A geneticist crosses a pure-breeding strain of peas producing yellow, wrinkled seeds with one that is pure-breeding for green, round seeds.
What is the expected phenotype distribution among the F₂ progeny?

Verified step by step guidance

1. Step 1: Identify the traits and their inheritance patterns. Yellow and green seed color are determined by one gene, and round and wrinkled seed shape are determined by another gene. Assume that yellow (Y) is dominant to green (y), and round (R) is dominant to wrinkled (r).
2. Step 2: Determine the genotype of the parental strains. The pure-breeding yellow, wrinkled strain will have the genotype YYrr, and the pure-breeding green, round strain will have the genotype yyRR.
3. Step 3: Perform a Punnett square for the F₁ generation. Cross YYrr with yyRR. The F₁ progeny will all have the genotype YyRr, which is heterozygous for both traits. Their phenotype will be yellow and round due to dominance.
4. Step 4: Perform a dihybrid cross for the F₂ generation. Cross two F₁ individuals (YyRr × YyRr). Use a 4x4 Punnett square to determine all possible combinations of alleles for the F₂ progeny. Each parent contributes one allele for each gene.
5. Step 5: Analyze the results of the dihybrid cross. The expected phenotype ratio among the F₂ progeny will follow Mendel's law of independent assortment, resulting in a 9:3:3:1 ratio: 9 yellow round, 3 yellow wrinkled, 3 green round, and 1 green wrinkled.

Key Concepts

Mendelian Genetics

Mendelian genetics is the study of how traits are inherited through generations, based on the principles established by Gregor Mendel. It involves understanding dominant and recessive alleles, where dominant traits mask the expression of recessive ones. In this case, yellow seeds (Y) are dominant over green seeds (y), and round seeds (R) are dominant over wrinkled seeds (r).

Punnett Square

A Punnett square is a diagram used to predict the genotypic and phenotypic outcomes of a genetic cross. By organizing the alleles from each parent, it allows for the visualization of potential combinations in the offspring. For the given cross, the Punnett square will help determine the expected ratios of yellow, green, round, and wrinkled seeds in the F₂ generation.

Phenotypic Ratio

The phenotypic ratio refers to the relative frequency of different phenotypes in the offspring resulting from a genetic cross. In this scenario, the expected phenotypic ratio among the F₂ progeny can be derived from the combinations of alleles produced in the Punnett square. For a dihybrid cross like this, the typical ratio is 9:3:3:1 for the four possible phenotypes.