# DBT JRF 2020 — Question 117

Exam: DBT JRF 2020 · Section: B · Topic: Genetics · Difficulty: Easy

## Question

What is Single Nucleotide Polymorphism (SNP)?

## Options

- **A.** variation at a single nucleotide position observed in 100% population
- **B.** variation at a single nucleotide position observed in at least 10% population
- **C.** variation at a single nucleotide position observed in at least 1% population
- **D.** variation at a single nucleotide position observed in more than 10% population

## Answer

Option C

## Explanation

Single Nucleotide Polymorphism (SNP) definition: A SNP is a variation at a single nucleotide position in the genome that is present at a frequency of $\geq 1\%$ in a given population (minor allele frequency, MAF $\geq 0.01$ ). This threshold distinguishes common SNPs from rare variants (MAF <1%). The human genome contains approximately 4–6 million SNPs (one every ~500–1000 bp on average). SNPs are the most common type of genetic variation and are used for: GWAS (genome-wide association studies), pharmacogenomics, ancestry analysis (population genetics), forensic identification. A variant at <1% frequency is called a rare variant or private mutation, not a SNP.

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