Question

Mendel crossed peas with round, green seeds with peas having wrinkled, yellow seeds. All \(\mathrm{F}_{1}\) plants had seeds that were round and yellow. Predict the results of testcrossing these \(F_{1}\) plants.

Short answer

Answer: The phenotypic ratios of the offspring are 50% round, green seeds and 50% wrinkled, yellow seeds.

Step-by-step solution

Identify the traits and their alleles

In this problem, we have two traits: seed shape (round vs. wrinkled) and seed color (green vs. yellow). Let's assign a letter to represent each trait's dominant and recessive alleles: - Round (dominant): R - Wrinkled (recessive): r - Yellow (dominant): Y - Green (recessive): y The parent plants are: - Round, green seeds: RRyy - Wrinkled, yellow seeds: rrYY

Determine the genotypes of \(\mathrm{F}_{1}\) plants

To find the genotype of the \(\mathrm{F}_{1}\) plants, we perform a cross between the parent plants, using a Punnett square: ``` RY Ry rY ry RY RRYY RRYy rrYY rrYy Ry RRYY RRYy rrYY rrYy rY RRyy RRyy rryy rryy ry RRyy RRyy rryy rryy ``` All \(\mathrm{F}_{1}\) plants have the genotype RrYy: round and yellow seeds.

Perform a testcross with the \(\mathrm{F}_{1}\) plants

A testcross involves crossing the \(\mathrm{F}_{1}\) plants with an individual that is homozygous recessive for both traits (rryy). This allows us to determine the possible genotypes of the offspring: - \(\mathrm{F}_{1}\) genotype: RrYy - Testcross genotype: rryy

Construct a Punnett square for the testcross

Perform a cross between the \(\mathrm{F}_{1}\) plants (RrYy) and the testcross plants (rryy): ``` Ry rY Ry ry ry Rryy rryy Rryy rryy ry Rryy rryy Rryy rryy ry RRyy rrYY RRyy rrYy ry RRyy rrYY RRyy rrYy ```

Determine the phenotypes of the offspring

Based on the Punnett square obtained in Step 4, the resulting genotypes and phenotypes of the offspring are: 1. RRyy: round, green seeds (25%) 2. Rryy: round, green seeds (25%) 3. rrYY: wrinkled, yellow seeds (25%) 4. rrYy: wrinkled, yellow seeds (25%) Hence, the predicted phenotypic ratio for the offspring resulting from testcrossing these \(\mathrm{F}_{1}\) plants is 50% round, green seeds, and 50% wrinkled, yellow seeds.