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Ch. 4 - Gene Interaction
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 4 - Gene InteractionProblem 37b
Chapter 4, Problem 37b

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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1
Epistasis is a genetic principle where one gene's expression masks or modifies the expression of another gene at a different locus. This interaction alters the expected Mendelian ratios in offspring.
In a dihybrid cross, the typical Mendelian F₂ ratio is 9:3:3:1, which assumes independent assortment and no interaction between genes. However, epistasis modifies this ratio depending on the type of interaction.
To understand the modified F₂ ratio, identify the type of epistasis involved. Common types include recessive epistasis (9:3:4), dominant epistasis (12:3:1), and duplicate gene interaction (15:1), among others.
Determine the phenotypic categories and how the alleles at one locus influence the expression of alleles at the second locus. For example, in recessive epistasis, the homozygous recessive genotype at one locus masks the expression of the other gene.
Finally, use a Punnett square or branch diagram to calculate the expected phenotypic ratios based on the specific type of epistatic interaction. This will help confirm the modified F₂ ratio.

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Key Concepts

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

Epistasis

Epistasis refers to the interaction between genes where the expression of one gene is affected by one or more other genes. This can lead to modifications in phenotypic ratios, particularly in dihybrid crosses, where the expected Mendelian ratios may not occur due to the masking or altering effects of one gene over another.
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Dihybrid Cross

A dihybrid cross involves two traits, each controlled by different genes, typically represented by two pairs of alleles. In a standard dihybrid cross, the expected phenotypic ratio in the F₂ generation is 9:3:3:1, assuming independent assortment. However, epistatic interactions can alter this ratio, leading to different outcomes.
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Mendelian Inheritance

Mendelian inheritance is the set of principles derived from Gregor Mendel's experiments with pea plants, which describe how traits are passed from parents to offspring. These principles include the law of segregation and the law of independent assortment, which form the basis for predicting genetic ratios in offspring, although epistatic interactions can complicate these predictions.
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Related Practice
Textbook Question

Cross-1 shown in the following figure illustrates genetic complementation of flower-color mutants. The produced from this cross of two pure-breeding mutant parental plants are dihybrid (CcPp) and have wild-type flower color. If these F₁ are allowed to self-fertilize, what phenotypes are expected in the F₂ , and what are the expected ratios of the phenotypes?


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Textbook Question

The wild-type allele of a gene has an A–T base pair at a particular location in its sequence, and a mutant allele of the same gene has a G–C base pair at the same location. Otherwise, the sequences of the two alleles are identical. Does this information tell you anything about the dominance relationship of the alleles? Explain why or why not.

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Textbook Question

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

What is the expected F₂ ratio?

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Textbook Question

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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Textbook Question

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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Textbook Question

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?

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