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Haldane's Sieve

Explain why new beneficial mutations that are dominant fix far more often than recessive ones — because while rare an allele sits almost only in heterozygotes, so selection sees a dominant from its first copy but is blind to a masked recessive, which usually drifts to loss before homozygotes form.

Version
v3 · 2026-09-28 · History · 5 corrections
Domain-specific #
480
Domain group
Natural Sciences
Origin domain
Biology & Ecology
Subdomain
Population Genetics and Adaptation → Biology & Ecology

Core Idea

Haldane's sieve (Haldane, 1927) is the population-genetic result that new beneficial mutations fix far more readily when dominant than when recessive. The mechanism is visibility: while rare, an allele exists almost only in heterozygotes, so a dominant one's advantage is expressed and selected from the first copy, while a recessive one is masked and drifts as though neutral, usually lost before homozygotes form. The population acts as a filter, and the fixed record of adaptation is a dominance-biased sample.

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The Hidden-Helper Strainer

Sometimes a baby animal is born with a brand-new helpful change. If the change shows right away, it helps that animal, and the change spreads. If it stays hidden, nobody can tell it is helpful, so it usually gets lost by bad luck before it can spread. Haldane's Sieve is like a strainer that keeps the showing-off changes and lets most hidden ones fall through.

The Dominant Gene Filter

Most animals and plants get two copies of each gene, one from each parent. When a new helpful gene change first appears, it sits in just a few individuals, each with only one copy. If the change is dominant, one copy is enough to show its benefit, so nature favors it and it spreads. If it is recessive, it needs two copies to show, so at first it is invisible and usually disappears by chance. Haldane's Sieve is this filter: it lets dominant helpful changes through and catches most recessive ones.

Dominance Bias in Adaptation

Haldane's Sieve (Haldane, 1927) says that a new beneficial mutation in a diploid population is much more likely to survive and spread to fixation if it is dominant rather than recessive. While a new allele is rare, it sits almost only in heterozygotes, individuals with one copy. A dominant allele shows its advantage in heterozygotes, so natural selection boosts it immediately; a recessive one is hidden and drifts as if neutral, usually being lost by genetic drift. So the adaptations we actually see are biased toward dominant effects. The sieve is weaker when adaptation uses alleles already present at some frequency (standing variation), because homozygotes already exist. It is also absent in very small populations, where drift loses almost everything, and gets sharper in larger ones.

 

Haldane's Sieve is Haldane's 1927 population-genetic result that new beneficial mutations in diploids fix far more often when dominant than when recessive. The mechanism is visibility to selection: a rare allele occurs almost entirely in heterozygotes, where a dominant allele's advantage is expressed but a recessive allele's is masked. The recessive allele therefore drifts as if neutral, and most copies are lost before homozygotes become common enough for selection to act, giving it a much lower fixation probability than a dominant allele with the same selection coefficient. As a result, alleles that produce selective sweeps are enriched for dominant effects relative to the input distribution of beneficial mutations. The sieve applies fully to hard sweeps from a single new mutation but is weak or absent for soft sweeps from standing variation, where the allele already starts at a frequency with homozygotes present. It is one theoretical pillar of the hard-versus-soft sweep distinction, seen for example in pesticide resistance from new mutation versus from a pre-existing resistant minority. Its strength depends on population size: in very small populations drift swamps selection for both kinds of allele, whereas in larger populations a dominant allele keeps roughly a 2s establishment chance while a recessive one must drift through an ever-wider low-frequency range. This means small populations have reduced access to recessive beneficial variation from new mutation, a concern in conservation genetics.

Scope of Application

Haldane's sieve lives within the population-genetics and adaptation subfields of biology, ranging over diploid sexually-reproducing populations under selection — its load-bearing content being irreducibly quantitative (dominance coefficient, h·s selection, ½N_e initial frequency).

  • Adaptive evolution theory — fixed alleles skew toward dominants relative to mutational input.
  • Crop genetics — dominant resistance genes spread faster via single-cross introgression.
  • Pesticide resistance — spreading alleles in diploid pest populations are dominance-biased on the target trait.
  • Conservation genetics — small populations retain fresh recessive variation poorly.
  • Hard-versus-soft-sweep theory — the reason the two sweep classes differ in dominance.

Clarity

The sieve dissolves a puzzle: the dominance composition of alleles that actually fix looks unlike the mutational input — too many dominants. It needs no special mechanism, only the fact that a rare allele sits almost only in heterozygotes. The clarifying move separates the mutational input from the fixed record and names the population as the filter between them, so a sweep's genomic signature is understood as a dominance-biased sample, not a random draw. It also makes crisp the new-mutation-versus-standing-variation boundary.

Manages Complexity

The fate of a new allele depends on a tangle of interacting quantities — dominance, selection coefficient, effective population size, mutation rate, initial frequency — through stochastic dynamics no one wants to integrate by hand. The sieve compresses that joint dependency into one qualitative principle and turns the rest into readable regime switches: one boundary condition (new mutation versus standing variation) decides whether the sieve bites, and population size fixes its strength. The analyst reads the outcome off that compact set.

Abstract Reasoning

The sieve runs on three parameters — dominance, the new-mutation-versus-standing-variation boundary, and population size. A diagnostic move infers a hidden property of the mutational process from the swept record (a dominance-biased sample); an interventionist move raises a recessive's frequency past the homozygote-forming range to bypass the filter; a boundary-drawing move places a case as hard sweep or soft sweep before predicting; and a predictive move forecasts the dominance difference between the two sweep classes.

Knowledge Transfer

Within population genetics the sieve transfers as mechanism across all diploid sexually-reproducing organisms, because the cargo is one quantitative result — effective selection on a rare allele scales with h·s, and recessives drift to loss before homozygotes form. It carries directly into crop genetics, pesticide resistance, conservation genetics, and the hard-versus-soft-sweep literature, plus adjacent masked-at-low-frequency settings. Beyond diploid selection the quantitative machinery does not travel; only the bare visibility intuition does, and the genuinely portable content is the more general selection-visibility pattern — a selector samples only what is expressed — a candidate parent riding alongside genetic drift.

Relationships to Other Abstractions

Local relationship map for Haldane's SieveParents appear above the current abstraction, mutual partners to the right, and children below. Node labels state whether each abstraction is prime or domain-specific; colors identify relation types.Haldane's SieveDOMAINPrime abstraction: Selection-Visibility Gate — is a kind ofSelection-Visib…PRIME

Current abstraction Haldane's Sieve Domain-specific

Parents (1) — outgoing typed relations

  • Haldane's Sieve is a kind of Selection-Visibility Gate Prime

    Haldane's sieve is selection visibility specialized to a new beneficial allele whose heterozygous expression scales with dominance while it is rare.

Hierarchy path (1) — routes to 1 parentless root

Neighborhood in Abstraction Space

Haldane's Sieve sits in a moderately populated region (53rd percentile for distinctiveness): it has near-neighbors but no dense thicket of look-alikes.

Family — Population Genetics & Selection (11 abstractions)

Nearest neighbors

Computed from structural-signature embeddings · 2026-10-25