Ch. 4 - Extensions of Mendelian Genetics

Klug - Concepts of Genetics 12th Edition

Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook

Klug 12th Edition

Ch. 4 - Extensions of Mendelian Genetics

Problem 8

Chapter 4, Problem 8

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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Understand the basics of blood type inheritance: Blood type is determined by the ABO gene, which has three alleles: A, B, and O. The A and B alleles are dominant, while the O allele is recessive.

Determine the possible genotypes for the mother: Since the mother is blood type A, her genotype could be either AA or AO.

Determine the child's genotype: The child is blood type O, which means their genotype must be OO, receiving one O allele from each parent.

Identify the possible genotypes for the father: To have a child with blood type O, the father must contribute an O allele. Therefore, the father could be blood type O (genotype OO), blood type A (genotype AO), or blood type B (genotype BO).

Determine which blood type would exclude a male from being the father: A male with blood type AB (genotype AB) cannot be the father, as he cannot contribute an O allele to the child.

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Key Concepts

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

Blood Type Inheritance

Blood type is determined by the ABO gene, which has three alleles: A, B, and O. A person inherits one allele from each parent, resulting in four possible blood types: A, B, AB, and O. In this case, the mother with blood type A can have either AA or AO genotype, while the child with blood type O must have inherited an O allele from both parents.

Paternity Testing and Blood Type Compatibility

Paternity can be inferred through blood type compatibility. If a child has blood type O, both parents must contribute an O allele. Therefore, a male with blood type AB (which has no O allele) can be excluded as the father. Other blood types, such as A or B, may or may not confirm paternity, depending on the specific alleles inherited.

Exclusion vs. Inclusion in Paternity Cases

In paternity testing, exclusion means that a potential father cannot be the biological parent based on blood type, while inclusion suggests that he could be. For example, a male with blood type O or A (AO genotype) could potentially be the father, while a male with blood type AB is definitively excluded. This distinction is crucial in legal and familial contexts.

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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.'

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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Textbook Question

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.

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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

In chickens, a condition referred to as 'creeper' exists whereby the bird has very short legs and wings and appears to be creeping when it walks. If creepers are bred to normal chickens, one-half of the offspring are normal and one-half are creepers. Creepers never breed true. If bred together, they yield two-thirds creepers and one-third normal. Propose an explanation for the inheritance of this condition.

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Textbook Question

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

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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