Question

"brown hair in dogs is controlled by a recessive allele b. black hair is controlled by a dominant allele B at the same locus. what is the probability of two heterozygotes producing a black puppy?

Answer 1

Answer:

Bb or BB = 75%

Explanation:

In order to solve this question we have to use the Punnett square.

The Punnett square demonstrate the genetic results when two individuals cross. In order to make the square, we have to draw a big square with small squares inside, each representing all possible combinations of alleles. Since we have 2 alleles we have 4 possible combinations, that means 4 small squares.

In the up part of the square we introduce the alleles of the parent 1 and in the left part the alleles of parent 2. The results will be written in the small squares.

The attached image represents the crossing of two heterozygotes Bb x Bb

Represented by red there's 25% of probability of the puppy be homozigot BB, that means he will be black.

Represented by green there's 50% of probability of the puppy be heterozigot Bb, that means he also will be black, since B is dominant.

Represented by blue there's 25% of probability of the puppy be homozigot bb. That means he will be brown, since there's no dominant B there.

Total: 25% (BB) + 50%(Bb) = 75% of being black