Ch. 14 - Mendel and the Gene Idea

Campbell - Campbell Biology 11th Edition

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Urry 11th Edition

Ch. 14 - Mendel and the Gene Idea

Problem 2

Chapter 14, Problem 2

A man with type A blood marries a woman with type B blood. Their child has type O blood. What are the genotypes of these three individuals? What genotypes, and in what frequencies, would you expect in future offspring from this marriage?

Verified step by step guidance

Step 1: Identify the blood types and their corresponding genotypes. Type A blood can be AA or AO, type B blood can be BB or BO, and type O blood is always OO.

Step 2: Determine the parents' genotypes based on the child's blood type. Since the child has type O blood (OO), each parent must have contributed an O allele. Therefore, the man's genotype must be AO and the woman's genotype must be BO.

Step 3: Use a Punnett square to predict the genotypes of future offspring. The Punnett square for this cross would look like this: | | A | O | |---|---|---| | B | AB | BO | | O | AO | OO |

Step 4: Determine the frequencies of the genotypes. According to the Punnett square, there is a 25% chance for each genotype (AB, BO, AO, OO) in future offspring.

Step 5: Translate the genotypes into blood types. The possible blood types for future offspring are A (AO), B (BO), AB (AB), and O (OO), each with a 25% chance.

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Key Concepts

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

Blood Type Genetics

Blood types are determined by the ABO gene, which has three alleles: A, B, and O. A and B are co-dominant, meaning that if both are present, both traits are expressed, while O is recessive. Therefore, individuals with type A blood can have genotypes AA or AO, and those with type B can have BB or BO. Type O blood results from the genotype OO.

Punnett Square

A Punnett square is a tool used in genetics to predict the genotypes of offspring from parental genotypes. By arranging the alleles of each parent along the axes of a grid, one can visualize the possible combinations of alleles in the offspring. This method helps in determining the probabilities of each genotype occurring in future generations.

Mendelian Inheritance

Mendelian inheritance refers to the patterns of inheritance first described by Gregor Mendel, which include the principles of segregation and independent assortment. These principles explain how alleles segregate during gamete formation and how traits are inherited independently of one another. Understanding these principles is crucial for predicting the genetic outcomes of offspring in a given cross.

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Textbook Question

Two pea plants heterozygous for the characters of pod color and pod shape are crossed. Draw a Punnett square to determine the phenotypic ratios of the offspring.

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Textbook Question

A man has six fingers on each hand and six toes on each foot. His wife and their daughter have the normal number of digits. Remember that extra digits is a dominant trait. What fraction of this couple's children would be expected to have extra digits?

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Textbook Question

A pea plant heterozygous for inflated pods (Ii) is crossed with a plant homozygous for constricted pods (ii). Draw a Punnett square for this cross to predict genotypic and phenotypic ratios. Assume that pollen comes from the ii plant.

Flower position, stem length, and seed shape are three characters that Mendel studied. Each is controlled by an independently assorting gene and has dominant and recessive expression as indicated in Table 14.1.

If a plant that is heterozygous for all three characters is allowed to self-fertilize, what proportion of the offspring would you expect to be each of the following? (Note: Use the rules of probability instead of a huge Punnett square.)

a. Homozygous for the three dominant traits

b. Homozygous for the three recessive traits

c. Heterozygous for all three characters

d. Homozygous for axial and tall, heterozygous for seed shape

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