gen-define-genetic-variation-in-a-population-and-give-one-short-668b

Define genetic variation in a population and give one short worked example.

# Genetic Variation in a Population **Definition:** Genetic variation refers to the differences in DNA sequences among individuals within a population. It is the raw material for evolution and occurs due to mutations, sexual reproduction, and gene flow. This variation can exist at different levels—from single nucleotide differences to presence/absence of entire genes. ## Worked Example: ABO Blood Type Consider a population of 100 people with the following blood type distribution: - **Type A:** 40 people - **Type B:** 10 people - **Type AB:** 5 people - **Type O:** 45 people **Genetic basis:** The ABO blood type is controlled by one gene with three alleles: - I^A (codes for A antigen) - I^B (codes for B antigen) - i (codes for no antigen) **Calculating allele frequencies:** - Type A = I^A I^A or I^A i = 40 people - Type B = I^B I^B or I^B i = 10 people - Type AB = I^A I^B = 5 people - Type O = ii = 45 people From Type O, we know there are at least 90 *i* alleles (45 × 2). This population shows **genetic variation** because multiple alleles exist at the ABO locus, producing different phenotypes (blood types) among individuals. This variation could affect disease susceptibility and is maintained in the population through balanced selection.