonistic selection
Drosophila albomicans
transcriptome analysis
Type
thesis
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