Question

The trait of medium-sized leaves in iris is determined by the genetic condition \(P P^{\prime}\). Plants with large leaves are \(P P\), whereas plants with small leaves are \(P^{\prime} P^{\prime} .\) A cross is made between two plants each with medium-sized leaves. If they produce 80 seedlings, what would be the expected phenotypes, and in what numbers would they be expected? What is the term for this allelic relationship?

Short answer

Answer: The expected phenotypes are 20 large leaves, 40 medium-sized leaves, and 20 small leaves. This allelic relationship is known as "incomplete dominance" or "partial dominance."

Step-by-step solution

Set up the Punnett square

First, we need to set up the Punnett square for both parent plants with medium-sized leaves. Their genetic makeup would be \(P P^{\prime}\).

Fill in the Punnett square

Each cell of the Punnett square should be filled with the results of combining the letters from each parent. Write the dominant allele "P" first in each cell, followed by the recessive allele "P'". $$ \begin{array}{cc|cc} & & \textbf{Parent 1} & \\ & & P & P^{\prime} \\ \cline{2-4} \textbf{Parent 2} & P & PP & PP^{\prime} \\ & P^{\prime} & PP^{\prime} & P^{\prime} P^{\prime} \end{array} $$

Calculate expected phenotypic ratios

Now we need to analyze the results of the Punnett square to find the phenotypic ratios. Use the given genotype information to determine the phenotype of each genotype combination. 1. \(PP\): Large leaves 2. \(PP^{\prime}\): Medium-sized leaves 3. \(P^{\prime}P^{\prime}\): Small leaves We can see in the Punnett square that there is 1 \(PP\), 2 \(PP^{\prime}\), and 1 \(P^{\prime}P^{\prime}\). The ratio is 1:2:1 for large : medium : small leaves.

Determine the expected numbers of each phenotype

There are 80 seedlings produced, so apply the phenotypic ratio to the total of 80 seedlings: 1. Large leaves: \(80 \times \frac{1}{4} = 20\) 2. Medium-sized leaves: \(80 \times \frac{2}{4} = 40\) 3. Small leaves: \(80 \times \frac{1}{4} = 20\) The expected numbers of each phenotype are 20 large leaves, 40 medium-sized leaves, and 20 small leaves.

Identify the allelic relationship term

The term for this allelic relationship is "incomplete dominance" or "partial dominance," as neither allele is completely dominant over the other, resulting in an intermediate phenotype (medium-sized leaves) when both alleles are present in the offspring.