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Ch. 4 - Gene Interaction
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
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Tutti i libri di testoSanders 3rd EditionCh. 4 - Gene InteractionProblema 38b
Capitolo 4, Problema 38b

Draw a pedigree containing two parents and four children. Both of the parents have an AB blood type. The first child is type A, the second child is type AB, and the third child is type B.
The fourth child tests as having blood type O, which is not possible given the parental genotypes. Look at the Figure below and read the description of the molecular process that generates ABO blood group antigens. What other mutation could account for this observation?
Table showing blood types A, B, AB, O with clumping reactions to Anti-A and Anti-B and possible genotypes.

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Start by drawing a pedigree chart with two parents connected by a horizontal line, indicating mating, and four children connected below them with vertical lines.
Label both parents with the blood type AB. Since AB blood type means each parent has one A allele and one B allele, their genotype is I^A I^B.
Assign the blood types to the children as given: the first child is type A, the second is type AB, the third is type B, and the fourth is type O. Note that the first three children's blood types are consistent with the parents' genotypes, but the fourth child's type O is unexpected.
Recall that blood type O corresponds to the genotype I^O I^O, meaning the child must have inherited two O alleles. Since neither parent has an O allele, this is genetically impossible under normal inheritance.
Consider the molecular basis of ABO blood groups: the I^A and I^B alleles encode enzymes that modify the H antigen on red blood cells, while the I^O allele is a nonfunctional variant. A possible explanation for the fourth child's type O blood is a mutation in the FUT1 gene (which encodes the H antigen), leading to the Bombay phenotype, where the H antigen is not produced, masking the presence of A or B antigens and resulting in a type O blood phenotype despite the genotype.

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ABO Blood Group Inheritance

The ABO blood group system is determined by three alleles: A, B, and O. Each parent contributes one allele, and the combination determines the blood type. Parents with AB blood type have one A and one B allele, so their children can have A, B, or AB types, but not O, since O requires two O alleles.
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Percorso guidato
05:13
Organelle Inheritance

Molecular Basis of ABO Antigens

ABO blood types arise from specific glycosyltransferase enzymes encoded by the ABO gene, which modify the H antigen on red blood cells. The A and B alleles produce enzymes that add different sugar residues, while the O allele results from a nonfunctional enzyme, leaving the H antigen unmodified.
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07:11
Mapping with Markers

Mutations Affecting ABO Phenotype

Mutations in the ABO gene can alter enzyme function, leading to unexpected blood types. For example, a mutation causing a loss of function in one allele of an AB parent could produce a nonfunctional enzyme similar to O, explaining a child with type O blood despite parents having AB genotypes.
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Percorso guidato
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Mutations and Phenotypes
Pratica correlata
Domanda del libro di testo

Epistatic gene interaction results in a modification of the F₂ dihybrid ratio.

Give two examples of modified F₂ ratios produced by epistatic gene interactions and describe how gene interaction results in the ratios.

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Domanda del libro di testo

Draw a pedigree containing two parents and four children. Both of the parents have AB blood type. The first child is type A, the second child is type AB, and the third child is type B.

What is the name of the genetic phenomenon producing this observation?

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Domanda del libro di testo

Epistatic gene interaction results in a modification of the F₂ dihybrid ratio.

What genetic principle is the basis of this expected F₂ ratio?

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Domanda del libro di testo

Draw a pedigree containing two parents and four children. Both of the parents have AB blood type. The first child is type A, the second child is type AB, and the third child is type B.


Assign the genotypes to these five people.

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