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allison11111

Sex influenced vs sex linked

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is sex linked and sex influenced the same thing? do traits that fall under either category also apply to the other one?

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A sex linked trait is determined by gene loci on the X or Y chromosomes, whereas a sex influenced trait is one whose basic loci are not on the sex chromosomes but whose   penetrance or expressivity is influenced by factors such as estrogenic or androgenic hormone levels. An example of a sex linked trait is color-blindness, while traits like coarseness of body hair, bone density or muscle strength is closely associated with absolute or relative levels of estrogen & androgens....It's been said that embryologically (& figuratively) speaking, we all start out as females, but those that start making enough testosterone at the right time become males.

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allison, if that doesn't seem clear.

The X and Y chromosomes kick off hormosomal changes such as puberty. The hormones involved can then influence genes that are not themselves located on the X or Y chromosomes. Hence "sex influenced".

"Sex Linked" means that the gene is physically on the X or Y chromosomes. Inheritance can be quite distinct  with sex linked genes, as the Y chromosome is MUCH smaller than the X chromosome and is missing many genes that are on the X chromosome. (While there are Y linked allelles, the X linked can be more obvious). Many X linked genes have no corresponding gene on the Y chromosome. So inheritance is entirely determined by the X chromosome for sons with those X linked genotypes.

 

Hope that helps.

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