In mammals, hair/fur color is determined by the expression of a number of differ

Question

In mammals, hair/fur color is determined by the expression of a number of different genes, each of which has two or more alleles. According to Mendels second law, unlinked genes (those that are either on different chromosomes or on the same chromosome but very distant from one another) assort independently because they align independently on the spindle during metaphase I of meiosis.

In this tutorial, you will solve genetics problems related to the inheritance of fur color in mice.

In mice, agouti fur is a dominant trait resulting in individual hairs having a light band of pigment on an otherwise dark hair shaft. A mouse with agouti fur is shown here, along with a mouse with solid color fur, which is the recessive phenotype (A = agouti; a = solid color).

A separate gene, which is not linked to the agouti gene, can result in either a dominant black pigment or a recessive brown pigment (B = black; b = brown).

A litter of mice from the mating of two agouti black parents includes offspring with the following fur colors:

solid color, black

solid color, brown (sometimes called chocolate)

agouti black

agouti brown (sometimes called cinnamon)

none

1/8

3/16

1/4

1/2

9/16

not enough information given

In addition to A and a, the agouti gene has a third allele, AY. Here is some information about the inheritance of the AYallele.

The AYallele is dominant to both A and a.

The homozygous genotype (AYAY) results in lethality before birth.

The heterozygous genotypes (AYA or AYa) result in yellow fur color, regardless of which alleles are present for the B/b gene. (This effect exhibited by the AYallele is known as epistasis--when the expression of one gene masks the expression of a second gene.)

Suppose you mate two mice with the genotypes AYaBb x AYaBb . Considering only the live-born offspring, what would be the expected frequency of mice with yellow fur? (For help getting started, see Hint below.) Answer must be in numeric form, no words. You may use fractions or decimal numbers.

Answer

Hint 1. How to approach this problem

To calculate the probability that a live-born offspring will have yellow fur, you need to consider this information.

The effect of epistasis: Because yellow fur color is epistatic, the genotype of the B/b gene will not affect the fur color of any offspring that inherits an AY allele. For this reason, you can ignore the B/bgene for this problem.

The effect of lethality: Because the AYA Y genotype is lethal, zygotes that receive that allele combination will not continue to develop. As a result, when you complete a Punnett square for the first gene of this cross (AYaBb x AYaBb), you need to disregard any offspring with the lethal allele combination. Only consider the remaining offspring in calculating the probability of yellow fur.

What would be the expected frequency of agouti brown offspring in the litter?

none

1/8

3/16

1/4

1/2

9/16

not enough information given

In mammals, hair/fur color is determined by the expression of a number of different genes, each of which has two or more alleles. According to Mendel??s second law, unlinked genes (those that are either on different chromosomes or on the same chromosome but very distant from one another) assort independently because they align independently on the spindle during metaphase I of meiosis. In this tutorial, you will solve genetics problems related to the inheritance of fur color in mice. In mice, agouti fur is a dominant trait resulting in individual hairs having a light band of pigment on an otherwise dark hair shaft. A mouse with agouti fur is shown here, along with a mouse with solid color fur, which is the recessive phenotype (A = agouti; a = solid color). Suppose you mate two mice with the genotypes AYaBb x AYaBb . Considering only the live-born offspring, what would be the expected frequency of mice with yellow fur? (For help getting started, see Hint below.) Answer must be in numeric form, no words. You may use fractions or decimal numbers. Answer Hint 1. How to approach this problem To calculate the probability that a live-born offspring will have yellow fur, you need to consider this information. The effect of epistasis: Because yellow fur color is epistatic, the genotype of the B/b gene will not affect the fur color of any offspring that inherits an AY allele. For this reason, you can ignore the B/bgene for this problem. The effect of lethality: Because the AYA Y genotype is lethal, zygotes that receive that allele combination will not continue to develop. As a result, when you complete a Punnett square for the first gene of this cross (AYaBb x AYaBb), you need to disregard any ??offspring?? with the lethal allele combination. Only consider the remaining offspring in calculating the probability of yellow fur. A litter of mice from the mating of two agouti black parents includes offspring with the following fur colors: solid color, black solid color, brown (sometimes called chocolate) agouti black agouti brown (sometimes called cinnamon) What would be the expected frequency of agouti brown offspring in the litter? none 1/8 3/16 1/4 1/2 9/16 not enough information given In addition to A and a, the ??agouti?? gene has a third allele, AY. Here is some information about the inheritance of the AYallele. The AYallele is dominant to both A and a. The homozygous genotype (AYAY) results in lethality before birth. The heterozygous genotypes (AYA or AYa) result in yellow fur color, regardless of which alleles are present for the B/b gene. (This effect exhibited by the AYallele is known as epistasis--when the expression of one gene masks the expression of a second gene.) A separate gene, which is not linked to the agouti gene, can result in either a dominant black pigment or a recessive brown pigment (B = black; b = brown).

Explanation / Answer

Answer:

Part A: To find expected frequency of agouti brown offspring in the litter.

Given Parental Phenotype: Agouti Black

Possible Parental Genotypes: AABB, AaBb, AABb, AaBB

For all possible combination of parental genotype only mating between AaBb * AaBb would result in production of offspring with all the four given phenotype ie.

solid color, black

solid color, brown (sometimes called chocolate)

agouti black

agouti brown (sometimes called cinnamon)

Punett square to to predict an outcome of a cross between AaBb * AaBb

Parents :             AaBb         *            AaBb

Gametes   :     AB Ab aB ab          AB Ab aB ab

Frequency of offspring with agouti brown fur in the litter: number of offspring with agouti brown fur / total number of offsprings

                                                                              : 3 / 16

Part B: To find expected frequency of mice with yellow fur

Parents : Ay aBb       *            AyaBb

Gametes: AyB   Ayb   aB   ab           AyB   Ayb aB   ab

Based on given hints

Frequecy of offspring with yellow fur : number of offsprings with yellow fur / total number of alive offsprings

: 8 / 16

: 2 / 3                                                                        

AB Ab aB ab AB ABAB AbAB aBAB abAB Ab ABAb AbAb aBAb abAb aB ABaB AbaB aBaB abaB ab ABab Abab aBab abab

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