A geneticist crosses a pure-breeding strain of peas producing yellow, wrinkled seeds with one that is pure-breeding for green, round seeds.
What proportion of the F₂ progeny are expected to have yellow seeds? Wrinkled seeds? Green seeds? Round seeds?

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 Mendelian inheritance where one allele is dominant and the other is recessive for each trait.
2. Step 2: Assign alleles to the traits. Let 'Y' represent the dominant allele for yellow seeds and 'y' represent the recessive allele for green seeds. Similarly, let 'R' represent the dominant allele for round seeds and 'r' represent the recessive allele for wrinkled seeds.
3. Step 3: Determine the genotypes 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.
4. Step 4: Perform a dihybrid cross to determine the F₁ generation. Cross YYrr with yyRR. The F₁ progeny will all be heterozygous for both traits (YyRr), producing yellow, round seeds due to the dominance of 'Y' and 'R'.
5. Step 5: Use a Punnett square to analyze the F₂ generation. Cross two F₁ individuals (YyRr × YyRr) to determine the proportions of each phenotype. Calculate the expected proportions for yellow seeds, wrinkled seeds, green seeds, and round seeds based on the combinations of alleles in the Punnett square.

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 (dominant) and green seeds (recessive) are key traits in the pea plants being studied.

Punnett Square

A Punnett square is a diagram used to predict the genotypic and phenotypic ratios of offspring from a genetic cross. By organizing the alleles of the parent plants, it allows for a visual representation of how traits may combine in the F1 and F2 generations. This tool is essential for determining the expected proportions of yellow, green, wrinkled, and round seeds in the progeny.

Phenotypic Ratios

Phenotypic ratios refer to the relative frequencies of different phenotypes in the offspring resulting from a genetic cross. In this scenario, the F2 generation will exhibit a specific ratio of yellow to green seeds and wrinkled to round seeds based on the inheritance patterns. Understanding these ratios helps predict the expected traits in the progeny from the initial cross.