From: Josh Bembenek (jbembe@hotmail.com)
Date: Tue Apr 29 2003 - 12:09:27 EDT
Dr. Campbell-
"Secondly, chromosome number can change through duplication or deletion of
chromosomes. Finally, polyploidy or aneupoidy resulting from atypical
fertilization or errors in mitosis or meiosis can result in changes in
chromosome number. Downs syndrome is an example of having an extra
chromosome in humans. Wheat is a successful example of extra chromosomes
through polyploidy. It has three sets of chromosomes and evidently
originated through two hybridization events."
-Great post, very clear. You highlighted the issue I have: normally when
you think of aneuploidy and errors in chromosome numbers you think cancer or
downs. I am familiar with plants and other organisms having more
malleability in their genome, but generally mammals have much more problems
with a lack of fidelity in chromosome inheritance/ ploidy.
"Advanced and primitive are somewhat problematic terms, but high chromosome
numbers occur here and there among many types of organisms. For example,
some tiny clams have close to two hundred chromosomes. As parthenogenetic
polyploid hybrids, they do not have to sort the chromosomes for meiosis."
-I work in the cell cycle area, so this interests me. Can you explain your
terminology here, I am not familiar with parthenogenetic polyploid, and how
that relates to chromosome segregation in meiosis.
"The puzzle for groups in which chromosome number is highly variable is why,
not how. Changing chromosome number is not that hard, though it may be
difficult to reproduce successfully if self-fertilization or asexuar
reproduction are not options. Why certain taxa vary widely whereas others
show hardly any differences is not known to me."
-This is the exact difficulty I was thinking of. Naturally advantageous
changes in chromosomes among mammals is difficult to imagine, especially in
terms of reproduction.
Josh
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