Ch. 4 - Extensions of Mendelian Genetics

Klug - Concepts of Genetics 12th Edition

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Klug 12th Edition

Ch. 4 - Extensions of Mendelian Genetics

Problem 7

Chapter 4, Problem 7

With regard to the ABO blood types in humans, determine the genotype of the male parent and female parent shown here:
Male parent: Blood type B; mother type O
Female parent: Blood type A; father type B
Predict the blood types of the offspring that this couple may have and the expected proportion of each.

Verified step by step guidance

Step 1: Determine the possible genotypes of the male parent. Since the male has blood type B and his mother has blood type O, the male must have inherited an O allele from his mother. Therefore, the male's genotype is heterozygous B\/O (\( I^B I^O \)).

Step 2: Determine the possible genotypes of the female parent. The female has blood type A and her father has blood type B. Since the father is type B, he could have passed either a B or an O allele. The female's genotype could be either A\/A (\( I^A I^A \)) or A\/O (\( I^A I^O \)). Both are possible, so consider both cases for offspring prediction.

Step 3: Set up Punnett squares for each possible female genotype crossed with the male genotype B\/O (\( I^B I^O \)). For the female genotype A\/A (\( I^A I^A \)), cross \( I^A I^A \) with \( I^B I^O \). For the female genotype A\/O (\( I^A I^O \)), cross \( I^A I^O \) with \( I^B I^O \).

Step 4: From each Punnett square, list all possible genotypes of the offspring and determine their corresponding blood types: A (\( I^A I^A \) or \( I^A I^O \)), B (\( I^B I^B \) or \( I^B I^O \)), AB (\( I^A I^B \)), and O (\( I^O I^O \)).

Step 5: Calculate the expected proportion of each blood type among the offspring by counting the frequency of each genotype in the Punnett square and converting it to a percentage or fraction.

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Key Concepts

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

ABO Blood Group System

The ABO blood group system classifies human blood into four types (A, B, AB, O) based on the presence or absence of antigens on red blood cells. The A and B alleles are codominant, while O is recessive. Understanding this system is essential to determine possible genotypes and phenotypes in offspring.

Genotype Determination from Phenotype and Parental Information

Phenotypes (observable traits) like blood type can correspond to multiple genotypes. Using information about the parents’ blood types and their parents’ blood types helps infer the parents’ genotypes by considering dominant and recessive allele inheritance patterns.

Punnett Square and Probability of Offspring Genotypes

A Punnett square is a tool used to predict the genotypes and phenotypes of offspring from parental genotypes. It helps calculate the expected proportions of each blood type in the children by combining alleles from each parent according to Mendelian inheritance.

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Textbook Question

In foxes, two alleles of a single gene, P and p, may result in lethality (PP), platinum coat (Pp), or silver coat (pp). What ratio is obtained when platinum foxes are interbred? Is the P allele behaving dominantly or recessively in causing (a) lethality; (b) platinum coat color?

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Textbook Question

In mice, a short-tailed mutant was discovered. When it was crossed to a normal long-tailed mouse, 4 offspring were short-tailed and 3 were long-tailed. Two short-tailed mice from the F1 generation were selected and crossed. They produced 6 short-tailed and 3 long-tailed mice. These genetic experiments were repeated three times with approximately the same results. What genetic ratios are illustrated? Hypothesize the mode of inheritance and diagram the crosses.

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Textbook Question

List all possible genotypes for the A, B, AB, and O phenotypes. Is the mode of inheritance of the ABO blood types representative of dominance, recessiveness, or codominance?

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Textbook Question

In a disputed parentage case, the child is blood type O, while the mother is blood type A. What blood type would exclude a male from being the father? Would the other blood types prove that a particular male was the father?

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Textbook Question

The A and B antigens in humans may be found in water-soluble form in secretions, including saliva, of some individuals (Se/Se and Se/se) but not in others (se/se). The population thus contains 'secretors' and 'nonsecretors.'

Determine the proportion of various phenotypes (blood type and ability to secrete) in matings between individuals that are blood type AB and type O, both of whom are Se/se.

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Textbook Question

How will the results of such matings change if both parents are heterozygous for the gene controlling the synthesis of the H substance (Hh)?

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