If a colour-blind man marries a woman who is homozygous for normal colour vision, the probability of their son being colour-blind is

The mechanism that causes a gene to move from one linkage group to another is called

Which of the following most appropriately describes haemophilia ?

Pick out the correct statements :
(a) Haemophilia is a sex-linked recessive disease.
(b) Down's syndrome is due to aneuploidy.
(c) Phenylketonuria is an autosomal recessive gene disorder.
(d) Sickle cell anaemia is an X – linked recessive gene disorder.