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Heredity and sex linked characteristics-possible male carrier?

by TheSkyKing
Tags: carrier, heredity, linked, male
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TheSkyKing
#1
Dec3-04, 01:05 PM
P: 24
A discussion came to surface in my Biology II AP class about heredity and sex linked characteristics. Now with a female carrying two X gametes and a male containing an X and Y gamete, males are more prone to inherit sex linked characteristics such as red-green color blindness and hemophilia. The reason so being because in order for a female to inherit the disease she would have to have the traits on both of her X gametes, meaning that her mom would have to be a carrier or have it while her dad had it. Otherwise, if she has just one X chromosome with the trait she is only a carrier. The reason a male is so prone to inheritence of these traits is because he only needs his X chromosome to contain the trait in order for it to be expressed. My question is, is it possible for a male to be a carrier while having the gene unexpressed? You never know with science...most times there are exceptions. So if anyone knows the answer please reply. Thank you.
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iansmith
#2
Dec3-04, 02:59 PM
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Here a minor rephrasing for your explanation (It might be nippicking). The male is affect by the mutation because it only carries one copy of X (i.e. 1 gene copy) whereas female carry two X chromosome (i.e. 2 gene copy). If the non-mutated gene is dominant, there will be no problem in female carrying the mutated gene. If the mutated gene is dominant, then there is a problem for a female carrier. For the male, the only copy carried is the dominant gene, so the disease is present. In male, one copy of the gene is usually sufficient for functionnality.

As far as I know, there is no example for what you describe but we can speculate.

The question to ask is "What is responsible for the under-expression of the gene". Gene expression is control by specific promoters and/or inhibitors that bind to regulatory region upstream of the gene. If the promoter region of the unexpressed gene is deficient, then it is necessarily sex-linked. This more likely to cause a condition only related to one gene.

First, there might be a defect with the promoter. If the promoter does not work, the gene will no be expressed. Assume that the promoter is on the X or Y chromosome, then there will be no difference between male and female because it is not sex link. If the promotor is sex link, then male represent a large percentage of the affected population. If the promotor or affected, then the disease condition will be related to several genes.

You can also go to more complex example such as the promoter of inhibiter is not functional or the promotor region of an inhibiter is not functional. It will always depend on the location of the mutation. If it is on the X then it is sex-linked.


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