Evolution of neo-sex chromosomes in Drosophila albomicans
Date Issued
2008
Date
2008
Author(s)
Chang, Te-Pin
Abstract
Drosophila albomicans has a pair of neo-sex chromosomes which composed 60% of the genome (i.e., fused 3-X and 3-Y) and the homologous 3rd chromosome is still an autosome of its sibling species D. nasuta. Generally speaking, the Y chromosome contains only a small number of genes and its major components are heterochromatin. Because of the fusion events between the autosome and sex chromosomes, D. albomicans became a promising material to study the early stage of sex chromosomes. Homologous sequences on the 3rd chromosome can be used to study sex chromosome differentiation after the cessation of recombination, such as the accumulation of sexual antagonistic alleles favoring males, Y chromosome degeneration and the neo-sex chromosome divergence time of D. albomicans. The SSH cDNA library of males did not show a significant higher proportion of male specifically expressed genes located on this neo-sex chromosome arms, but their evolution rate is higher as expected. Also as expected, genes on the sex chromosome were shown to be under higher selection pressure, and found the evolution rate is higher of the male-specific expression genes than other ones. The divergence time of the neo-sex chromosomes is about 70,000 years according to the 25 alleles of X and Y homologous sequences. There’s no significant degeneration found on the neo-Y chromosome, however, an allele of the gene Amyrel on the Y chromosome with a 206 bp deletion and a premature stop codon was found polymorphically existed in the Yunnan population. It shows there’s no obvious degeneration of Y chromosome at this early stage; nevertheless, a degenerate allele polymorphically existed.
Subjects
cDNA library
degeneration
Drosophila albomicans
D. nasuta
male-specific expressed gene
sex chromosome
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-97-F88632003-1.pdf
Size
23.53 KB
Format
Adobe PDF
Checksum
(MD5):f3f62700f3b3a173613fcc57dd44c358