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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 32
Chapter 4, Problem 32

Predict the F₁ and F₂ results of crossing a male fowl that is cock-feathered with a true-breeding hen-feathered female fowl. Recall that these traits are sex limited.

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Understand the genetic basis of the traits: Cock-feathering and hen-feathering are sex-limited traits in fowl, meaning their expression depends on the sex of the individual. These traits are controlled by a single gene with two alleles, where the cock-feathering allele (C) is dominant in males but recessive in females, and the hen-feathering allele (H) is dominant in females.
Determine the genotypes of the parents: A true-breeding hen-feathered female must have the genotype HH (homozygous for the hen-feathering allele). A cock-feathered male must have the genotype CH, as cock-feathering is expressed in males when they carry at least one C allele.
Set up the Punnett square for the F₁ generation: Cross the male (CH) with the female (HH). Write the possible gametes for each parent. The male can produce gametes with either C or H alleles, while the female can only produce gametes with the H allele.
Predict the F₁ offspring: Combine the gametes from the Punnett square. The possible genotypes of the F₁ offspring are CH and HH. Since these traits are sex-limited, interpret the phenotypes based on the sex of the offspring. Male offspring with CH will be cock-feathered, while female offspring with CH will be hen-feathered. HH offspring will be hen-feathered regardless of sex.
Set up the Punnett square for the F₂ generation: Cross two F₁ individuals (e.g., CH x CH). Write the possible gametes for each parent (C and H for both). Combine the gametes to determine the genotypes of the F₂ offspring. Interpret the phenotypes based on the sex of the offspring, considering the sex-limited nature of the traits.

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Key Concepts

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

Sex-Linked Traits

Sex-linked traits are characteristics that are associated with genes located on sex chromosomes. In many species, including fowl, certain traits are expressed differently in males and females due to the presence of these genes on the X or Z chromosomes. Understanding how these traits are inherited is crucial for predicting offspring phenotypes in sex-limited inheritance.
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True-Breeding

True-breeding refers to organisms that consistently pass down specific phenotypic traits to their offspring when mated with another true-breeding organism of the same phenotype. In this context, a true-breeding hen-feathered female fowl will produce only hen-feathered offspring when crossed with another true-breeding individual of the same type, providing a baseline for predicting the F₁ generation.
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Punnett Square

A Punnett square is a diagram used to predict the genotypes and phenotypes of offspring from a genetic cross. By organizing the alleles of the parents, it allows for a visual representation of possible combinations in the F₁ and F₂ generations. This tool is essential for understanding inheritance patterns, especially in cases involving sex-limited traits.
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Related Practice
Textbook Question

Discuss the topic of phenotypic expression and the many factors that impinge on it.

Textbook Question

Two mothers give birth to sons at the same time at a busy urban hospital. The son of mother 1 is afflicted with hemophilia, a disease caused by an X-linked recessive allele. Neither parent has the disease. Mother 2 has a normal son, despite the fact that the father has hemophilia. Several years later, couple 1 sues the hospital, claiming that these two newborns were swapped in the nursery following their birth. As a genetic counselor, you are called to testify. What information can you provide the jury concerning the allegation?

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Textbook Question

Consider the three pedigrees below, all involving a single human trait.

For each combination that you excluded, indicate the single individual in generation II (e.g., II-1, II-2) that was most instrumental in your decision to exclude it. If none were excluded, answer 'none apply.'

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Textbook Question

In goats, the development of the beard is due to a recessive gene. The following cross involving true-breeding goats was made and carried to the F₂ generation:

Offer an explanation for the inheritance and expression of this trait, diagramming the cross. Propose one or more crosses to test your hypothesis.

Textbook Question

Consider the three pedigrees below, all involving a single human trait.

Given your conclusions in part (a), indicate the genotype of the following individuals: II-1, II-6, II-9 If more than one possibility applies, list all possibilities. Use the symbols A and a for the genotypes.

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Textbook Question

Contrast penetrance and expressivity as the terms relate to phenotypic expression.