Question

Hemophilia is a genetic blood disorder where normal clotting of the blood at the site of a wound or injury does not occur. Tom (III-1) has hemophilia, but neither of his parents have it. However, his mother’s father (I-1) (Tom's maternal grandfather) does have it. In fact, no females have ever displayed the trait in Tom's family, but several males have been affected. The inheritance pattern is shown here in a pedigree. What best describes this inheritance pattern?A)sex-linked on the YB)dominant trait on the XC)sex-linked recessive on the XD)dominant trait on an autosome

Answer 1

Hemophilia is caused by a recessive allele found in the X chromosome, so if a male has the defective gene, he will present the disease, because it's the only copy of the gene that he has.