Question

A phenotipically normal male married an affected and they *begat* an affected daughter and an affected son. The affected daughter married a normal male and begat two normal sons, an affected daughter and a normal female. Similarly, the affected son married a normal female and begat an affected son and a normal daughter. The affected son (G3) married the normal first cousin and they gave birth to six children, two normal daughters, two affected daughters, an affected son and a normal son.

I. Draw the pedigree chat
II. what's the pattern of inheritance? I.e. is the gene responsible autosomal or sex-linked
III. Is the gene dominant or recessive? Give reasons
IV. if the gene manifesting is C, such that C- is affected, what are the genotypes of I, II, II ~3,   III ~4, III ~5, and IV ~2

Key: ~ = sub-script

Answer 1

I)

II)It is not sex linked as had it been X linked then the affected boy in generation 2 (GII) married a normal girl, their daughter might have been affected but not the son. So it's autosomal.

III) It's a dominant gene. If we see the parents, the mother is affected. So let's say she is CC and the father is normal , so cc. All their progeny will be Cc. Had the disease been autosomal recessive, the affected daughter and son had to be cc. But since they are Cc and still affected, this proves the gene is dominant .

IV) I am giving the genotypes of all of them :

Note : C is the dominant gene .So CC/ Cc = affected .and cc = normal