Textbook Problem

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Suppose you identify a new gene in mice. One of its alleles specifies white fur, another specifies brown. You want to see if these alleles are inherited in a Mendelian pattern, or with incomplete dominance. What crosses would give you the answer?

Summary Introduction

To explain: The crosses that would provide answer to check if the alleles for phenotype for white fur and brown fur are inherited based on Mendelian pattern of inheritance or non-Mendelian pattern of inheritance.

Concept introduction: Mendelian pattern of inheritance is where the ratio of the phenotypes in the case of monohybrid cross is 3:1 and that of dihybrid cross is 9:3:3:1. Any phenotypic ratio that deviates from the Mendelian pattern of inheritance falls under non-Mendelian inheritance category. Incomplete dominance is a type of non-Mendelian inheritance where the heterozygous phenotype is the intermediate of the homozygous dominant and homozygous recessive phenotypes.

Explanation of Solution

The alphabet for the alleles is assigned based on the dominant phenotype if they follow Mendelian pattern of inheritance.

For example:

• If the two phenotypes are brown and white and brown is dominant, then the alleles will be BB-brown and bb-white.
• If the two phenotypes are brown and white and white is dominant, then the alleles will be WW-white and ww-brown.

In case the alleles follow non-Mendelian pattern of inheritance, the alphabet is randomly assigned by the geneticists.

A true breeding white furred strain mouse and true breeding brown furred strain mouse are chosen as true breeding ones that always give heterozygous, and the phenotype of the heterozygous is the dominant allele. The F₁ generation is heterozygous. Also, the genes must not be linked as crossing over cannot occur to mix alleles. Assuming that the gene is present in only one locus, a monohybrid cross is performed between a true breeding white furred strain mouse and true breeding brown furred strain mouse.

The following are the possible outcomes:

Outcome 1:

The F₁ generation is brown, and the phenotypic ratio for F₂ generation is 3 Brown: 1 White...