Question

ignore my markings. If its a X-linked recessive mutation, i presume the mutated X is coming from the father. So then, why is the Parental Generation male unaffected???

points) Consider the below pedigree for hemophilia, caused by a completely penetrant, X-1 .cessive mutation. tx ta Xaxt xt Xtxt xt ya x X xtya x Y xty > +9 (a) What is the probability that II:2 is a carrier?

Answer 1

Even if the male parent is unaffected, the son can be affected if it is a sex linked recessive trait. First you need to know the genotypes for this trait -

Normal male = XY

Affected male = XaY

Normal female = XX, XaX (carrier female)

Affected female = XaXa

Carrier female is phenotypically normal but carries the affected allele. So, she will pass on this trait to 50% of her sons because a son always gets the X chromosome from the mother (thats why is a father is normal, son can be affected). And 50% of the daughters will be carriers, if this carrier female mates with a normal male (XY).

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