The scientists who have given the theory of linkage are

Drosophila flies with one half of the body male and other half female is referred to as

$A$ $Y-$linked gene is responsible for hypertrichosis (long hair on ears). When an affected man marries a normal woman, what percentage of their daughters would be expected to have hairy ears?

Barr body in mammals represents

Assertion : Phenylketonuria is a recessive hereditary disease caused by body’s failure to oxidize an amino acid phenylalanine to tyrosine, because of a defective enzyme.

Reason : It results in the presence of phenylalanine acid in urine.