KCdgw
Posts: 361
Joined: Sep. 2002
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Merlin seems impressed by Sanfords "Y chromosome degeneration" argument:
| Quote | Brian Sykes claims that the y chromosome is deteriorating (might have been a reference to some research on the radio, but I do not remember who or where) which supports Sanford’s position
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I remind him that the evolution of sex chromosomes involves deterioration of the Y:
Dave Wisker:
| Quote | Your comment is awaiting moderation.
Hi merlin,
| Quote | | Brian Sykes claims that the y chromosome is deteriorating (might have been a reference to some research on the radio, but I do not remember who or where) which supports Sanford’s position |
Deterioration of the Y chromosome is expected under evolutionary theory, primarily because of the lack of recombination between X and Y . There is a rich cytogenetic literature on the evolution of sex chromosome systems, going back around 50 years or so. Here’s a recent example:
Engelstädter J (2008). Muller’s Ratchet and the degeneration of Y chromosomes: a simulation study. Genetics 180(2): 957–967.
From the introduction (my emphasis):
MANY animal and plant species have sex determination systems that involve distinct X and Y chromosomes (BULL 1983; SOLARI 1993). It is generally believed that these sex chromosomes evolved from common autosomal ancestors. However, Y chromosomes often have lost many of their genes, are highly heterochromatic, and exhibit a high density of transposable elements (reviewed in GRAVES 2006). In humans, for example, the Y chromosome spans ~60 Mb and contains only a few dozen protein-coding genes in its nonrecombining region (SKALETSKY et al. 2003). Moreover, the Y is rich in repetitive DNA without apparent function, and a large proportion is heterochromatic. By contrast, the human X chromosome measures ~155 Mb and contains >1000 genes (ROSS et al. 2005).
Several mechanisms have been proposed for why Y chromosomes erode, but their relative importance is not fully understood and may vary between species (reviewed in CHARLESWORTH and CHARLESWORTH 2000; BACHTROG 2006). It is clear, however, that the ultimate cause of erosion is the lack of recombination between X and Y chromosomes over most of their length. For example, this lack of recombination can lead to “hitchhiking effects” of deleterious mutations (MAYNARD SMITH and HAIGH 1974): if a beneficial mutation arises on a Y chromosome and spreads to fixation, it will drag along all mildly deleterious mutations at other loci on the Y chromosome (RICE 1987). Another mechanism that leads to accumulation of mildly deleterious alleles is a reduction in effective population size due to “background selection” against linked, strongly deleterious alleles that arise continually by mutation (B. CHARLESWORTH et al. 1993).
http://www.pubmedcentral.nih.gov/article....4#bib43
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Of course, it won't get out of moderation until Tuesday
KC
Edited by KCdgw on May 24 2009,19:42
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