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Ch. 4 - Extensions of Mendelian Genetics
Klug - Concepts of Genetics 12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
All textbooksKlug 12th EditionCh. 4 - Extensions of Mendelian GeneticsProblem 6
Chapter 4, Problem 6

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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1
Understand that the ABO blood group system is determined by the presence of antigens on the surface of red blood cells, which are controlled by the ABO gene.
Identify the alleles involved: A, B, and O. The A and B alleles are codominant, meaning both can be expressed simultaneously, while the O allele is recessive.
List the possible genotypes for each phenotype: A phenotype can be IAIA or IAi, B phenotype can be IBIB or IBi, AB phenotype can only be IAIB, and O phenotype can only be ii.
Recognize that the mode of inheritance for the ABO blood types is an example of codominance, as both A and B alleles can be expressed together in the AB phenotype.
Note that the O phenotype is an example of recessiveness, as it only appears when both alleles are the recessive i allele.

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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 main phenotypes: A, B, AB, and O, based on the presence or absence of antigens on the surface of red blood cells. The A and B alleles are responsible for the A and B antigens, while the O allele does not produce any antigens. Understanding this system is crucial for determining the possible genotypes associated with each phenotype.
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Genotypes and Phenotypes

A genotype refers to the genetic constitution of an individual, while a phenotype is the observable expression of that genotype. For the ABO blood types, the possible genotypes include AA, AO (for phenotype A), BB, BO (for phenotype B), AB (for phenotype AB), and OO (for phenotype O). Recognizing the relationship between genotypes and phenotypes is essential for listing all possible genotypes for the given blood types.
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Codominance

Codominance is a form of inheritance where both alleles in a heterozygous individual contribute equally and visibly to the phenotype. In the case of the ABO blood types, the A and B alleles are codominant, meaning that individuals with genotype AB express both A and B antigens. This concept is key to understanding the inheritance pattern of the ABO blood group system, distinguishing it from simple dominance and recessiveness.
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Related Practice
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
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

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 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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