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

Based on Mendel's principles of segregation and independent assortment, a testcross between F1 generation pea plants (genotype RrYy, phenotype round yellow seeds) resulting from a cross between plants with round, green seeds (genotype RrYy) and plants with wrinkled, yellow seeds (genotype rrYY), will yield two potential phenotypes. These are: 1. Round and yellow seeds: This results from the dominant traits for round shape (R) and yellow color (Y). 2. Wrinkled and yellow seeds: This results from the recessive trait for wrinkled shape (r) and the dominant trait for yellow color (Y). Hence, no green seeds will be produced because the testcross parent is homozygous dominant for yellow (YY).

Step-by-step solution

Identify the genotypes of the parents

First, let's identify the genotypes of the parent plants. Round seeds are dominant (R) over wrinkled seeds (r), and yellow seeds are dominant (Y) over green seeds (y). The genotype of the pea plant with round, green seeds is RrYy since it passed on the gene for round seeds and one for green seeds. Likewise, the genotype of the pea plant with wrinkled, yellow seeds is rrYY since it passed on the gene for wrinkled seeds and one for yellow seeds.

Determine the F1 generation genotypes

Next, we'll determine the genotypes of the F1 generation by crossing the parent plants. We can use a Punnett square to visualize this cross: Parent 1: RrYy Parent 2: rrYY Punnett Square: ``` RY Ry rY ry +---------------- rY | RrYY RrYy rrYY rrYy rY | RrYY RrYy rrYY rrYy ``` So, the F1 generation plants all have the genotype RrYy, with round (R) and yellow (Y) seeds.

Perform the testcross

A testcross is done by crossing the F1 generation (RrYy) with a homozygous recessive genotype for both seed shape and seed color (rryy). Let's perform this testcross using another Punnett square: F1 plant: RrYy Testcross plant: rryy Punnett Square: ``` Ry rY Ry ry +---------------- ry | Rryy rryy Rryy rryy ry | Rryy rryy Rryy rryy ```

Predict the resulting phenotypes

Now, let's look at the resulting genotypes from the testcross and determine their corresponding phenotypes: 1. Rryy: Round and yellow seeds (dominant R and Y) 2. rryy: Wrinkled and yellow seeds (recessive r and dominant Y) Thus, the results of the testcross will produce offspring with either round and yellow seeds or wrinkled and yellow seeds. There will be no green seeds because the testcross parent is homozygous dominant for yellow (YY).