Q.51
A variable number of tandem repeats (VNTR) locus has 15 different alleles. The number of genotypes possible in a population for this VNTR is ________.
Introduction
In genetics, understanding VNTR locus 15 alleles genotypes is crucial for DNA profiling and competitive exams like CSIR NET. A Variable Number of Tandem Repeats (VNTR) locus with 15 different alleles produces exactly 120 possible genotypes in a population, calculated via standard combinatorial genetics [memory:1].
VNTR Basics
Variable Number Tandem Repeats (VNTRs) are DNA regions with short sequences repeated multiple times in tandem, varying in repeat number across individuals, creating distinct alleles. Each allele differs by repeat count, making VNTRs useful in genetics for DNA fingerprinting and population studies. In diploid organisms like humans, individuals inherit one allele per chromosome at a locus, forming genotypes from allele pairs [conversation_history:10].
Genotype Calculation
Genotypes include homozygous (identical alleles, like A1/A1) and heterozygous (different alleles, like A1/A2) forms.
Heterozygous genotypes = n(n−1)/2 = 15×14/2 = 105
Total Genotypes: 15 + 105 = 120
Direct formula: n(n+1)/2 = 15×16/2 = 120 [memory:2].
Step-by-Step Calculation
Homozygous Genotypes
- One per allele (A1/A1 to A15/A15)
- Total = 15
Heterozygous Genotypes
- Unique pairs without regard to order
- Combinations: 15×14/2 = 105
Total Genotypes
Common Errors to Avoid
❌ Mistake 2: 15×14 = 210 (permutations, not combinations)
✅ Correct: 15(15+1)/2 = 120
Applications in Genetics
VNTR analysis supports biodiversity studies and disease mapping due to extensive allelic diversity. These hypervariable loci enable high-resolution genotyping for forensics and paternity testing [conversation_history:10].
