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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 9b
Chapter 4, Problem 9b

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)?

Verified step by step guidance
1
Understand the genetic basis of the problem: The ability to secrete A and B antigens in bodily fluids is controlled by the 'Se' gene. Individuals with at least one dominant allele (Se/Se or Se/se) are secretors, while individuals with the homozygous recessive genotype (se/se) are nonsecretors. Additionally, the synthesis of the H substance, which is required for the expression of A and B antigens, is controlled by the 'H' gene. Individuals with at least one dominant allele (Hh or HH) can produce the H substance, while individuals with the homozygous recessive genotype (hh) cannot produce the H substance, making them functionally blood type O regardless of their ABO genotype.
Determine the genotypes of the parents: Both parents are heterozygous for the 'H' gene (Hh) and the 'Se' gene (Se/se). This means that each parent can pass on either the 'H' or 'h' allele for the H gene and either the 'Se' or 'se' allele for the Se gene to their offspring.
Set up a Punnett square for the 'H' gene: Since both parents are Hh, the possible genotypes for their offspring are HH, Hh, and hh. The probabilities are 1/4 for HH, 1/2 for Hh, and 1/4 for hh.
Set up a Punnett square for the 'Se' gene: Since both parents are Se/se, the possible genotypes for their offspring are Se/Se, Se/se, and se/se. The probabilities are 1/4 for Se/Se, 1/2 for Se/se, and 1/4 for se/se.
Combine the results of the two Punnett squares: To determine the phenotypes of the offspring, consider the combinations of the 'H' and 'Se' genotypes. For example, individuals with at least one 'H' allele and at least one 'Se' allele will be secretors, while individuals with the hh genotype will not produce the H substance and will not express A or B antigens regardless of their Se genotype. Calculate the probabilities for each phenotype by multiplying the probabilities of the corresponding genotypes from the two Punnett squares.

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Key Concepts

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

H Substance and Blood Group Antigens

The H substance is a precursor for the A and B antigens found on red blood cells. Individuals with the Hh genotype can produce this substance, which is necessary for the synthesis of A and B antigens. If a person lacks the H substance (hh), they cannot express A or B antigens, regardless of their genotype for the A and B alleles.
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Secretor Status

Secretor status refers to the ability of individuals to secrete blood group antigens into bodily fluids, such as saliva. This trait is determined by the Se gene, where individuals with at least one Se allele (Se/Se or Se/se) are classified as 'secretors,' while those with the se/se genotype are 'nonsecretors.' This status can influence the presence of antigens in secretions but does not affect blood type directly.
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Mendelian Inheritance

Mendelian inheritance describes how traits are passed from parents to offspring through alleles. In this scenario, both parents are heterozygous (Hh) for the H substance gene, leading to a Punnett square analysis that predicts the genotypic ratios of their offspring. The potential combinations (HH, Hh, Hh, hh) will determine the offspring's ability to produce the H substance and, consequently, their blood group antigen expression.
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Related Practice
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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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

In rabbits, a series of multiple alleles controls coat color in the following way: C is dominant to all other alleles and causes full color. The chinchilla phenotype is due to the cch allele, which is dominant to all alleles other than C. The ch allele, dominant only to (albino), results in the Himalayan coat color. Thus, the order of dominance is C > cch > ch > ca. For each of the following three cases, the phenotypes of the P1 generations of two crosses are shown, as well as the phenotype of one member of the F1 generation.

For each case, determine the genotypes of the P1 generation and the F1 offspring, and predict the results of making each indicated cross between F1 individuals.

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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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