|MadSci Network: Genetics|
Dear A., People with only 1 sex chromosome have abnormalities - Turner's syndrome women have all sorts of problems. I think they are also infertile. You have to think of this from a different perspective. Now, if you only had 1 sex chromosome then 1) Mating would be unnecessary. We'd all just have to give birth to clones so males would be unnecessary. There'd be no variation in the population. 2) Variation in offspring means that some with have advantages over the others in the face of environmental changes. 3) The 2 chromosomes are there so that a process called RECOMBINATION can take place during the formation of eggs or sperm. Parts of the two chromosomes are swapped around so that all the eggs or sperm are different, leading to greater variability in the offspring - this facilitates no 2. In women the x chromosomes are randomly inactovated in cells so although only 1 is expressed in any given cell, both are being expressed throughout the body. Hope this helps, Yvonne key words to look up Recombination - meiotic Genetic Variation Turner's syndrome Kleinfelter's Barr bodies Admin note: Some of the bad consequences in Turner syndrome might be due to the fact that not all genes on the "inactive" X are actually inactivated. In fact, there are about 35 genes that still remain active. Females might need two copies of the active genes in order to develop into "proper" women, while males might only need one copy to be male. Look up "X-inactivation" and "escapers" on Pubmed or on the WWW.
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