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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 20b
Chapter 3, Problem 20b

For each pedigree shown,
Four pedigrees illustrating inheritance patterns, showing individuals with filled and unfilled symbols for genetic traits.
Determine which other pattern(s) of transmission is/are possible. For each possible mode of transmission, specify the genotypes necessary for transmission to occur.

Verified step by step guidance
1
Examine the pedigree carefully to identify the pattern of inheritance. Look for clues such as whether the trait appears in every generation (dominant) or skips generations (recessive), and whether it affects males and females equally (autosomal) or disproportionately affects one sex (sex-linked).
Consider autosomal dominant inheritance: If the trait is dominant, individuals with the trait must have at least one dominant allele. Determine the genotypes of affected individuals (e.g., heterozygous Aa or homozygous AA) and unaffected individuals (e.g., homozygous recessive aa).
Consider autosomal recessive inheritance: If the trait is recessive, affected individuals must have two recessive alleles (aa). Unaffected individuals could be carriers (Aa) or homozygous dominant (AA). Check if the pattern fits this mode of inheritance.
Consider X-linked inheritance: If the trait is X-linked, analyze whether males (XY) and females (XX) are affected differently. For X-linked recessive traits, affected males must inherit the recessive allele from their mother, while affected females must inherit two recessive alleles. For X-linked dominant traits, affected males pass the trait to all daughters but not sons.
Summarize the possible modes of transmission and specify the genotypes required for each mode. For example, autosomal dominant requires Aa or AA for affected individuals, autosomal recessive requires aa, and X-linked inheritance requires specific combinations of alleles on the X chromosome.

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Key Concepts

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

Pedigree Analysis

Pedigree analysis is a diagrammatic method used to trace the inheritance of traits through generations in a family. It helps identify patterns of inheritance, such as autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive traits. By analyzing the pedigree, one can determine the likelihood of certain genotypes appearing in offspring based on the genotypes of the parents.
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Pedigree Flowchart

Modes of Inheritance

Modes of inheritance refer to the patterns through which genetic traits are passed from parents to offspring. The primary modes include autosomal dominant, where only one copy of a mutated gene is sufficient for expression, and autosomal recessive, where two copies are needed. Understanding these modes is crucial for predicting the genotypes of individuals in a pedigree and determining the likelihood of trait transmission.
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Genotype Specification

Genotype specification involves identifying the specific alleles present in an individual that contribute to a particular trait. In the context of pedigrees, it is essential to determine the genotypes of individuals to understand how traits are inherited. This includes recognizing homozygous and heterozygous conditions, which influence the expression of dominant and recessive traits in offspring.
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Related Practice
Textbook Question

Four eye-color mutants in Drosophila—apricot, brown, carnation, and purple—are inherited as recessive traits. Red is the dominant wild-type color of fruit-fly eyes. Eight crosses (A through H) are made between parents from pure-breeding lines.

Which of these eye-color mutants are X-linked recessive and which are autosomal recessive? Explain how you distinguish X-linked from autosomal heredity.

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Textbook Question

Four eye-color mutants in Drosophila—apricot, brown, carnation, and purple—are inherited as recessive traits. Red is the dominant wild-type color of fruit-fly eyes. Eight crosses (A through H) are made between parents from pure-breeding lines.

Predict F2 phenotype ratios of crosses A, B, D, and G.

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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. 

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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

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.

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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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