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Ch. 3 - Cell Division and Chromosome Heredity
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 3 - Cell Division and Chromosome HeredityProblem 21
Chapter 3, Problem 21

Use the blank pedigrees provided to depict transmission of
(a) an X-linked recessive trait and
(b) an X-linked dominant trait, by filling in circles and squares to represent individuals with the trait of interest. Give genotypes for each person in each pedigree.
Carefully design each transmission pattern so that pedigree
(a) cannot be confused with autosomal recessive transmission and pedigree
(b) cannot be confused with autosomal dominant transmission. Identify the transmission events that eliminate the possibility of autosomal transmission for each pedigree.
Two blank pedigrees illustrating X-linked recessive (a) and X-linked dominant (b) trait inheritance patterns.

Verified step by step guidance
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Step 1: Understand the inheritance patterns of X-linked traits. X-linked recessive traits are typically expressed in males (XY) who inherit the affected X chromosome, while females (XX) are usually carriers unless they inherit two affected X chromosomes. X-linked dominant traits are expressed in both males and females, but females may have a higher likelihood of being affected due to having two X chromosomes.
Step 2: For pedigree (a) (X-linked recessive trait), depict a male with the trait (affected X chromosome) and ensure that his daughters are carriers (one affected X chromosome and one normal X chromosome). His sons should not inherit the trait since they receive the Y chromosome from their father. This transmission pattern eliminates the possibility of autosomal recessive inheritance because autosomal traits do not depend on sex chromosomes.
Step 3: For pedigree (b) (X-linked dominant trait), depict an affected father passing the trait to all his daughters (since they inherit his affected X chromosome) but not to his sons (since they inherit his Y chromosome). This transmission pattern eliminates the possibility of autosomal dominant inheritance because autosomal traits would affect both sons and daughters equally.
Step 4: Assign genotypes to each individual in both pedigrees. For pedigree (a), affected males should have the genotype X^aY, carrier females should have the genotype X^AX^a, and unaffected individuals should have genotypes X^AY or X^AX^A. For pedigree (b), affected individuals should have the genotype X^AX^A or X^AY, and unaffected individuals should have genotypes X^AX^A or X^AY.
Step 5: Carefully label the transmission events in each pedigree that eliminate the possibility of autosomal inheritance. For pedigree (a), highlight the absence of male-to-male transmission and the carrier status of females. For pedigree (b), emphasize the father-to-daughter transmission and the absence of father-to-son transmission.

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Key Concepts

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

X-linked Inheritance

X-linked inheritance refers to the pattern of genetic transmission where genes are located on the X chromosome. In X-linked recessive traits, males (XY) are more likely to express the trait since they have only one X chromosome, while females (XX) can be carriers if they have one affected X. In contrast, X-linked dominant traits can affect both males and females, but females may show milder symptoms due to the presence of a second, normal X chromosome.
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X-Inactivation

Pedigree Analysis

Pedigree analysis is a method used to trace the inheritance patterns of traits through generations in a family tree. Squares represent males and circles represent females, with filled shapes indicating individuals expressing the trait. By analyzing the connections and affected individuals, one can determine whether a trait is autosomal or X-linked, as well as dominant or recessive, based on the patterns of inheritance observed.
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Pedigree Flowchart

Distinguishing Autosomal from X-linked Traits

To distinguish between autosomal and X-linked traits, one must observe the inheritance patterns. For X-linked recessive traits, affected males cannot pass the trait to their sons but can pass it to daughters, who may become carriers. In contrast, X-linked dominant traits can be passed from an affected parent to both sons and daughters. Autosomal traits, however, show a more uniform distribution across genders, making it crucial to identify these patterns in pedigree analysis.
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X-Inactivation
Related Practice
Textbook Question

In a species of fish, a black spot on the dorsal fin is observed in males and females. A fish breeder carries out a pair of reciprocal crosses and observes the following results.

  

Why does this evidence support the hypothesis that a black spot is sex linked?

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Textbook Question

The following figure illustrates reciprocal crosses involving chickens with sex-linked dominant barred mutation. For Cross A and for Cross B, cross the F₁ roosters and hens and predict the feather patterns of roosters and hens in the F2.

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Textbook Question

In fruit flies, yellow body (y) is recessive to gray body , and the trait of body color is inherited on the X chromosome. Vestigial wing (v) is recessive to full-sized wing (v⁺), and the trait has autosomal inheritance. A cross of a male with yellow body and full wings to a female with gray body and full wings is made. Based on an analysis of the progeny of the cross shown below, determine the genotypes of parental and progeny flies.

[Table below appears at this point containing crosses and results]

Textbook Question

For each pedigree shown,

Identify which simple pattern of hereditary transmission (autosomal dominant, autosomal recessive, X-linked dominant, or X-linked recessive) is most likely to have occurred. Give genotypes for individuals involved in transmitting the trait. 

Textbook Question

For each pedigree shown,

Identify which pattern(s) of transmission is/are impossible. Specify why transmission is impossible.

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Textbook Question

For each pedigree shown,

Determine which other pattern(s) of transmission is/are possible. For each possible mode of transmission, specify the genotypes necessary for transmission to occur.

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