Multiple alleles can be found only when population studies are made.

Answer

### Step-by-Step Solution

1. **Understanding Multiple Alleles**:
- Multiple alleles refer to the presence of more than two alleles for a genetic trait within a population. Unlike simple Mendelian inheritance, where traits are determined by two alleles (one from each parent), multiple alleles allow for a greater variety of phenotypes.

2. **Example of Multiple Alleles - ABO Blood Group**:
- The ABO blood group system is a classic example of multiple alleles. In this system, there are three alleles: IA, IB, and i (where i represents the O blood type).

3. **Genotypes and Phenotypes**:
- The possible genotypes and their corresponding phenotypes are:
- IAIA or IAi = Blood group A
- IBIB or IBi = Blood group B
- ii = Blood group O
- IAIB = Blood group AB
- Here, IA and IB are both dominant alleles, while i is a recessive allele.

4. **Population Studies**:
- To observe multiple alleles, population studies are essential. In a given population, individuals will exhibit different blood types based on the combination of alleles they inherit.

5. **Conclusion**:
- The statement that "multiple alleles can be found only when population studies are made" is true. This is because the diversity of alleles and their combinations can only be observed when analyzing a group of individuals rather than a single organism.