Learn & Understand

The Gene Pool: How Mendel Met Darwin

An individual has genes; a population has a gene pool — the entire collection of genetic variants circulating in a group, tracked by allele frequencies. This shift in scale, from the individual cross to the whole population, was the key that finally united Mendel's genetics with Darwin's evolution into a single grand theory.

Two Great Ideas, Long Apart

For decades, Darwin's theory of evolution by natural selection and Mendel's laws of inheritance sat awkwardly beside each other. Darwin explained how populations change over time but lacked a mechanism of heredity; Mendel explained heredity but said nothing of evolution. Reconciling them required a new way of thinking about genes — not in single organisms, but across whole populations.

The Gene Pool

The unifying concept was the gene pool: the sum of all the genetic variants, or alleles, present in a population. Instead of asking about one organism's genotype, population genetics asks what fraction of all the alleles in the pool are of each type — the allele frequencies. Evolution, in this view, is simply the change in these frequencies over generations.

The Modern Synthesis

In the early twentieth century, mathematicians and biologists showed that Mendelian inheritance, played out across a gene pool, produces exactly the gradual change Darwin described. Natural selection, mutation, migration, and chance all shift allele frequencies over time. This fusion — the “modern synthesis” — became the backbone of evolutionary biology, uniting genes and evolution at last.

Reading the Pool From Counts

Measuring a gene pool starts with counting genotypes in a sample and working back to allele frequencies. Each individual carries two copies of a gene, so tallying how many carry each combination reveals the proportion of each allele in the whole pool — the fundamental measurement on which nearly all population genetics, and the study of evolution in action, is built.

Calculating Frequencies

To derive allele frequencies from genotype counts, use the Allele Frequency Calculator. Test whether the population is evolving with the Hardy-Weinberg Calculator, and measure its diversity with the Heterozygosity Calculator.