If a modified allele produces a non-functional enzyme or no enzyme,then the phenotype will not be affected in which of the following cases?

Blood group of a person is $A$ and he is suffering from albinism. What percentage of his gametes will have genotype $I^A a$?

Genes that are similar in phenotypic effect when present separately,but together interact to produce a different trait and the ratio is $9:7$ in the $F_2$ generation. What are such genes known as?

Which of the following structures is identical in monozygotic twins?

Pick out the correct statements.
$I.$ Haemophilia is a sex-linked recessive disease
$II.$ Down's syndrome is due to aneuploidy
$III.$ Phenylketonuria is an autosomal dominant gene disorder
$IV.$ Phenylketonuria is an autosomal recessive gene disorder
$V.$ Sickle cell anaemia is an $X$-linked recessive gene disorder

Which of the following is $NOT$ true for $Drosophila$ $melanogaster$?