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United States Department of Agriculture

Agricultural Research Service

Title: The Papaya Y Chromosome Evolved Recently and Shows Gene Paucity and DNA Sequence Expansion)

Author
item Yu, Qingyi
item Hou, Shaobin
item Feltus, Alex
item Moore, Richard
item Moore, Paul
item Alam, Masqsudul
item Jiang, Jiming
item Paterson, Andrew
item Ming, Ray

Submitted to: Plant and Animal Genome Conference
Publication Type: Abstract only
Publication Acceptance Date: 10/2/2006
Publication Date: N/A
Citation:

Interpretive Summary: Not applicable

Technical Abstract: Sex chromosomes in flowering plants, in contrast to those in animals, evolved relatively recently and only a few are heteromorphic. At cytological level, the sex chromosomes of papaya appear homomorphic, nevertheless, we are finding the papaya Y chromosome shows features of incipient sex chromosome evolution. To survey the state of Y chromosome differentiation, we sequenced two pairs of X and Y specific bacterial artificial chromosomes (BACs) and conducted functional analysis on two X BACs and seven Y BACs. Sequence comparison between the two paired X and Y BACs revealed three inversion events on the MSY. Aligning the paired BAC sequences showed that one of the Y BACs had expanded by 9.6% and the other Y BAC had expanded by 30%. One gene on the Y chromosome had been lost by deletion, while the corresponding gene on the X chromosome is still functioning. The average gene density was 1 gene per 35kb on 420 kb X BACs, but only 1 gene per 171 kb on 1.2 Mb Y BACs, a five fold reduction on the Y chromosome. Analysis of sequence divergence between X and Y gene pairs indicates that the majority of X-Y gene pairs investigated are functionally constrained, a characteristic of young sex chromosomes. Our estimate of the age of divergence between X-Y gene pairs ranges from 1.3-2.8 million years ago, supporting a recent origin of the primitive sex chromosomes in papaya. Our findings demonstrate the features and consequence of sex chromosome evolution in this primitive X and Y system of papaya.

Last Modified: 8/24/2016
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