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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 4
Chapter 4, Problem 4

In foxes, two alleles of a single gene, P and p, may result in lethality (PP), platinum coat (Pp), or silver coat (pp). What ratio is obtained when platinum foxes are interbred? Is the P allele behaving dominantly or recessively in causing (a) lethality; (b) platinum coat color?

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1
Identify the genotypes and their associated phenotypes: PP results in lethality, Pp results in platinum coat, and pp results in silver coat.
Set up a Punnett square for the cross between two platinum foxes, both with genotype Pp.
Fill in the Punnett square to find the genotypic ratios of the offspring: PP, Pp, and pp.
Translate the genotypic ratios into phenotypic ratios, considering that PP individuals are lethal and will not survive.
Analyze the phenotypic outcomes to determine if the P allele is dominant or recessive for (a) lethality and (b) platinum coat color by observing which phenotypes appear in heterozygotes.

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Key Concepts

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

Mendelian Inheritance and Allele Interactions

Mendelian inheritance describes how alleles segregate and assort during reproduction, producing predictable genotype and phenotype ratios. Understanding dominant, recessive, and lethal alleles helps explain how different allele combinations affect traits and survival, such as when homozygous genotypes cause lethality.
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Lethal Alleles and Their Effects

Lethal alleles cause death when present in certain genotypes, often homozygous. They reduce or eliminate specific genotypes from offspring ratios, altering expected Mendelian ratios. Recognizing lethality is crucial to interpreting deviations in phenotypic ratios from typical dominant-recessive patterns.
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Dominance Relationships in Phenotypic Expression

Dominance refers to how one allele masks the effect of another in heterozygotes. An allele is dominant if it determines the phenotype when present, and recessive if its effect appears only in homozygotes. Determining dominance for traits like coat color or lethality involves analyzing offspring phenotypes from specific crosses.
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Related Practice
Textbook Question

The discussion centers on extensions and modifications of Mendelian principles and ratios. In the process, we encountered many opportunities to consider how this information was acquired. On the basis of these discussions, what answers would you propose to the following fundamental questions?

For genes whose expression seems to be tied to the sex of individuals, how do we know whether a gene is X-linked in contrast to exhibiting sex-limited or sex-influenced inheritance?

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Textbook Question
Write a short essay that explains why multiple and lethal alleles often result in a modification of the classic Mendelian monohybrid and dihybrid ratios.
456
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Textbook Question

In shorthorn cattle, coat color may be red, white, or roan. Roan is an intermediate phenotype expressed as a mixture of red and white hairs. The following data were obtained from various crosses:

How is coat color inherited? What are the genotypes of parents and offspring for each cross?

1512
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Textbook Question
In mice, a short-tailed mutant was discovered. When it was crossed to a normal long-tailed mouse, 4 offspring were short-tailed and 3 were long-tailed. Two short-tailed mice from the F1 generation were selected and crossed. They produced 6 short-tailed and 3 long-tailed mice. These genetic experiments were repeated three times with approximately the same results. What genetic ratios are illustrated? Hypothesize the mode of inheritance and diagram the crosses.
1113
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Textbook Question
List all possible genotypes for the A, B, AB, and O phenotypes. Is the mode of inheritance of the ABO blood types representative of dominance, recessiveness, or codominance?
1583
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Textbook Question

With regard to the ABO blood types in humans, determine the genotype of the male parent and female parent shown here:

Male parent: Blood type B; mother type O

Female parent: Blood type A; father type B

Predict the blood types of the offspring that this couple may have and the expected proportion of each.

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