What is the primary source of variation in a population?

Step 1: Analyze the question The question asks for the primary source of variation, meaning where new genetic differences originally come from in a population.

Step 2: Explain the concept Variation is the differences in traits among individuals of a population. Several processes affect it, but they do different jobs:

• Mutation: A change in the DNA sequence. It is the only process that creates brand-new alleles, so it is the ultimate origin of all genetic variation.
• Gene flow: The movement of alleles between populations through migration. It spreads existing variation around but does not create new alleles.
• Natural selection: It acts on existing variation by favouring some traits over others. It reduces or reshapes variation rather than creating it.
• Genetic drift: Random changes in allele frequencies, especially in small populations. It changes the frequency of alleles and often reduces variation.

(Sexual reproduction, through crossing over and independent assortment, shuffles alleles into new combinations. But those alleles first came from mutation.)

Step 3: Solution

1. Ask which option creates new genetic material: only mutation does.
2. Gene flow, natural selection and genetic drift all work with variation that already exists.
3. Therefore, the primary source of variation is mutation.

Step 4: Answer B. Mutation.

Step 5: Exam tip Remember: "Mutation makes it, others move it." Mutation creates variation, gene flow moves it, drift randomly changes it, and selection sorts it. If a JAMB question asks for the "origin" or "ultimate source" of variation, think mutation first.