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Ch. 3 - Mendelian Genetics
Klug - Concepts of Genetics 12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
All textbooksKlug 12th EditionCh. 3 - Mendelian GeneticsProblem 22a
Chapter 3, Problem 22a

Draw all possible conclusions concerning the mode of inheritance of the trait portrayed in the following limited pedigree.
Pedigree chart showing affected and unaffected family members across two generations with a trait highlighted in blue.

Verified step by step guidance
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Step 1: Identify the affected and unaffected individuals in the pedigree. Squares represent males, circles represent females, and shaded shapes indicate individuals affected by the trait.
Step 2: Observe the pattern of affected individuals across generations. Note that the father (square) in the first generation is affected, and among the children, one son and one daughter are affected, while the other two children are unaffected.
Step 3: Consider whether the trait could be autosomal or sex-linked. Since both males and females are affected, and the trait appears in every generation, this suggests the trait might be autosomal dominant.
Step 4: Check if the trait could be recessive. If it were recessive, unaffected parents would typically have affected offspring only if both parents are carriers. Here, the affected father has unaffected children, which is consistent with dominant inheritance where the affected parent can pass the trait to some children but not all.
Step 5: Conclude that the most likely mode of inheritance is autosomal dominant, as the trait appears in every generation and affects both sexes equally.

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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 tool used to study the inheritance patterns of traits through generations in a family. It uses standardized symbols to represent individuals and their traits, helping to identify whether a trait is dominant, recessive, autosomal, or sex-linked.
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Pedigree Flowchart

Modes of Inheritance

Modes of inheritance describe how traits are passed from parents to offspring, including autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive patterns. Recognizing these patterns in pedigrees helps determine the genetic basis of a trait.
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Organelle Inheritance

Interpretation of Affected and Unaffected Individuals

In pedigrees, affected individuals are typically shaded, while unaffected are unshaded. Analyzing the distribution of affected individuals across sexes and generations allows inference about dominance, recessiveness, and linkage, guiding conclusions about the trait's inheritance.
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Autosomal Pedigrees
Related Practice
Textbook Question

In assessing data that fell into two phenotypic classes, a geneticist observed values of 250:150. She decided to perform a χ\chi² analysis by using the following two different null hypotheses:

(a) the data fit a 3:1 ratio, and

(b) the data fit a 1:1 ratio.

Calculate the χ\chi ² values for each hypothesis. What can be concluded about each hypothesis?

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Textbook Question

The basis for rejecting any null hypothesis is arbitrary. The researcher can set more or less stringent standards by deciding to raise or lower the p value used to reject or not reject the hypothesis. In the case of the chi-square analysis of genetic crosses, would the use of a standard of p = 0.10 be more or less stringent about not rejecting the null hypothesis? Explain.

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Textbook Question

Consider the following pedigree.

Predict the mode of inheritance of the trait of interest and the most probable genotype of each individual. Assume that the alleles A and a control the expression.

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Textbook Question

Draw all possible conclusions concerning the mode of inheritance of the trait portrayed in the following limited pedigree.

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Textbook Question

Draw all possible conclusions concerning the mode of inheritance of the trait portrayed in the following limited pedigree.

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Textbook Question

Draw all possible conclusions concerning the mode of inheritance of the trait portrayed in the following limited pedigree.


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