In mice, a short-tailed mutant was discovered. When it was crossed to a normal long-tailed mouse, 4 offspring were short-tailed and 3 were long-tailed. Two short-tailed mice from the F1 generation were selected and crossed. They produced 6 short-tailed and 3 long-tailed mice. These genetic experiments were repeated three times with approximately the same results. What genetic ratios are illustrated? Hypothesize the mode of inheritance and diagram the crosses.

Verified step by step guidance

1. Identify the phenotypes and their ratios in the offspring from the initial cross between a short-tailed mutant and a normal long-tailed mouse. The ratio is approximately 1:1 (4 short-tailed: 3 long-tailed).
2. Hypothesize that the short tail trait is dominant over the long tail trait. Let 'S' represent the dominant short tail allele and 's' represent the recessive long tail allele.
3. Assume the genotype of the short-tailed mutant is heterozygous (Ss) and the normal long-tailed mouse is homozygous recessive (ss). Perform a Punnett square to confirm the 1:1 ratio in the F1 generation.
4. Select two short-tailed mice from the F1 generation (Ss) and cross them. Use a Punnett square to predict the genotypic and phenotypic ratios in the F2 generation. Expect a 3:1 phenotypic ratio (3 short-tailed: 1 long-tailed).
5. Diagram the crosses: First cross (Ss x ss) results in Ss and ss offspring. Second cross (Ss x Ss) results in SS, Ss, and ss offspring, confirming the observed 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 traits. In this case, the short-tailed trait appears to be dominant over the long-tailed trait, as evidenced by the offspring ratios observed in the crosses. Understanding these principles is crucial for predicting the inheritance patterns of traits in subsequent generations.

Phenotypic Ratios

Phenotypic ratios represent the relative frequencies of different phenotypes in the offspring resulting from a genetic cross. In the given scenario, the observed ratios of 4 short-tailed to 3 long-tailed mice in the first cross, and 6 short-tailed to 3 long-tailed in the second, suggest a consistent ratio of approximately 2:1 for the dominant trait. Analyzing these ratios helps in determining the mode of inheritance.

Punnett Square

A Punnett square is a diagram used to predict the genotypes and phenotypes of offspring from a genetic cross. By mapping the alleles of the parents, it visually represents the possible combinations and their probabilities. In this case, constructing Punnett squares for the crosses can help illustrate the inheritance patterns and confirm the hypothesized dominance of the short-tailed trait.