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Oolon Colluphid · 01-20-2003, 05:18 AM

Quote:

Originally posted by Doubting Didymus

This would require animals, plants, and also fungi to have all derived sex from the same source. I'm no expert, but that sounds a bit iffy to me. Fungus sex is so different to animal and plant sex, that I find it hard to picture them all deriving from the same ancestor.

I'll check for details, but last time I read anything about this, I heard that fungi and animals are actually more closely related than either is to plants. Fungi looking like plants misleads us intuitively, but it makes sense since they're both heterotrophs, lacking the chloroplast-symbiosis thingy.

Will research tonight and see if Brock, Raven and the rest can make sense of what my lousy memory throws up

DT

[Edited: note to self: read all the other posts before replying. D'oh! Sorry DD, should have known you knew that. But have left the post intact since for some odd reason I quite like the idea of being nearer to a mushroom than a cabbage

]

KC · 01-20-2003, 05:59 AM

One of the more interesting aspects of this is the evolution of sex chromosomes. Different groups maintain sex differences through sex chromosomes in varied ways. Some have numerous sex chromosomes-- there are beetle species with as many as 27 or more--while some, like honeybees, use the entire gemome: males are haploid, females are diploid. There are fish whose sexes differ by only one gene.

What they seem to have in common evolutionarily is that the sex chromosomes start out as homologous autosomes (matched non-sex chromosomes), and in some manner one of them acquires and maintains enough differences to prevent recombination with its partner in the area determining one sex. This has some interesting consequences, most notable being that the areas which cannot recombine tend to be vulnerable to mutation, and become less and less functional over time, leading to shrinkage and decay. This, of course, is not a stable arrangement. As long as the two chromsomes can pair at meiosis, then proper segregation can occur, but if decay proceeds to the point where pairing is difficult or impossible, things get unpredictable. I read some time ago that in some groups (insects, as I recall) there is evidence of an original sex chromosome degenerating to the point where the ability to pair was lost, and another chromosome pair taking over the role of determining sex differences. Unfortunately, I don't have the references handy for that, and my memory is hazy.

There is an interesting article on the evolution of human sex chromosomes in the February 2001 issue of Scientific American.

Cheers,

KC

GodLessWarrior · 01-20-2003, 06:59 AM

These are outstanding links from PBS's evolution series part 5: Why Sex?

http://www.pbs.org/wgbh/evolution/sex/index.html

http://www.pbs.org/wgbh/evolution/li.../l_015_01.html

And this is just great for evolution anyway:
http://www.pbs.org/wgbh/evolution/library/index.html

Itzpapalotl · 01-20-2003, 04:20 PM

at least one mammal has lost its Y chromsome.

In the mole vole Ellobius lutescens both males and females are XX and the normal mammalian sex determining gene SRY is no longer present. The genetics of sex determination in this animal still remain obscure as so far all the candidate genes proposed as possible male determining factors have been rejected.

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01-20-2003, 05:59 AM	#12
KC Senior Member Join Date: Mar 2002 Location: San Narcisco, RRR Posts: 527	One of the more interesting aspects of this is the evolution of sex chromosomes. Different groups maintain sex differences through sex chromosomes in varied ways. Some have numerous sex chromosomes-- there are beetle species with as many as 27 or more--while some, like honeybees, use the entire gemome: males are haploid, females are diploid. There are fish whose sexes differ by only one gene. What they seem to have in common evolutionarily is that the sex chromosomes start out as homologous autosomes (matched non-sex chromosomes), and in some manner one of them acquires and maintains enough differences to prevent recombination with its partner in the area determining one sex. This has some interesting consequences, most notable being that the areas which cannot recombine tend to be vulnerable to mutation, and become less and less functional over time, leading to shrinkage and decay. This, of course, is not a stable arrangement. As long as the two chromsomes can pair at meiosis, then proper segregation can occur, but if decay proceeds to the point where pairing is difficult or impossible, things get unpredictable. I read some time ago that in some groups (insects, as I recall) there is evidence of an original sex chromosome degenerating to the point where the ability to pair was lost, and another chromosome pair taking over the role of determining sex differences. Unfortunately, I don't have the references handy for that, and my memory is hazy. There is an interesting article on the evolution of human sex chromosomes in the February 2001 issue of Scientific American. Cheers, KC

01-20-2003, 06:59 AM	#13
GodLessWarrior Junior Member Join Date: Dec 2002 Location: Boston, MA Posts: 64	These are outstanding links from PBS's evolution series part 5: Why Sex? http://www.pbs.org/wgbh/evolution/sex/index.html http://www.pbs.org/wgbh/evolution/li.../l_015_01.html And this is just great for evolution anyway: http://www.pbs.org/wgbh/evolution/library/index.html

01-20-2003, 04:20 PM	#14
Itzpapalotl Junior Member Join Date: Oct 2002 Location: UK Posts: 12	at least one mammal has lost its Y chromsome. In the mole vole Ellobius lutescens both males and females are XX and the normal mammalian sex determining gene SRY is no longer present. The genetics of sex determination in this animal still remain obscure as so far all the candidate genes proposed as possible male determining factors have been rejected.

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