D4.1.9 (HL)—Gene pool concept

HL D4.1 turns selection into measurable population genetics. A gene pool changes when allele frequencies shift. Hardy-Weinberg gives a no-evolution baseline; selection graphs, isolated populations, artificial selection, and resistance show how forces move populations away from that baseline.

• all alleles in an interbreeding population
• directional, stabilizing, or disruptive selection favours different phenotype ranges
• p and q calculate allele and genotype frequencies in equilibrium
• selection, mutation, migration, drift, or non-random mating may be acting

HL population-genetics questions ask students to quantify or model evolution. The answer starts with the gene pool and allele frequencies, then uses the model or selection graph to decide whether the population is at equilibrium or being shifted by selection, mutation, migration, drift, artificial selection, or isolation.

• Use gene pool and allele frequency language to define evolution quantitatively.
• Interpret selection graphs and isolated populations as changes in phenotype or allele frequencies.
• Apply Hardy-Weinberg equations and equilibrium assumptions, then explain what deviations mean.