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 \(\mathrm{F}_{1}\) cattle were mated to one another, the following \(\mathrm{P}_{2}\) data were obtained: \(3 / 8\) polled Dexters \(1 / 8\) horned Dexters \(3 / 8\) polled Kerrys \(1 / 8\) 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.

Short answer

Answer: The proposed genetic explanation for the observed ratios in the F2 generation is that polled Kerrys have a dominant allele for the polled (hornless) trait and a dominant allele for the long legs trait, while Dexters have a recessive allele for the horned trait and a dominant allele for the short legs trait. The true-breeding nature of Kerrys results from them being homozygous dominant for both polled and long legs traits, and the non-true-breeding nature of Dexters, along with a genetic factor causing reduced offspring viability, can explain the difference in offspring numbers between Dexters and Kerrys.

Step-by-step solution

Understand the Initial Cross

First, we need to understand that polled Kerrys are crossed with horned Dexters. As a result, half of the offspring were found to be polled Dexters, and half polled Kerrys.

Determine the \(\mathrm{F}_{1}\) Cattle Types

From the initial cross, two types of \(\mathrm{F}_{1}\) cattle are obtained: polled Dexters and polled Kerrys.

Analyze the \(\mathrm{F}_{2}\) Generation

When these two types of \(\mathrm{F}_{1}\) cattle are mated with one another, the following data are obtained for the \(\mathrm{F}_{2}\) generation: - \(3 / 8\) polled Dexters - \(1 / 8\) horned Dexters - \(3 / 8\) polled Kerrys - \(1 / 8\) horned Kerrys This information indicates that there are specific genetic factors affecting the ratios of the cattle types in the \(\mathrm{F}_{2}\) generation.

Consider True-Breeding Traits

Recall that Kerrys are true-breeding, which means they consistently pass on specific traits to their offspring. Dexters, however, are not true-breeding and have less offspring than Kerrys. This information is crucial to understanding the genetic explanation for these observations.

Propose a Genetic Explanation

We can propose that Kerrys have a dominant allele for the polled (hornless) trait and a dominant allele for the long legs trait, while Dexters have a recessive allele for the horned trait and a dominant allele for the short legs trait. The true-breeding nature of Kerrys would result from them being homozygous dominant (having two copies of the dominant allele) for both polled and long legs traits. The smaller number of offspring from Dexters could be due to a genetic factor that causes some of the potential offspring to be non-viable during development, leading to fewer overall offspring.

Conclusion

Considering the provided data and true-breeding information of Kerrys, we propose that polled Kerrys and polled Dexters have specific genetic factors (dominant/recessive alleles) that affect the inheritance of certain traits such as horn status and leg length. These genetic factors and the true-breeding nature of Kerrys can lead to the observed ratios in the \(\mathrm{F}_{2}\) generation, while the non-true-breeding nature of Dexters, accompanied by a genetic factor causing reduced offspring viability, can explain the difference in offspring numbers between Dexters and Kerrys.