In chickens, the presence of feathers on the legs is due...

Question

In chickens, the presence of feathers on the legs is due to a dominant allele (F), and the absence of leg feathers is due to a recessive allele (f). The comb on the top of the head can be either pea-shaped, a phenotype that is controlled by a dominant allele (P), or a single comb controlled by a recessive allele (p). The two genes assort independently. Assume that a pure-breeding rooster that has feathered legs and a single comb is crossed with a pure-breeding hen that has no leg feathers and a pea-shaped comb. The F₁ are crossed to produce the F₂. Among the resulting F₂, however, only birds with a single comb and feathered legs are allowed to mate. These chickens mate at random to produce F₃ progeny. What are the expected genotypic and phenotypic ratios among the resulting F₃ progeny?

Accepted Answer

Hi, everyone. Let's take a look at this practice problem together in a fish, gold skin color. Capital G is dominant to black skin color, lowercase G and split tail fin. Capital S is dominant to single tail fin. Lowercase S A breeder crosses a male fish having capital G, lowercase G capital S lowercase S genotype with a female fish having lowercase G lowercase G capital S lowercase S genotype determine the expected phenotypic ratio of the progeny. The answer options are a 3 to 1, B 9 to 7, C, 3 to 1 to 3 to 1 or D 9 to 3 to 3 to 1. We will solve this problem using a pennant square first by determining the progeny genotype and then using that to determine their phenotype. Now, the first step is to determine the possible a little combinations that the male fish and the female fish can pass on in games. We can use smaller pundit squares to determine this. Now, the male fish genotype is capital G, lowercase G capital S lowercase S. The pun square analysis to determine his possible gametes produced are on the screen. The skin color ails are in the top row and the tail ails are in the first column, analyzing the puit square. He will produce gas capital G capital S capital G, lowercase S, lowercase G capital S and lowercase G lowercase S. Now let's repeat the same process for the female fish. Her genotype is lowercase G, lowercase G capital S lowercase S. The pundit square analysis to determine her possible gametes are uh is on the screen again, the skin color ails are it filled in the top row? And the tail of lies are in the first column. She produces gas, lowercase G capital S, lowercase G, lowercase S, lowercase G, capital S and lowercase G lowercase S. Now we can use the possible gas to fill out a pundit square. We'll put the possible male gametes on the top row of the pundit square and the possible female gametes in the first column. I'm about to post the results on the screen. However, I would encourage you to pause and practice filling this out on your own. So the results of that cross are on your screen. So the cross gave us all the possible genotypes. Now, we need to analyze these genotypes and determine the phenotypes. Now, there are four different phenotypes. So let's review them. The possible phenotypes. There are six offspring with gold and split tail fin. They are highlighted in orange, two with gold skin and single tail fin highlighted in purple, six offspring with black and split tail fin, they are highlighted in green and two offspring with black and single tail fin and they are highlighted in blue. So the phenotypic ratio is 6 to to 6 to 2. And if we simplify that, that ratio now becomes 3 to 1 To 3 - one. Therefore, the correct answer is option C 3 to 1 to 3 to 1. All right, everyone. I hope you found this helpful and I'll see you soon for the next practice problem.

Key Concepts

Mendelian Genetics

Independent Assortment

Genotypic and Phenotypic Ratios

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