Evolution and gene frequencies — A/L Biology

What must I remember about Evolution and gene frequencies?

• Microevolution is defined as a change in allele frequencies in a population's gene pool over successive generations.
• Hardy-Weinberg Principle states that allele and genotype frequencies in a population remain constant across generations in the absence of evolutionary forces: p + q = 1 and p² + 2pq + q² = 1.
• Five essential conditions for Hardy-Weinberg equilibrium: Extremely large population size, no gene flow (immigration/emigration), no net mutations, random mating, and no natural selection.
• Mechanisms of microevolution: Natural selection (differential reproductive success), Genetic drift (random fluctuation: bottleneck effect and founder effect), Gene flow, and Mutation.
• Modes of natural selection: Stabilizing selection (favors intermediate variants), Directional selection (favors one phenotypic extreme), and Disruptive selection (favors both extremes over intermediates).

Test yourself (1 minute)

1. Hardy-Weinberg problem-solving algorithm

   ALWAYS calculate q² (frequency of homozygous recessives) first, take the square root to find q, calculate p = 1 - q, then determine 2pq (heterozygote frequency).

2. Genetic drift vs Natural selection

   Genetic drift is purely CHANCE-driven occurring prominently in SMALL populations; natural selection is adaptive and non-random.

3. Speciation concepts

   Allopatric speciation involves geographical isolation barriers; Sympatric speciation occurs within the same geographic area (often via polyploidy in plants).

Practise Evolution and gene frequencies questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 6

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Year 1 · Term 2