C.

Nil

When a colour blind (X^CY) marries to a woman with normal sight (XX) who has no family history of colour blindness, all of their sons will be normal pure and all of their daughters will be carriers as shown below:

So in the next generation, the children of all of their son will be normal in all conditions(except the case in which the wife involved is not carrier neither colour blind). For carrier daughters.
(i) If they many to a normal man 50% of their grandsons will become colour blind as

(ii) If carrier daughter marries to a colour blind man 50% of their grandson will be colour blind along with 50% of the grand daughter while rest 50% of the grand daughters will be carriers as

So in both the above cases, the result shows 50% of grand sons will be colour blind which in terms of over all progress (son + daughter) comes as 25% thus confirming the probability as 0.25.

D.

crossing of one F₁ progeny with male parent

Test cross, crossing of F₁ progeny to the recessive parent is used to find the genotype of the progeny.

A.

Down's syndrome

Down’s syndrome is caused by non-disjunction of 21st chromosome

D.

both alleles independently expressed in the heterozygote

A gene shows codominance when both alleles in heterozygous condition, express their traits independently instead of showing dominant-recessive relationship and such alleles are called codominant alleles. 

A.

has 45 chromosomes with XO

Turner syndrome is a chromosomal condition that affects the development in females. The most common feature of Turner syndrome is short stature, which becomes evident by the age of about 5. An early loss of ovaries develop normally at first, but egg cells usually die prematurely and most ovarian tissue degenerates before birth. In other words, the absence of one of the X - chromosome i.e., 45 with XO (or 44 + XO).