Sex linkage question with diagrams.. (1 Viewer)

[SophJI]

sorry to bother...i just drew up the question

I just drew that family

and it is believed the mother is definetiely a carrier of a diease

and dad is not sure


the question was

" is this sex linkage?" explain by referring to the diagram


can anyone helo? i am so stuck

plz look at the attachment

i am so sure the monther is X^A X^a
this means she is a carrier

and dad is X^A and Y



is this a sex linkage??

sorry to confuse

 

[Timothy.Siu]

the mother is X^affected X^normal
father is X^normalY

if u draw a punnet square, (u dont have to), u can find out that it cant be sex linked inheritance because with this combo u cant have a female affected.

i hope u understand

 

[jet]

In a question like this your first instinct should be no because a female is affected. There is a very low probability of this happening if the disease is sex linked.

 

[samthebear]

no i dont think this is sex linked - i think it may be more of the case of dominant/recessive. both parents being carriers of a disease (the disease is recessive - thus not being expressed in the hetrozygous genotype) and the disease is expressed in their children having the homozygous recessive gene.

And if you do the punnet square as Timothy.Siu suggested it shows that no female can express the gene. The reason being that while females inherit one X-chromosome from either parent, the dominant X-chromosome (which is not affected by the disease) inherited from the father over-shadows any recessive X-chromosome (which carries the disease) inherited from the mother. In this way, females can be carriers but cannot express the disease (as seen in the diagram, a female is affected so in this instance cannot be a sex linked trait.)

(not very relevant but still relevant to sex-linked traits using the same example of a mother who is a carrier but a father who is normal) Males on the other hand will have a 50-50 chance of being affected by the diease because they can either inherit one dominant X-chromosome (not carrying the disease) from their mother or one recessive X-chromosome (which carries the disease).

 

[SophJI]

Thank you to those replied..i think i get it!!