HELP- sex linkage!! (1 Viewer)

[ugly14]

ok, im struggling to understand this and i would really appreciate any clarifications on this topic.

how can you tell if a disease is sex linked or not by looking at the pedigree??? say they give you a pedigree and ask you if the disease is sex linked or not, how do you work it out? im confused!

 

[ugly14]

thanx "sunlightstarz" for that...i do understand what you're talking about. but if you've seen the 2002 HSC bio paper in the multiple choice there's a question like that and i dont know if its sex linked or not, there's no pattern and its dominant. its really bothering me..i cant work it out

when you say "In many cases, a person with a sex-linked trait has parents that don't demonstrate the trait. " how do we know if its linked or not, do i use the X and Y etc... but that still wouldnt tell us if its sex linked or not, it just shows whether a person is a carrier or "diseased"

help!

 

[Survivor39]

If it is an X-linked recessive disease, you should see that in all cases, an affected FEMALE will pass on the disease to ALL of her MALE offspring. This is what you look for. In order for female to get the disease, the father MUST be affected, with/without the mother being affected.

In normal dominant/recessive non-sex-linked cases, you should see about equal sex being affected. Recessive -> look for affected offspring with unaffected parents.

When you do this sort of questions, you need to consider all the possibilities. Can this pedigree show a dominant inheretance? Recessive? Then you go on to look for possible X-linkage. Y-linkage is rare.

I hope this helps.

 

[ugly14]

thank you for saving my life!!! i luv u guys :uhhuh:

 

[Helplessness]

lol. funny title. seems like it belongs in the love and relationships forum. i don't understand 2002 paper MC Q11 either. dominant gene?? Why??

 

[kacca29]

The trait is dominant because it is not recessive!

Look at the two affected parents in generation II, who have one affected child and two unaffected ..... if the trait was recessive, parents would be kk and kk genotypes, so all children would be kk and thus affected. Therefore the trait is dominant. This holds whether the trait is sex-linked or not (try it).

Once you know it's dominant, then it can't be sex-linked because the grandfather (generation I male) carries the trait, if it was sex-linked he would pass the trait on to all his female offspring, because they all recieve the X chromosome from him.

If you can't see this, try drawing the punnett squares for the different possibilities. It gets much easier with practice.