D4.1.10 (HL)—Allele frequencies

Allele frequencies describe how common each allele is in a population gene pool in evolving populations in evolving populations in evolving populations.

Allele frequency is the proportion of all gene copies represented by one allele; geographically isolated populations can have different frequencies.

Database step	Record before comparing populations
Choose one human variant	Gene, rsID and reference/alternate alleles
Select population or subpopulation data	Geographic identity and sample size
Read allele counts/frequencies	Same allele and same data field in every population
Compare	Difference, direction and uncertainty; do not infer a cause from frequency alone

The mapped local textbook uses human LPL variant rs268: dbSNP reports global A = 0.983727 and G = 0.016273 and provides subpopulation frequency data. Use those subpopulation fields to compare geographic groups rather than treating the global value as every population's value.

Isolation reduces gene flow, so drift and different selection pressures can make allele frequencies diverge over generations.

Compare the same variant and compatible datasets. A geographic frequency difference is evidence of population structure, not by itself proof of natural selection.

How it is assessed

This objective is assessed through structured response, commonly using State / Deduce.

Command terms

State / Deduce

What earns marks

Build the answer around this relationship: Allele frequency is a proportion within the population gene pool.

Representative question

[Maximum number: 1]

Define allele frequency.

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.

Concept essentials

Allele frequency is a proportion within the population gene pool.
For two alleles, p plus q equals one.
A change in allele frequency is evidence of evolutionary change.

D4.1.10 (HL)—Allele frequencies

Compare Geographic Allele Frequencies with Databases

Allele frequencies

Assessment in practice

Retrieve the HL Population Genetics Route

HL Population Genetics

Concept essentials

Question 1