In Dexter and Kerry cattle, animals may be polled (hornless) or horned. The Dexter animals have short legs, whereas the Kerry animals have long legs. When many offspring were obtained from matings between polled Kerrys and horned Dexters, half were found to be polled Dexters and half polled Kerrys. When these two types of F₁ cattle were mated to one another, the following F₂ data were obtained:
3/8 polled Dexters
3/8 polled Kerrys
1/8 horned Dexters
1/8 horned Kerrys
A geneticist was puzzled by these data and interviewed farmers who had bred these cattle for decades. She learned that Kerrys were true breeding. Dexters, on the other hand, were not true breeding and never produced as many offspring as Kerrys. Provide a genetic explanation for these observations.

Question

In Dexter and Kerry cattle, animals may be polled (hornless) or horned. The Dexter animals have short legs, whereas the Kerry animals have long legs. When many offspring were obtained from matings between polled Kerrys and horned Dexters, half were found to be polled Dexters and half polled Kerrys. When these two types of F₁ cattle were mated to one another, the following F₂ data were obtained:

3/8 polled Dexters

3/8 polled Kerrys

1/8 horned Dexters

1/8 horned Kerrys

A geneticist was puzzled by these data and interviewed farmers who had bred these cattle for decades. She learned that Kerrys were true breeding. Dexters, on the other hand, were not true breeding and never produced as many offspring as Kerrys. Provide a genetic explanation for these observations.

Accepted Answer

Hi everyone, welcome back. Here's our next question. If curly for big C. Is dominant over straight for little C. And the coat color. Black Bigby is dominant over the color. Brown, little B. And dogs determine the probability of puppies with curly fur and a black coat color. When two big B. Little B. Big C. Little C. Parent dogs are crossed. So we'll assume that these are independently a sorting out on the same chromosome and not sex linked. Um And so since our problem doesn't tell us otherwise and it's not one of those widely known um traits that have those characteristics. We're looking at a cross between parents that are hetero zygotes in two different traits. So we're looking at a di hybrid cross in this case and that means we can kind of approach this problem solving this problem in one of two different ways. Um If you can recall in your di hybrid costs, the fanatic ratio Of the offspring will be 9-3-3-1. Where these numbers refer to on the nine uh dominant in both traits, the two threes will be dominant for one trait recessive for the other and then the one would be recessive for both traits. Again, this is a good ratio to know to allow to solve problems like this very quickly. So we are looking for the probability of puppies with curly fur. So curly fur is the dominant trait And Black Coat, Black Coat would be dominant also. So these puppies are dominant in both traits. And in that case we're looking at a ratio of nine out of a total 16 outcomes. So our answer choice will be choice C9/16. Now there's another way we could have gone about solving this and we could have looked at what's the probability of each event. So if we just look at curly fur and we say we've got parents who are heterosexuals for that gene, Then we know our um ratio here for curly for would be 3-1 curly being dominant, two recessive. So the probability of curly for would be 3/4. And we would multiply that by the probability of black coat again that would be hetero parents. Giving us a ratio of 3 to 1. Black is also dominant. So that ratio will also be 3/4. So we multiply 3/4 by 3/4 since the probability of both events occurring is the product of the individual probabilities. And that will give us 9/16 as our probability of both events occurring. So that confirms our answer choice of C9/16. As the probability of puppies with curly fur and a black coat. See you in the next video

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Key Concepts

Epistasis and Gene Interaction

True Breeding and Homozygosity

Mendelian Inheritance and Segregation Ratios