In cocker spaniels, black coat color (B) is dominant over red (b), and solid color (S) is dominant over spotted (s).In the F₂ generation of a cross between BB ss with bb SS, what fraction of the offspring are expected to be black and spotted? A)1/16 B)9/16 C)1/9 D)3/16 E)3/4

Question

Quizplus · Accepted Answer

The parents can be represented as BBss and bbSS. When we cross them, we get F1 generation offspring with genotype BbSs (since B and S are dominant traits). When we cross the F1 generation offspring, we get the F₂ generation. To find the fraction of offspring that are black and spotted, we need to look at the genotype of the F2 generation offspring. We can use a Punnett square to do this: | | B | b | |---|---|---| | S | BS | bS | | s | Bs | bs | Each box represents a possible offspring genotype. We can see that there are 4 boxes out of 16 that have the genotype Bbss, which means they are black and spotted. Therefore, the fraction of offspring that are black and spotted is 4/16 or 1/4 or 0.25 or 25%. However, the question asks for the fraction in terms of the F₂ generation, so we need to account for the fact that the F2 generation offspring can have different combinations of Bs and bs alleles. Since both parents in the F₂ generation have the same genotype (BbSs), all of their offspring will inherit one B or b allele and one S or s allele from each parent. So each offspring has a 1/2 chance of inheriting a B allele and a 1/2 chance of inheriting an S allele. We can use the multiplication rule of probability to find the probability of offspring being black and spotted: P(BbsSs) = P(Bb) x P(sS) = (1/2) x (1/2) = 1/4 Therefore, the fraction of offspring that are black and spotted in the F₂ generation is also 1/4 or 0.25 or 25%. The correct answer is D) 3/16, which is not an option.

In Cocker Spaniels, Black Coat Color (B) Is Dominant Over