Four eye-color mutants in Drosophila—apricot, brown, carnation, and purple—are inherited as recessive traits. Red is the dominant wild-type color of fruit-fly eyes. Eight crosses (A through H) are made between parents from pure-breeding lines.

Predict F₂ phenotype ratios of crosses A, B, D, and G. <>

Verified step by step guidance

1. <Identify the genetic basis of each eye-color mutation: Determine which gene is affected by each mutation (apricot, brown, carnation, purple) and how it interacts with the wild-type allele.>
2. <Understand the inheritance pattern: Since all mutations are recessive, the wild-type red eye color is dominant. This means that a fly must have two copies of the mutant allele to express the mutant phenotype.>
3. <Analyze the F1 generation: For each cross (A, B, D, G), determine the genotype of the F1 generation. Since the parents are from pure-breeding lines, the F1 generation will be heterozygous for the trait.>
4. <Predict the F2 generation: Use a Punnett square to determine the possible genotypes and phenotypes of the F2 generation. Since the F1 generation is heterozygous, the F2 generation will show a 3:1 phenotypic ratio of dominant to recessive traits.>
5. <Summarize the expected F2 phenotype ratios: For each cross, state the expected ratio of red-eyed (wild-type) to mutant-eyed flies in the F2 generation, based on the 3:1 ratio typical of monohybrid crosses involving recessive traits.>

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 context, the eye color traits in Drosophila demonstrate how alleles interact, with red being the dominant trait and the mutants (apricot, brown, carnation, and purple) being recessive. Understanding these principles is essential for predicting the phenotypic ratios in offspring from specific crosses.

Phenotypic Ratios

Phenotypic ratios represent the relative frequencies of different phenotypes in the offspring resulting from genetic crosses. In this case, the F₂ generation's phenotypic ratios can be predicted based on the genotypes of the parents and the inheritance patterns of the eye color traits. Analyzing these ratios helps in understanding the distribution of traits in the population.

Pure-Breeding Lines

Pure-breeding lines consist of organisms that consistently produce offspring with the same phenotype when self-fertilized or crossed with other individuals of the same line. In the context of the question, the use of pure-breeding lines for the eye color mutants allows for clear predictions of the F₂ generation's phenotypes, as these lines are homozygous for their respective traits, simplifying the genetic analysis.