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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 37c
Chapter 4, Problem 37c

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.

Verified step by step guidance
1
Understand the concept of epistasis: Epistasis occurs when the expression of one gene is affected by another gene. This interaction can modify the expected Mendelian ratios in genetic crosses.
Example 1: Recessive epistasis. In this case, the presence of two recessive alleles at one gene locus masks the expression of alleles at another locus. For instance, in Labrador retrievers, coat color is determined by two genes: one for pigment production (B/b) and another for pigment deposition (E/e). The F₂ ratio is modified to 9:3:4 instead of the typical 9:3:3:1.
Example 2: Dominant epistasis. Here, a dominant allele at one locus masks the expression of alleles at another locus. For example, in summer squash, the dominant allele (W) prevents pigment production regardless of the alleles at the second locus (Y/y). The F₂ ratio is modified to 12:3:1.
Describe how gene interaction results in modified ratios: In both examples, the interaction between the two genes alters the phenotypic expression of traits. This happens because one gene either blocks or overrides the effect of another gene, leading to fewer phenotypic categories than expected in a typical dihybrid cross.
To solve problems involving epistasis, construct a Punnett square for the dihybrid cross and apply the rules of gene interaction to determine the phenotypic ratios. Use the modified ratios (e.g., 9:3:4 or 12:3:1) to interpret the results.

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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 modified phenotypic ratios in offspring, particularly in dihybrid crosses. For example, in a classic case, one gene may mask the effect of another, altering the expected Mendelian ratios.
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Epistatic Genes

Dihybrid Cross

A dihybrid cross involves two traits, each controlled by different genes, typically represented by two pairs of alleles. The expected phenotypic ratio in a typical dihybrid cross without epistasis is 9:3:3:1. However, when epistatic interactions occur, this ratio can change, reflecting the influence of one gene on the expression of another.
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Punnet Square

Modified F₂ Ratios

Modified F₂ ratios arise when epistatic interactions alter the expected outcomes of genetic crosses. For instance, in a case of recessive epistasis, the ratio may shift from 9:3:3:1 to 9:7, indicating that certain combinations of alleles prevent the expression of other traits. Understanding these modifications is crucial for predicting phenotypic outcomes in genetic studies.
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Related Practice
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.

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

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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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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.

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

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