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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 30a
Chapter 4, Problem 30a

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

Which combination of conditions, if any, can be excluded? dominant and X-linked dominant and autosomal recessive and X-linked recessive and autosomal

Verified step by step guidance
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Step 1: Identify the pattern of affected individuals in each pedigree. Note the sex of affected individuals (squares for males, circles for females) and whether the trait appears in every generation or skips generations.
Step 2: For autosomal dominant traits, affected individuals usually appear in every generation and both males and females are equally likely to be affected. Check if this pattern fits any of the pedigrees.
Step 3: For X-linked dominant traits, affected males pass the trait to all daughters but no sons, and affected females can pass it to both sons and daughters. Look for affected females in every generation and affected males passing the trait to daughters.
Step 4: For autosomal recessive traits, the trait can skip generations, and affected individuals can have unaffected parents. Both males and females are equally affected. Check if the trait appears in siblings but not parents.
Step 5: For X-linked recessive traits, more males are affected than females, and affected males usually inherit the trait from carrier mothers. Affected males do not pass the trait to sons but can pass the allele to daughters who become carriers. Look for this pattern in the pedigrees.

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Key Concepts

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

Modes of Inheritance

Modes of inheritance describe how traits are passed from parents to offspring. Common types include autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive. Each mode has distinct patterns in pedigrees, such as affected individuals in every generation for dominant traits or skipping generations for recessive traits.
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Pedigree Analysis

Pedigree analysis involves studying family trees to track the inheritance of traits. Squares represent males, circles represent females, and shaded symbols indicate affected individuals. By examining affected and unaffected members across generations, one can infer the likely mode of inheritance.
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Pedigree Flowchart

X-linked vs Autosomal Traits

X-linked traits are associated with genes on the X chromosome and often show different patterns between males and females, such as males being more frequently affected in X-linked recessive traits. Autosomal traits are located on non-sex chromosomes and typically affect males and females equally.
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Related Practice
Textbook Question

While vermilion is X-linked in Drosophila and causes the eye color to be bright red, brown is an autosomal recessive mutation that causes the eye to be brown. Flies carrying both mutations lose all pigmentation and are white-eyed. Predict the F₁ and F₂ results of the following crosses:

white females x wild-type males

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Textbook Question

In a cross in Drosophila involving the X-linked recessive eye mutation white and the autosomally linked recessive eye mutation sepia (resulting in a dark eye), predict the F₁ and F₂ results of crossing true-breeding parents of the following phenotypes: Note that white is epistatic to the expression of sepia.

white females x sepia males

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Textbook Question

In a cross in Drosophila involving the X-linked recessive eye mutation white and the autosomally linked recessive eye mutation sepia (resulting in a dark eye), predict the F₁ and F₂ results of crossing true-breeding parents of the following phenotypes: Note that white is epistatic to the expression of sepia.

sepia females x white males

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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

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

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.

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