If enough crosses are made between male flies of the genotype 'Aa' and the female flies of the genotype 'aa' to produce about 1000 offsprings. Which one of the following is the most likely distribution of genotypes in the offsprings?

Options

A. 250 Aa , 750 aa
B. 750 Aa : 250 aa
C. 243 AA : 517 Aa : 240 aa
D. 481 Aa : 519 aa

Answer

To solve the problem of determining the distribution of genotypes in the offspring from a cross between male flies of genotype 'Aa' and female flies of genotype 'aa', we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Genotypes**:
- Male genotype: Aa (heterozygous)
- Female genotype: aa (homozygous recessive)

2. **Set Up the Punnett Square**:
- Create a Punnett square to visualize the potential offspring.
- The male gametes (from Aa) can be either A or a.
- The female gametes (from aa) can only be a.

| | a | a |
|-------|-------|-------|
| **A** | Aa | Aa |
| **a** | aa | aa |

3. **Determine the Offspring Genotypes**:
- From the Punnett square, we see the possible genotypes for the offspring:
- Aa (heterozygous) - 2 squares
- aa (homozygous recessive) - 2 squares

4. **Calculate the Ratio of Genotypes**:
- The ratio of the genotypes is:
- Aa : aa = 2 : 2, which simplifies to 1 : 1.

5. **Calculate the Expected Number of Offspring**:
- If we are producing about 1000 offspring, we can calculate the expected numbers based on the 1:1 ratio:
- Total offspring = 1000
- Expected Aa = 1000 / 2 = 500
- Expected aa = 1000 / 2 = 500

6. **Evaluate the Options**:
- Since the question asks for the most likely distribution of genotypes, we look for an option that closely matches the expected 500 Aa and 500 aa.
- The closest option provided in the question is 481 Aa and 519 aa, which approximates the expected 1:1 ratio.

### Conclusion:
The most likely distribution of genotypes in the offspring is approximately 481 Aa and 519 aa.