[A]: When doing genetics problems, firs de- cide the appropriate key and then determine the genotype and gametes for both parents.
[R]: It is necessary to keep in mind that al- though an individual has two alleles for each trait, each gamete has only one allele for each trait

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

To solve the genetics problem presented, we will follow a systematic approach based on the information provided in the video transcript. Here’s a step-by-step breakdown:

### Step 1: Identify the Traits and Alleles
- **Traits**: We are dealing with two traits: Yellow (dominant) and Green (recessive).
- **Alleles**:
- Yellow is represented by the dominant allele (Y).
- Green is represented by the recessive allele (y).

### Step 2: Determine the Genotypes of the Parents
- For the yellow trait, the possible genotypes are:
- Homozygous dominant: YY
- Heterozygous: Yy
- For the green trait, the genotype is:
- Homozygous recessive: yy

Assuming we are crossing a homozygous dominant yellow (YY) with a homozygous recessive green (yy):
- **Parent 1 (Yellow)**: YY
- **Parent 2 (Green)**: yy

### Step 3: Determine the Gametes
- Each parent will produce gametes that carry one allele for each trait.
- **Gametes from Parent 1 (YY)**: Y (only one type of gamete since both alleles are the same)
- **Gametes from Parent 2 (yy)**: y (only one type of gamete since both alleles are the same)

### Step 4: Perform the Cross
- When we perform the cross between the gametes of both parents:
- Gamete from Parent 1 (Y) combines with gamete from Parent 2 (y).
- The resulting genotype of the offspring will be:
- Yy (all offspring will be heterozygous)

### Step 5: Phenotypic Ratio of the Offspring
- Since Y is dominant over y, all offspring (Yy) will exhibit the yellow phenotype.
- Therefore, the phenotypic ratio is:
- 100% Yellow progeny.

### Step 6: Self-Fertilization of the Offspring
- If we self-fertilize the F1 generation (Yy x Yy), we can determine the ratios in the next generation:
- Possible gametes from Yy: Y and y.
- Punnett Square for Yy x Yy:
- YY (25%)
- Yy (50%)
- yy (25%)
- Resulting phenotypic ratio in the second generation:
- 75% Yellow (YY and Yy) and 25% Green (yy).

### Conclusion
- The assertion (A) is true: We first decide the appropriate key (dominant and recessive traits) and determine the genotypes and gametes.
- The reason (R) is also true: Each gamete carries only one allele for each trait.
- Therefore, both A and R are true, and R is the correct explanation of A.