Given the inheritance pattern of coat color in rats described in Problem 17, predict the genotype and phenotype of the parents who produced the following offspring:
9/16 gray: 3/16 yellow: 3/16 black: 1/16 cream

Verified step by step guidance

1. Identify the inheritance pattern described in Problem 17, which likely involves two genes with epistatic interactions affecting coat color in rats. Typically, such ratios suggest a dihybrid cross with epistasis.
2. Assign symbols to the genes involved. For example, let gene A control pigment production (A = pigment, a = no pigment) and gene B control pigment color (B = black, b = yellow). The cream phenotype might result from a double recessive or interaction between these genes.
3. Write down the expected phenotypic ratios for a dihybrid cross with epistasis. The given offspring ratio (9/16 gray, 3/16 yellow, 3/16 black, 1/16 cream) suggests a 9:3:3:1 ratio, typical of independent assortment without epistasis, but with different phenotypes assigned to each genotype combination.
4. Determine the genotypes corresponding to each phenotype based on the gene symbols. For example, gray might be A_B_, yellow A_bb, black aaB_, and cream aabb. This helps to map phenotypes to genotypes.
5. Use the offspring phenotypic ratio to infer the parental genotypes. Since the ratio matches a 9:3:3:1 ratio, the parents are likely heterozygous for both genes (AaBb x AaBb). Confirm this by setting up a Punnett square and verifying the offspring ratios.

Key Concepts

Mendelian Inheritance and Dihybrid Crosses

Mendelian inheritance explains how traits are passed from parents to offspring through dominant and recessive alleles. A dihybrid cross involves two genes, each with two alleles, producing a 9:3:3:1 phenotypic ratio in the F2 generation when both parents are heterozygous for both traits.

Epistasis and Coat Color Genetics

Epistasis occurs when one gene masks or modifies the expression of another gene. In coat color genetics, interactions between multiple genes can produce complex phenotypic ratios different from classic Mendelian ratios, such as the presence of cream or yellow colors influenced by gene interactions.

Genotype to Phenotype Prediction

Predicting genotype and phenotype involves using observed offspring ratios to infer parental genotypes. By comparing expected Mendelian ratios to observed data, one can deduce which alleles parents carry and how they combine to produce specific phenotypes in offspring.