Question

A variable number of tandem repeats (VNTR) locus has 15 different alleles. The number of genotypes possible in a population for this VNTR is ............

Hint:

The number of genotypes at a locus with \( N \) alleles is given by \( \frac{N(N + 1)}{2} \), accounting for both homozygous and heterozygous combinations.

Answer 1

Correct Answer: 120

Step 1: Understanding the VNTR genotypes.
The number of genotypes in a population depends on the number of alleles at the locus and how these alleles can combine. For a locus with 15 alleles, the genotypes can be formed by any combination of two alleles (one from each parent), including the possibility of having the same allele from both parents (homozygous) or different alleles (heterozygous).

Step 2: Calculating the number of genotypes.
For a locus with \( N \) alleles, the number of genotypes possible is given by the formula: \[ \text{Number of genotypes} = \frac{N(N + 1)}{2}. \] This formula counts both the homozygous genotypes (where both alleles are the same) and the heterozygous genotypes (where alleles are different).
For \( N = 15 \) alleles: \[ \text{Number of genotypes} = \frac{15(15 + 1)}{2} = \frac{15 \times 16}{2} = 120. \]

Step 3: Conclusion.
The number of genotypes possible for this VNTR locus is \( \boxed{120} \).