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Ch. 14 - Mendel and the Gene
All textbooksFreeman 8th EditionCh. 14 - Mendel and the GeneProblem 4
Chapter 14, Problem 4

Two black female mice are crossed with a brown male. In several litters, female I produced 9 black offspring and 7 brown; female II produced 57 black offspring. What deductions can you make about the inheritance of black and brown coat color in mice? What are the genotypes of the parents?

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Determine the dominant and recessive traits: In this scenario, black coat color appears more frequently than brown, suggesting that black is the dominant trait (B) and brown is the recessive trait (b).
Analyze the offspring of female I: Since female I produced both black and brown offspring when crossed with a brown male, she must be heterozygous (Bb) to be able to pass on the recessive brown allele (b).
Consider the genotype of the brown male: The brown male must be homozygous recessive (bb) because brown is the recessive trait.
Analyze the offspring of female II: Female II produced only black offspring. Given that the male is brown (bb), female II must also be heterozygous (Bb) to consistently produce black offspring, which means she carries one dominant allele (B).
Conclude the genotypes: Female I is Bb, Female II is Bb, and the brown male is bb. This explains the observed offspring colors and their ratios.

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Key Concepts

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

Mendelian Inheritance

Mendelian inheritance refers to the principles of heredity established by Gregor Mendel, which include the concepts of dominant and recessive traits. In this case, the black coat color is likely dominant over the brown coat color. Understanding these principles helps in predicting the offspring's phenotypes based on the genotypes of the parents.
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Polygenic Inheritance

Genotype and Phenotype

The genotype is the genetic makeup of an organism, while the phenotype is the observable physical characteristics. In this scenario, the black and brown coat colors represent different phenotypes, which arise from specific genotypes. Identifying the genotypes of the parent mice is crucial for understanding the inheritance patterns of their offspring.
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Punnett Square

A Punnett square is a diagram used to predict the genetic outcomes of a cross between two organisms. It helps visualize the possible combinations of alleles from the parents, allowing for the determination of expected ratios of offspring phenotypes. This tool is essential for analyzing the inheritance patterns observed in the litters of the crossed mice.
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Related Practice
Textbook Question

The genes for the traits that Mendel worked with are either all located on different chromosomes or behave as if they were. How did this help Mendel recognize the principle of independent assortment? a. Otherwise, his dihybrid crosses would not have produced a 9 : 3 : 3 : 1 ratio of F2 phenotypes. b. The occurrence of individuals with unexpected phenotypes led him to the discovery of recombination. c. It led him to the realization that the behavior of chromosomes during meiosis explained his results. d. It meant that the alleles involved were either dominant or recessive, which gave 3 : 1 ratios in the F1 generation.

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Textbook Question

Why is the pea wrinkle-seed allele a recessive allele? a. It 'recedes' in the F2 generation when homozygous parents are crossed. b. The trait associated with the allele is not exhibited in heterozygotes. c. Individuals with the allele have lower fitness than that of individuals with the dominant allele. d. The allele is less common than the dominant allele. (The wrinkled allele is a rare mutant.)

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Textbook Question

The alleles found in haploid organisms cannot be dominant or recessive. Why? a. Dominance and recessiveness describe which of two possible phenotypes are exhibited when two different alleles occur in the same individual. b. Because only one allele is present, alleles in haploid organisms are always dominant. Ac. lleles in haploid individuals are transmitted like mitochondrial DNA or chloroplast DNA. d. Most haploid individuals are bacteria, and bacterial genetics is completely different from eukaryotic genetics.

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Textbook Question

A plant with orange, spotted flowers was grown in the greenhouse from a seed collected in the wild. The plant was self-pollinated and gave rise to the following progeny: 88 orange with spots, 34 yellow with spots, 32 orange with no spots, and 8 yellow with no spots. What can you conclude about the dominance relationships of the alleles responsible for the spotted and unspotted phenotypes? What can you conclude about the genotype of the original plant that had orange, spotted flowers?

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Textbook Question

In peas, purple flowers are dominant to white. If a purple-flowered, heterozygous plant were crossed with a white-flowered plant, what is the expected ratio of genotypes and phenotypes among the F1 offspring? If two of the purple-flowered F1 offspring were randomly selected and crossed, what is the expected ratio of genotypes and phenotypes among the F2 offspring?

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Textbook Question

In garden peas, yellow seeds (Y) are dominant to green seeds (y), and inflated pods (I) are dominant to constricted pods (i). Suppose you have crossed YYII parents with yyii parents. Draw the F1 Punnett square and predict the expected F1 phenotype(s).

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