# DBT JRF 2022 — Question 78

Exam: DBT JRF 2022 · Section: B · Topic: Genetics › Genetic Mapping & Recombination Frequency · Difficulty: Medium

## Question

One centimorgan is defined as the genetic distance between two loci with a statistically corrected recombination frequency of:

## Options

- **A.** 0.1%
- **B.** 0.5%
- **C.** 1.0%
- **D.** 5.0%

## Answer

Option C

## Explanation

Centimorgan (cM) — unit of genetic distance: One centimorgan (cM) is defined as the genetic distance between two loci at which recombination (crossing over) occurs with a frequency of 1% per meiosis: $1\,\text{cM} = 1\%\,\text{recombination frequency}$ Physical correspondence: In humans, 1 cM ≈ 1 Mb of DNA on average (highly variable along chromosomes). Maximum observable recombination frequency: 50% (for completely unlinked loci on different chromosomes or very far apart on same chromosome). Loci >50 cM apart appear unlinked. Usage: Genetic linkage maps use cM units to represent the relative order and distance of genes/markers along chromosomes, which is essential for gene mapping and marker-assisted selection. Answer: 1 centimorgan = 1% recombination frequency; represents the genetic distance where crossing over occurs in 1/100 meiotic events.

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