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Ch. 4 - Extensions of Mendelian Genetics
Klug - Concepts of Genetics 12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
All textbooksKlug 12th EditionCh. 4 - Extensions of Mendelian GeneticsProblem 17a
Chapter 4, Problem 17a

In rats, the following genotypes of two independently assorting autosomal genes determine coat color:
Genotype and phenotype combinations for coat color in rats, including gray, yellow, black, and cream.
A third gene pair on a separate autosome determines whether or not any color will be produced. The CC and Cc genotypes allow color according to the expression of the A and B alleles. However, the cc genotype results in albino rats regardless of the A and B alleles present. Determine the F₁ phenotypic ratio of the following crosses:
AAbbCC×aaBBcc

Verified step by step guidance
1
Identify the genotypes of the parents for all three gene pairs: Parent 1 is AAbbCC and Parent 2 is aaBBcc.
Determine the possible gametes each parent can produce based on their genotypes: Parent 1 can produce gametes with A b C alleles, and Parent 2 can produce gametes with a B c alleles.
Combine the gametes from each parent to find the F₁ offspring genotypes: all offspring will have genotype AaBbCc.
Analyze the effect of the third gene (C locus) on coat color: since all offspring have at least one C allele (Cc), color will be expressed according to the A and B alleles.
Use the A and B alleles in the offspring (AaBb) to determine the phenotype based on the given dominance relationships: A–B– results in gray coat color.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Independent Assortment of Genes

Independent assortment refers to the principle that genes located on different chromosomes segregate independently during gamete formation. This means the inheritance of one gene does not affect the inheritance of another, allowing for new combinations of alleles in offspring. In this question, the A, B, and C genes assort independently, influencing coat color phenotypes.
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Gamete Genetics and Independent Assortment

Epistasis and Gene Interaction

Epistasis occurs when one gene masks or modifies the expression of another gene. Here, the C gene controls whether color is produced at all; the cc genotype causes albinism regardless of A and B alleles. This is an example of recessive epistasis, where the homozygous recessive genotype at one locus masks the effects of other loci.
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Interacting Genes Overview

Genotype to Phenotype Mapping

Understanding how specific genotypes translate into phenotypes is crucial. The A and B genes determine coat color combinations (gray, yellow, black, cream) based on dominant and recessive alleles, while the C gene controls color presence. Correctly interpreting these relationships allows prediction of offspring phenotypes from parental genotypes.
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Mapping with Markers
Related Practice
Textbook Question

Pigment in mouse fur is only produced when the C allele is present. Individuals of the cc genotype are white. If color is present, it may be determined by the A, a alleles. AA or Aa results in agouti color, while aa results in black coats. In three crosses between agouti females whose genotypes were unknown and males of the aacc genotype, the following phenotypic ratios were obtained:

(1) 8 agouti

(2) 9 agouti

(3) 4 agouti, 8 white 10 black, 5 black, 10 white

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Textbook Question

With reference to the eye color phenotypes produced by the recessive, autosomal, unlinked brown and scarlet loci in Drosophila, predict the F₁ and F₂ results of the following P₁ crosses. (Recall that when both the brown and scarlet alleles are homozygous, no pigment is produced, and the eyes are white.)

Brown x White

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Textbook Question

In rats, the following genotypes of two independently assorting autosomal genes determine coat color:

A third gene pair on a separate autosome determines whether or not any color will be produced. The CC and Cc genotypes allow color according to the expression of the A and B alleles. However, the cc genotype results in albino rats regardless of the A and B alleles present. Determine the F₁ phenotypic ratio of the following crosses:

AaBbCc×AaBbcc

472
views
Textbook Question

In rats, the following genotypes of two independently assorting autosomal genes determine coat color:

A third gene pair on a separate autosome determines whether or not any color will be produced. The CC and Cc genotypes allow color according to the expression of the A and B alleles. However, the cc genotype results in albino rats regardless of the A and B alleles present. Determine the F₁ phenotypic ratio of the following crosses: AaBBCc×AaBBCc

760
views
Textbook Question

Pigment in mouse fur is only produced when the C allele is present. Individuals of the cc genotype are white. If color is present, it may be determined by the A, a alleles. AA or Aa results in agouti color, while aa results in black coats. What F₁ and F₂ genotypic and phenotypic ratios are obtained from a cross between AACC and aacc mice?

756
views
Textbook Question

In rats, the following genotypes of two independently assorting autosomal genes determine coat color:

A third gene pair on a separate autosome determines whether or not any color will be produced. The CC and Cc genotypes allow color according to the expression of the A and B alleles. However, the cc genotype results in albino rats regardless of the A and B alleles present. Determine the F₁ phenotypic ratio of the following crosses:

AABbCc×AABbcc

1474
views