genetic 15 - basicq

[ArchivalUser]

phenotypically normal second cousins marry and wud like to have a child.they are aware that one ancestor{great grandfather}had PKU and r concerned about having an affected offspring.wht is the probability that the child will be affected?

1-1/64
2-1/128
3-1/32
4-1/166

[ArchivalUser]

---is is this about the fact that second cousins share 1/32 of genes....which is called coeffecient of relationship...and hence 1/32 chance of getting the recessive disease when the child is compared to the general population.....

[ArchivalUser]

1111111

the chance of their grand parents for carrier is 100% =1
the chance for their parents to be carriers= 1/2 , 1/2
the chance for them both to be carriers = 1/2, 1/2
the chance they produce an affected offspring =1/4
so 1/2*1/2*1/2*1/2*1/4= 1/64

[ArchivalUser]

remember guys siblings share 1/2 of their genes
1st cousin shre 1/8 of their genes
2nd cousin share 1/32 of their genes

as disease is AR chance of producing affected child will be 1/4 *1/32= 1/64
as ferrari also explained..