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More problems of genetic inheritance of a character. (Page 7)

Genetics problem 46

They have given us a dozen mice, all black, and although we know they are of the same F1, they have not told us if the parents were pure breeds or what color they were. We have crossed them several times, and we have obtained a total of 125 mice, 93 black and 32 white. Assuming that the hair color character depends on a single gene with Mendelian inheritance:

a) What can we say about the character "white color" in relation to its dominance?

b) What can we deduce about the genotypes of our original dozen of mice?

c) What can we deduce regarding the genotypes and phenotypes of the two unknown parents?

d) If now one of the new white mice obtained is crossed with a black one, is there any possibility that one of the children has a white phenotype? Explain briefly.

Genetics problem 47

In mice, white hair dominates over black. Two white mice of the same genotype are crossed. The  offspring are made up of 75% white mice and 25% black mice. If A is the dominant allele  and it is the recessive allele, answer the following questions:

a) Genotypes of the individuals that are crossed.
b) Genotypes of the offspring's black and white mice.

Genetics problem 48

In cattle, the lack or presence of horns is a character determined by an autosomal gene with two alleles that present a dominance relationship. A bull without horns crossed with three cows. With cow A, which had horns, he had a calf without horns; with cow B, also with horns, he had a calf with horns; with cow C, which had no horns, he had a calf with horns. (2.5 points)

a) Is the presence of horns a dominant or recessive allele? Give reasons for the answer. (1.2 points)

b) What is the genotype of each individual? (0.7 points)

c) What other offspring, and in what proportions, would one expect from these crosses? (0.6 points)

Genetics problem 49

The black color of the hair of a variety of mouse depends on the dominant allele "A" and the white color  of its recessive allele "a". Answer the following questions reasonably:

a)  Knowing the genotype of all individuals can their phenotypes also be known? [0.5];

b) knowing the phenotype of all individuals can their genotypes be known? [0.5].

Genetics problem 50

In a certain breed of dog, the hair color (black or white) is a character determined by an autosomal gene with two alleles that have a dominance relationship. A breeder observes that, by making the following crosses, he obtains the pups shown in the table: (2 points)

Female Male Young
Junction 1 Krispy (white) Muasé (black) Two black and two white females
Three black and three white males
Junction 2 Coucou (black) Muasé (black) Four black and one white females
Three black males and one white
Junction 3 Lupita (white) Muasé (black) Three black and three white females
Two black and two white males

a) Is the allele that produces the color black dominant or recessive? Justify your answer by indicating all the genotypes of the animals involved in the different crosses. (1 point)
b) Given this dominance relationship, check by the observed crosses if this gene could be linked to the X chromosome (1 point)

Genetics problem 51

The absence of molars in the human species is due to an autosomal dominant gene. A couple, both without molars, have a daughter with molars.

a.- Indicates the genotypes of all members of this family.
b.- What is the probability that the couple have another descendant with molars?
c.- What is the proportion of possible heterozygotes in your offspring?

Genetics problem 52

Regarding Mendel's contributions to the study of heredity:

a) In goats, the absence of "A" horns is dominant over the "a" allele for the presence of horns. Suppose a male without horns is crossed with three females: female 1 with horns, from which a young is born. with horns; female 2 with horns, from which a calf without horns is born; and female 3 without horns, from which a calf with horns is born. Indicate the genotype of the four parents: male, female 1, female 2 and female 3 (1 point).

b) What type of crossover could be designed to distinguish a dominant homozygous (AA) from a heterozygous (Aa) individual? Give reasons for the answer. What denomination does it receive? (1 point).

Genetics problem 53

Retinitis pigmentosa is a degenerative disease that can lead to blindness. Several genes are involved and, depending on what these genes are, the inheritance can be: autosomal dominant, autosomal recessive, or sex-linked recessive. A couple, both of whom are affected by retinitis pigmentosa, have two sons, one of whom has disease and the other does not. 

a) Which of the three types of inheritance of retinitis pigmentosa is possible in this case? Which is why it can't be either of the other two types of inheritance. List the genotypes of all cases. 

b) Indicate the probabilities that the couple's two children, in turn, do not have affected descendants if their respective partners are not. 

IMPORTANT: Indicate which symbol you use for each of the two alleles in each case.

Genetics problem 54

Fatal familial insomnia (IFF) is a human disease due to a mutation in an R gene located on chromosome 20. The disease shows a dominant inheritance. A couple, both with the disease, have a daughter who does not have it. List the genotypes of all members of this family. Can a healthy daughter transmit the disease? What is the probability that this couple will have a healthy male child? And that he has a daughter with the disease? Reason for the answers.

Genetics problem 55

Regarding Mendel's contributions to the study of heredity:

In one breed of rabbits, short "A" hair is dominant over long "a" hair. Four crosses are carried out that give rise to the following percentages of phenotypes in their progeny:

Parental Progeny
one short hair x long hair 50% short hair and 50% long hair
two long hair x long hair 100% long hair
3 short hair x long hair 100% short hair
4 short hair x short hair 100% short hair

Indicate the possible genotypes of the parents and progeny of each of the crosses (1 point).


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