linked and sex linked genes? how to determine?

[sangria1986]

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What are some frequent things to look out for when trying to tell if a genetic disorder or perhaps data provided indicate that genes are linked or sex linked? also how to tell if recombination is taking place?

 

[methylethyl88]

two different genes are linked if they are on the same chromosome and are located close to each other on that chromosome. If two genes are on the same chromosomes but are far apart from each other on that chromosome, the chances for recombination are much more likely.

An simply way to tell if a gene is sex-linked when looking at a pedigree chart for example is seeing if the incidence of the disease is equal among males and females.

 

[Rabolisk]

All sex linked genes are X-linked and mostly recessive. X-linked dominant is rare. The following is for X-linked recessive.

Males can only be affected or not affected. No such thing as male carriers.
Males receive genes only from the mother.
All affected males have carrier or affected mother.
All males whose mother is affected will also be affected.
Males do not pass genes onto their sons.
All females with affected father are carriers.
All females with affected mother are carriers.
In general, males are affected much more than females.

Often times, generation 1 male will be affected, generation 2 female will be a carrier, and generation 3 male will also be affected.

 

[549]

If a trait is sex-linked (located on the X/Y chromosome) then the proportion of affected females and males will be different. So for example, if you are given a pedigree and asked whether the trait is autosomal or sex-linked, count the proportion of affected:total females and the proportion of affected:total males and if they are very different, it is sex-linked, but if they are similar, it is autosomal. If it is Y-linked the trait will be seen in every male, but if it is X-linked it will be in some males and some females.

Recombination produces new combinations of alleles not found in the parents, so look for that to determine whether recombination has occurred.

 

[ElliottB]

All sex linked genes are X-linked and mostly recessive. X-linked dominant is rare. The following is for X-linked recessive.

Males can only be affected or not affected. No such thing as male carriers.
Males receive genes only from the mother.
All affected males have carrier or affected mother.
All males whose mother is affected will also be affected.
Males do not pass genes onto their sons.
All females with affected father are carriers.
All females with affected mother are carriers.
In general, males are affected much more than females.

Often times, generation 1 male will be affected, generation 2 female will be a carrier, and generation 3 male will also be affected.

This is a good guide to use. Think of male-pattern baldness as an example of sex linked recessive... My maternal grandfather had wicked receding hairline, passed that gene to my unaffected mother, and she gave it to me. Now my hairline is creeping up to the top of my head.