Suppose a population of organisms with 500 gene loci is fixed at half of these loci and has two alleles at each of the remaining loci. How many alleles are found in its gene pool?

Options

A. 250
B. 500
C. 750
D. 1000

Answer

To solve the problem of how many alleles are found in the gene pool of a population with 500 gene loci, where half of the loci are fixed and the other half have two alleles, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Total Number of Gene Loci**:
- The problem states that there are 500 gene loci in total.

2. **Determine Fixed Loci**:
- Half of the loci are fixed. Therefore, the number of fixed loci is:
\[ \text{Fixed Loci} = \frac{500}{2} = 250 \]

3. **Determine Loci with Two Alleles**:
- The remaining half of the loci (also 250) have two alleles. Thus, the number of loci with two alleles is:
\[ \text{Loci with Two Alleles} = 500 - 250 = 250 \]

4. **Calculate Alleles from Fixed Loci**:
- Since the fixed loci have only one allele each, the total number of alleles contributed by the fixed loci is:
\[ \text{Alleles from Fixed Loci} = 250 \times 1 = 250 \]

5. **Calculate Alleles from Loci with Two Alleles**:
- Each of the loci with two alleles contributes two alleles. Therefore, the total number of alleles from these loci is:
\[ \text{Alleles from Loci with Two Alleles} = 250 \times 2 = 500 \]

6. **Calculate the Total Number of Alleles in the Gene Pool**:
- To find the total number of alleles in the gene pool, we sum the alleles from the fixed loci and the alleles from the loci with two alleles:
\[ \text{Total Alleles} = \text{Alleles from Fixed Loci} + \text{Alleles from Loci with Two Alleles} = 250 + 500 = 750 \]

### Final Answer:
The total number of alleles found in the gene pool is **750**.