Question

Students taking a genetics exam were expected to answer the following question by converting data to a “meaningful ratio” and then solving the problem. The instructor assumed that the final ratio would reflect two gene pairs, and most correct answers did. Here is the exam question:
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Convert the data to a meaningful ratio that allows you to explain the inheritance of color. Determine the number of genes involved and the genotypes that yield each phenotype.”
a.Solve the problem for two gene pairs. What is the final ratio?

Accepted Answer

Step 1: Identify the phenotypic classes and their observed numbers from the data provided. List each phenotype and the corresponding count of individuals exhibiting that phenotype. Step 2: Convert the observed numbers into a ratio by dividing each phenotype count by the greatest common divisor or by the smallest number in the dataset to simplify the ratio into whole numbers. This ratio should reflect the relative frequencies of each phenotype. Step 3: Recall that two gene pairs typically produce a phenotypic ratio based on independent assortment and dominance relationships. For two gene pairs, the expected phenotypic ratio often follows a 9:3:3:1 pattern if both genes assort independently and show simple dominance. Step 4: Compare the simplified observed ratio to the expected 9:3:3:1 ratio. Determine if the observed data fits this pattern or if it suggests a different interaction (such as epistasis or linkage). This comparison helps confirm the number of genes involved. Step 5: Assign genotypes to each phenotype class based on the two gene pairs. For example, the phenotype with the highest frequency (9 parts) corresponds to the double dominant or dominant/recessive combinations, while the other phenotypes correspond to heterozygous or homozygous recessive combinations. Write out the genotypes that produce each phenotype accordingly.

주요 개념

Mendelian Inheritance and Dihybrid Crosses

Phenotypic Ratios and Their Interpretation

Genotype-Phenotype Relationships