Genetics: Punnett Square Practice - Predict the offspring of a heterozygous cross.

Here are the solutions to the questions:

QUESTION 4: BASIC AGRICULTURAL GENETICS

4.1
Let S represent the allele for spherical seeds (dominant).
Let s represent the allele for dented seeds (recessive).
The Punnett square for the cross between two heterozygous plants (Ss $\times$ Ss) is:

$$\begin{array}{|c|c|c|} \hline \textbf{Gametes} & \textbf{S} & \textbf{s} \\ \hline \textbf{S} & \text{SS} & \text{Ss} \\ \hline \textbf{s} & \text{Ss} & \text{ss} \\ \hline \end{array}$$

4.1.1. Indicate the fraction of the offspring that will have dented seeds.
Dented seeds have the genotype 'ss'. From the Punnett square, there is 1 'ss' out of 4 total offspring.
The fraction is $\boxed{\frac{1}{4}}$.

4.1.2. Calculate the percentage of heterozygous spherical seeds.
Heterozygous spherical seeds have the genotype 'Ss'. From the Punnett square, there are 2 'Ss' out of 4 total offspring.

$$\text{Percentage} = \left( \frac{2}{4} \right) \times 100\% = 50\%$$

The percentage is $\boxed{50\%}$.

4.1.3. Determine the phenotypic ratio of the F$_1$-generation.

• Spherical seeds (SS, Ss): 1 (SS) + 2 (Ss) = 3
• Dented seeds (ss): 1 (ss) The phenotypic ratio is $\boxed{3 \text{ Spherical} : 1 \text{ Dented}}$.

4.1.4. Give the number of offspring that will look similar to the parents.
The parents are heterozygous (Ss), which means they have spherical seeds.
Offspring with spherical seeds are SS and Ss.
Number of offspring with spherical seeds = 1 (SS) + 2 (Ss) = 3.
The number of offspring similar to the parents is $\boxed{3}$.

4.2

4.2.1. Identify the pattern of inheritance represented by EACH of the following:

a) ILLUSTRATION B: Codominance

b) ILLUSTRATION A: Complete dominance

4.2.2. Justify the answer to QUESTION 4.2.1(b).
In Illustration A, the heterozygous offspring (RW) expresses the phenotype of one of the homozygous parents (RR - black flower), completely masking the trait of the other parent (WW - white flower).

4.2.3. Indicate the genotype of the offspring in ILLUSTRATION B.
The offspring in Illustration B shows both parental traits (black and white stripes) simultaneously.
The genotype of the offspring is $\boxed{\text{RW}}$.