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:
3/8 black: 3/8 cream: 2/8 albino

Verified step by step guidance

1. Understand the inheritance pattern: Based on the problem, coat color in rats is likely determined by two genes with epistatic interactions. Epistasis occurs when one gene masks or modifies the expression of another gene. For example, one gene may control pigment production (e.g., albino vs. pigmented), while another gene determines the specific pigment color (e.g., black vs. cream).
2. Analyze the offspring ratios: The offspring are in the ratio 3/8 black, 3/8 cream, and 2/8 albino. This suggests a dihybrid cross involving two genes. The 2/8 albino offspring indicate that one gene is epistatic and prevents pigment production when homozygous recessive (e.g., aa). The remaining 6/8 (3/8 black + 3/8 cream) offspring are pigmented, which suggests the second gene determines the specific coat color (e.g., black vs. cream).
3. Determine the genotypes of the parents: Since the offspring include all three phenotypes (black, cream, and albino) in a specific ratio, the parents are likely heterozygous for both genes. For example, their genotypes could be AaBb x AaBb, where 'A' controls pigment production (A = pigmented, a = albino) and 'B' controls coat color (B = black, b = cream).
4. Set up a Punnett square: To confirm the genotypes of the parents, construct a 4x4 Punnett square for the dihybrid cross AaBb x AaBb. This will show all possible combinations of alleles in the offspring and their corresponding phenotypes. For example, offspring with genotype A_B_ (A and B are dominant) will be black, A_bb will be cream, and aa__ (aa with any combination of B or b) will be albino.
5. Verify the phenotypic ratios: After completing the Punnett square, count the offspring phenotypes to ensure they match the observed ratios (3/8 black, 3/8 cream, 2/8 albino). This will confirm the genotypes of the parents and the inheritance pattern of coat color in rats.

Key Concepts

Mendelian Inheritance

Mendelian inheritance refers to the principles of heredity established by Gregor Mendel, which include the concepts of dominant and recessive alleles. In this context, the coat color in rats is likely determined by alleles where one color is dominant over others. Understanding how these alleles segregate and assort during gamete formation is crucial for predicting offspring phenotypes.

Genotype and Phenotype

The genotype is the genetic makeup of an organism, represented by the alleles it carries, while the phenotype is the observable physical or biochemical characteristics resulting from the genotype. In this question, identifying the genotypes of the parents based on the phenotypic ratios of the offspring is essential for understanding the inheritance pattern of coat color in rats.

Punnett Square

A Punnett square is a diagram used to predict the genetic outcomes of a cross between two organisms. It helps visualize the possible combinations of alleles from the parents and the resulting genotypes and phenotypes of the offspring. Utilizing a Punnett square can clarify how the observed ratios of black, cream, and albino offspring arise from specific parental genotypes.