(1) As can be seen from the table data, there are 279+6=285 males and 28 1+2=283 females suffering from onychomycosis, and the number of males and females is basically the same. The incidence of onychomycosis has nothing to do with sex, and onychomycosis is most likely located on the autosome. Male patients with B are 250+6=256, and female patients 16+2= 18. There are obviously more male patients than female patients. According to the characteristics of sex-linked inheritance, the pathogenic gene of B is most likely located on the X chromosome.

(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