Liu Zhiyong, Moore Paul H, Ma Hao, Ackerman Christine M, Ragiba Makandar, Yu Qingyi, Pearl Heather M, Kim Minna S, Charlton Joseph W, Stiles John I, Zee Francis T, Paterson Andrew H, Ming Ray
Hawaii Agriculture Research Center, Aiea, Hawaii 96701, USA.
Nature. 2004 Jan 22;427(6972):348-52. doi: 10.1038/nature02228.
Many diverse systems for sex determination have evolved in plants and animals. One involves physically distinct (heteromorphic) sex chromosomes (X and Y, or Z and W) that are homozygous in one sex (usually female) and heterozygous in the other (usually male). Sex chromosome evolution is thought to involve suppression of recombination around the sex determination genes, rendering permanently heterozygous a chromosomal region that may then accumulate deleterious recessive mutations by Muller's ratchet, and fix deleterious mutations by hitchhiking as nearby favourable mutations are selected on the Y chromosome. Over time, these processes may cause the Y chromosome to degenerate and to diverge from the X chromosome over much of its length; for example, only 5% of the human Y chromosome still shows X-Y recombination. Here we show that papaya contains a primitive Y chromosome, with a male-specific region that accounts for only about 10% of the chromosome but has undergone severe recombination suppression and DNA sequence degeneration. This finding provides direct evidence for the origin of sex chromosomes from autosomes.
植物和动物中已经进化出了许多不同的性别决定系统。其中一种涉及形态上不同（异型）的性染色体（X和Y，或Z和W），在一种性别（通常为雌性）中是纯合的，而在另一种性别（通常为雄性）中是杂合的。性染色体进化被认为涉及性别决定基因周围重组的抑制，使一个染色体区域永久杂合，该区域随后可能通过穆勒棘轮积累有害的隐性突变，并在Y染色体上选择附近的有利突变时通过搭便车固定有害突变。随着时间的推移，这些过程可能导致Y染色体退化，并在其大部分长度上与X染色体分化；例如，人类Y染色体只有5%仍然显示X-Y重组。我们在此表明，木瓜含有一条原始的Y染色体，其雄性特异性区域仅占该染色体的约10%，但已经经历了严重的重组抑制和DNA序列退化。这一发现为性染色体源于常染色体提供了直接证据。
