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Problem solution for genetic mapping of linked genes

Problem 1

A female mouse with yellow-mottled fur, eye-ear reduction and regular teeth was mated to a male mouse with dark gray fur, normal eye-ear size and irregular teeth. The F1 females were all wild type, that is, dark gray fur, normal eye-ear size and regular teeth. The F1 males had yellow-mottled fur, eye-ear reduction and regular teeth. A cross of F1 females to F1 males produced the following offspring in the F2 generation.

Phenotype for Number of
Fur color Eye-Ear size Teeth Males Females
Dark Gray Normal Regular 11 142
Yellow Mottled Reduced Irregular 18 0
Dark Gray Reduced Irregular 47 0
Yellow Mottled Normal Regular 54 57
Dark Gray Reduced Regular 3 51
Yellow Mottled Normal Irregular 4 0
Yellow Mottled Reduced Regular 135 150
Dark Gray Normal Irregular 128 0

a. Draw a genetic map showing the distances between these genes.
b. Express the differences in map units.
c. What is the coefficient of coincidence?
d. What is the degree of interference?

Problem 2

A female rabbit with hemophilia, rickets, and a tail was mated to a male rabbit that did not have hemophilia or rickets but lacked a tail. The F1 females were all wild type, that is, no having hemophilia or rickets but having a tail. The F1 males had hemophilia, rickets, and tails. A cross of F1 females to F1 males produced the following offspring in the F2 generation:

Hemophilia Rickets Tails Males Females
Yes No No 5 0
No Yes Yes 3 84
Yes Yes No 30 0
No No Yes 27 160
Yes No Yes 86 91
No Yes No 81 0
Yes Yes Yes 128 165
No No No 140 0

a. What are the genotypes of the original parents?
b. Write Each genotype to show which alleles are linked together on the same chromosome.
c. What are the genotypes of the F1 males and females? Write each genotype to show which alleles are linked together on the same chromosome.
d. Draw a genetic map showing the distances between these genes. Express the distances in map units.
e. What is the degree of interference?

Solution Preview

The key to solving these two problems is to realize that all the traits listed for either problem are sex-linked, meaning that the genes are found on the X chromosome. This can be deduced because of the criss-cross pattern of inheritance seen when looking at the F1 generation. For example the females in problem one are yellow-mottled fur, eye-ear reduction and regular teeth. ...

Solution Summary

This solution contains step-by-step directions to walk you through solving a specific genetic problem focused on mapping of linked genes. Specifically, you will learn how to determine: the order of genes found on the same chromosome, the distance in map units between linked genes, the definition and how to determine the coefficient of coincidence, and the definition and how to determine interference. Additionally the problem provides explanation of how to determine all of this information when the genes are sex-linked genes found on the X chromosome. There are two problems, the first provides very detailed solutions to aid you in learning the process while the second is a similar problem with less detailed explanations to allow you to test your knowledge learned in the first problem.

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