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: 4/8 albino: 1/8 cream

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. One gene determines pigment production (e.g., A for pigment, a for no pigment), and the other gene determines pigment color (e.g., B for black, b for cream). Albino rats (aa) lack pigment regardless of the B gene, while black (A-B-) and cream (A-bb) rats depend on the presence of pigment (A-).
2. Analyze the offspring ratios: The offspring ratio is 3/8 black, 4/8 albino, and 1/8 cream. Convert these fractions into proportions to understand the genetic contributions. This suggests a 3:4:1 phenotypic ratio, which can be linked to specific genotypic combinations under the epistatic model.
3. Determine the parental genotypes: To produce the observed offspring ratios, the parents must be heterozygous for both genes. This means their genotypes are likely AaBb x AaBb. This allows for all possible combinations of alleles in the offspring, leading to the observed phenotypic ratios.
4. Predict the offspring genotypes: Use a Punnett square to cross AaBb x AaBb. This will result in a 16-square grid showing all possible combinations of alleles. The genotypes will include AABB, AABb, AaBB, AaBb (black), aaBB, aaBb, aabb (albino), and AAbb, Aabb (cream).
5. Link genotypes to phenotypes: Assign phenotypes to each genotype based on the inheritance pattern. For example, A-B- results in black, aa-- results in albino, and A-bb results in cream. Verify that the phenotypic ratios (3/8 black, 4/8 albino, 1/8 cream) match the observed offspring ratios.

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 inheritance of coat color in rats can be analyzed using Mendel's laws, particularly the law of segregation, which states that alleles segregate independently during gamete formation.

Genotype and Phenotype

The genotype is the genetic makeup of an organism, represented by the alleles it possesses, while the phenotype is the observable physical or biochemical characteristics resulting from the genotype. In the case of coat color in rats, understanding the relationship between the genotypes of the parents and the resulting phenotypes of the offspring is crucial for predicting inheritance patterns.

Punnett Square

A Punnett square is a diagram used to predict the genotypes of offspring from a cross between two parents. By mapping out the possible allele combinations from each parent, it helps visualize the probability of different phenotypes appearing in the offspring. This tool is essential for analyzing the inheritance ratios observed in the given offspring ratios of black, albino, and cream rats.