Black fur in mice (b) is dominant to brown fur (b). short tails (t) are dominant to long tails (t). the genes for the two traits are non-linked. what fraction of the progeny of crosses bbtt × bbtt will be expected to have black fur and long tails?

One half of the progeny would have black fur and long tail.

Explanation:  Given P1 BbTt x BBtt

Gametes according to segregation law are  1/2 BB, 1/2 Bb and 1/2 Tt, 1/2 tt

The F1  then: 1/4 BBTt, 1/4 BBtt, 1/4BbTt, 1/4 Bbtt.

So finally we obtain the result for the phenotype. The 50% of the mice are black and have long tails.

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