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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 21
Chapter 3, Problem 21

Consider the following pedigree.
Pedigree chart showing four generations with affected males and females marked by filled blue squares and circles.
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.

Verified step by step guidance
1
Step 1: Analyze the pattern of affected individuals across generations. Notice that both males and females are affected, and the trait appears in every generation, suggesting it is likely a dominant trait.
Step 2: Check if the trait skips generations. Since affected individuals are present in each generation, this supports the idea of a dominant mode of inheritance rather than recessive.
Step 3: Consider the genotypes of the parents in generation I. Since individual I-2 is affected and I-1 is unaffected, and they have both affected and unaffected children, I-2 is likely heterozygous (A/a) and I-1 is homozygous recessive (a/a).
Step 4: Assign genotypes to individuals in generation II based on their parents' genotypes and their affected status. For example, affected individuals are likely A/a, and unaffected individuals are a/a.
Step 5: Continue this logic for generations III and IV, using the inheritance pattern and the genotypes of parents to predict the most probable genotype of each individual, remembering that affected individuals must have at least one dominant allele (A).

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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 dominant, recessive, autosomal, or sex-linked inheritance. Understanding how traits appear and skip generations is key to predicting genotypes.
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Pedigree Flowchart

Modes of Inheritance

Modes of inheritance describe how genetic traits are transmitted from parents to offspring. Common modes include autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive. Recognizing patterns such as affected individuals in every generation or skipping generations helps determine the mode.
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Organelle Inheritance

Genotype Prediction Using Alleles

Genotype prediction involves determining the genetic makeup (e.g., AA, Aa, or aa) of individuals based on their phenotype and family history. Using dominant (A) and recessive (a) alleles, one can infer carriers and affected individuals by analyzing who expresses the trait and how it segregates in the pedigree.
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Related Practice
Textbook Question

The following are F₂ results of two of Mendel's monohybrid crosses.

For each cross, state a null hypothesis to be tested using x² analysis. Calculate the x² value and determine the p value for both. Interpret the p-values. Can the deviation in each case be attributed to chance or not? Which of the two crosses shows a greater amount of deviation?

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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

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

1084
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Textbook Question

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

1091
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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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