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To know genotypes and interference through gene map

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Three loci, mitochondrial malate dehydrogenase that forms a and b (MDHa, MDHb), glucouronidase that has forms 1 and 2 (GUS1, GUS2), and a histone gene that has + and - variants(H+, H-), are located on chromosome #7 in humans. Assume that the MDH locus is at position 35, GUS at position 45, and H at position 75. A female whose mother was homozygous for MDHa, GUS2, and H+ and whose father was homozygous for MDHb, GUS1, and H- produces a sample of 1000 egg cells. Give the genotypes and expected numbers of the various types of cells she would produce. Assume no chromosomal interference.

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Solution Summary

Since, the MDH locus is at position 35, GUS at position 45, and H at position 75, GUS is in between MDH & H.
Distance between MDH & GUS = 10 map unit
Distance between GUS & H = 30 map unit.

Since % recombinants = map distance
Hence, for gene MDHa & GUS2 locus :
10 = No. of recombinants for crossing over between MDHa & GUS2 / 1000 * 100
Or, No. of recombinants for crossing over between MDHa & GUS2 = 100

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Genetic problems regarding gene 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?

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