On the one hand, the emergence of asynaptic meiosis and the associated loss of the meiotic function of the PAR may have resulted in relaxed selection on the X and Y and, consequently, the rapid accumulation of sex chromosome heterochromatin.
If, instead, repeats arise from spontaneous DNA repair events, they may be distributed among a larger number of historical repair sites and are unlikely to be conserved between species. Population divergence, measured as F STwas calculated using— weir-fst-pop.
Jewish Virtual Library - Duisburg, Germany. Sinauer Associates, Inc. They are specialized for motility, seeking out an egg cell and fusing with it in a process called fertilization. The handicap principle: a missing piece of Darwin's puzzle.
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No genes are shared between the avian ZW and mammal XY chromosomes,  and from a comparison between chicken and human, the Z chromosome appeared similar to the autosomal chromosome 9 in human, rather than X or Y, suggesting that the ZW and XY sex-determination systems do not share an origin, but that the sex chromosomes are derived from autosomal chromosomes of the common ancestor of birds and mammals.
Individual organisms which produce both male and female gametes are termed hermaphroditic. Annual Review of Genetics. Regina Bailey. Gametes are also called sex cells. A mutation occurring in one of these genes could lead to the development of an altered trait.
Johnston, I. Toder R. We find that Open in a separate window. Nor was it detected during selection sweep analysis in a study that explicitly explored the potential consequences imposed by the whole genome duplication The approach allowed a direct comparison of nucleotide diversity between populations Fig.