Ch. 4 - Modification of Mendelian Ratios

Klug - Essentials of Genetics 10th Edition

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Klug 10th Edition

Ch. 4 - Modification of Mendelian Ratios

Problem 4

Chapter 4, Problem 4

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 shorthorn cattle, coat color may be red, white, or roan. Roan is an intermediate phenotype expressed as a mixture of red and white hairs. The following data were obtained from various crosses:

How is coat color inherited? What are the genotypes of parents and offspring for each cross?

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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

Three gene pairs located on separate autosomes determine flower color and shape as well as plant height. The first pair exhibits incomplete dominance, where the color can be red, pink (the heterozygote), or white. The second pair leads to personate (dominant) or peloric (recessive) flower shape, while the third gene pair produces either the dominant tall trait or the recessive dwarf trait. Homozygous plants that are red, personate, and tall are crossed to those that are white, peloric, and dwarf. Determine the F₁ genotype(s) and phenotype(s). If the F₁ plants are interbred, what proportion of the offspring will exhibit the same phenotype as the F₁ plants?

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Textbook Question

Flower color may be red, white, or pink, and flower shape may be personate or peloric. For the following crosses, determine the P₁ and F₁ genotypes:

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