(2)① Family investigation showed that onychomycosis was passed down from generation to generation. The onychomycosis is dominant, the third father suffers from B disease, and the daughter is normal, which is recessive inheritance of X chromosome. The genotype of III-2 is12aaaxbxbxb or12aaaxbxbxb.
② the genotype of iii-1is AaXBY, and the probability of boys suffering from both A disease and B disease is12×18, and the probability of boys suffering from A disease but not B disease is12× (12+66).
So the answer is:
(1) on the autosome? The number of male and female patients with disease A on X chromosome is basically the same, and the number of male patients with disease B is more than that of female patients.
(2)①aaXBXB or aaXBXB? ② 18? 38