In poodles, black fur is dominant to white fur. A black poodle is crossed with a white poodle. In a litter of four, all of the puppies are black. What is the BEST conclusion?

The black poodle is true breeding (homozygous) for the black fur colour.

Explanation:

Let the allele for fur colour be represented by B.

Black fur (B) is dominant over white fur (b).

Black poodle (B _) is crossed with white poodle (bb):

B _ x bb

Progeny (all black) = Bb, Bb, _b and _b.

Since all the progeny are black, _b = Bb (remember, B is dominant over b)

Hence, B_ is also BB.

The best conclusion is that the black poodle is true breeding (homozygous) for the black fur colour.

Explanation: all the puppies in the F1 generation are black because homozygous black (BB) is crossed with a homozygous white (bb) and since the black fur is dormant all the puppies will be black ie heterozygous black (Bb).