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More problems of genetic inheritance of a character. (Page 5)

Genetics problem 26

In the pea (Pisum sativum), the long stem (tall plant) is dominant over the short stem (dwarf plant). If a plant homozygous for the dominant trait is crossed with a dwarf plant, indicate the genotypes, phenotypes and proportions of the offspring of the crossing of an F1 plant with the long-stemmed parent.

Indicate the genotypes, phenotypes and proportions of the offspring from the crossing of an F1 plant with a dwarf plant.

List the genotypes, phenotypes, and proportions of the offspring of two heterozygous plants. Reason for the answers.

Genetics problem 27

In cattle, the absence of horns (H) is dominant over the presence of horns (h). A bull without horns crossed with two cows. With cow A, which had horns, he had a calf without horns; with cow B, which had no horns, he had a calf with horns. What are the genotypes of the bull and cows A and B? Indicate the proportions of genotypes and phenotypes that would be expected in the offspring of the two crosses.

Genetics problem 28

In cows, the black color of the hair is determined by a recessive allele (b) while the white color is determined by the dominant allele (B). The milk production of white cows is much higher than that of black cows. To avoid having more black cows the farmer needs to know which of the white cows are carriers of the recessive allele. Suggest and explain a cross that allows the farmer to know which white cows are carriers of the recessive allele. Give reasons for the answer.

Genetics problem 29

A brown mink had children with a silver mink, all being brown. When these brown minks were crossed with each other they produced 47 brown minks and 15 silver minks. Determine all genotypes and phenotypes, and their relative proportions, in the F1 and F2 generations.

Genetics problem 30

A black-haired guinea pig whose parents are one black-haired and the other white-haired, is crossed with another white-haired guinea pig whose parents are both black-haired. Indicate what the genotypes of all of them and those of their descendants will be like.

Genetic problem 31

A pair of black-haired mice has a white-haired offspring. This one is crossed with a female with black hair, whose parents were one with black hair and another with white hair, but they never had white-haired offspring.
It indicates the genotype of all of them and that of their descendants (the white allele is recessive).

Genetics problem 32

The R gene that governs curly hair dominates over the recessive (r) gene for straight hair. A woman with curly hair marries a man with straight hair and they have a daughter with curly hair. The woman's father had straight hair, they do not remember that of the mother, but they do know that the maternal grandmother had it straight and the maternal grandfather had it curly, although his mother's was straight. What is the genotype of all of them?

Genetics problem 33

a) Briefly explain the type of inheritance of a hereditary disease suffered by a man whose parents do not manifest the disease. List the genotypes of the parents and the child.

b) Can a couple in which both members have a dominant inherited disease have a healthy offspring? Reason for the answer indicating the genotypes and phenotypes of the parents and the offspring.

Genetics problem 34

In peas, the gene that expresses the yellow color (A) is dominant over the one that expresses the green color (a). How likely is it to get green peas in the second generation from the cross between hybrid yellow peas and purebred yellow peas?

Genetics problem 35

The guinea pig hair color character is N: black, dominant, and n: white. Find out which are the parents that cause the respective F1.
     a) 1/4 NN, ½ Nn, 1/4 nn
     b) ½ Nn, ½ nn
     c) All Nn


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