Partial dominance hypothesis¶
A population-genetic hypothesis explaining inbreeding depression as increased homozygous expression of deleterious alleles whose harmful effects are recessive or partially recessive in heterozygotes.
Core Idea¶
The partial dominance hypothesis explains inbreeding depression as increased homozygous expression of deleterious alleles whose harmful effects are recessive or partially recessive in heterozygotes. Inbreeding raises identity by descent and homozygosity, exposing more masked genetic load and reducing fitness or a related trait.
With continued inbreeding and selection, harmful alleles may be purged from some lines, fixed in others, or contribute to line extinction. The hypothesis therefore predicts both an initial decline and possible longer-run changes in surviving line means and allele frequencies.
Scope of Application¶
The hypothesis is evaluated in population genetics, conservation, breeding, and experimental inbreeding studies. It applies where segregating deleterious variants and dominance relations plausibly affect measured fitness components.
It differs from overdominance, which attributes depression to loss of superior heterozygous genotypes. Environmental deterioration, demographic change, drift, and mating structure can also lower performance. Outcrossing recovery alone is compatible with more than one mechanism and does not uniquely prove partial dominance.
Clarity¶
The abstraction separates trigger, genetic substrate, expression relation, and consequence. Increased homozygosity is the trigger; partially recessive deleterious load supplies the causal material; homozygous expression supplies the mechanism; and reduced fitness supplies the observation to explain. This chain generates specific tests beyond a correlation between relatedness and poor performance.
It also clarifies the meaning of purging. A surviving line can improve because selection removed exposed harmful alleles, while the collection of lines can improve because the most affected lines disappeared. Those processes have different evidential signatures and conservation implications. Failure to observe recovery does not alone refute the mechanism, because drift, small population size, linkage, and continuing fixation can oppose purging.
Manages Complexity¶
Many loci of small effect, dominance coefficients, linkage, selection, and stochastic line loss contribute to inbreeding depression. The hypothesis compresses them into a directional mechanism: masked harm becomes exposed. That simplification supports comparison but should not erase heterogeneous effects, extinct lines, or uncertainty about the underlying allele distribution.
Abstract Reasoning¶
Measure fitness under known pedigrees or genomic inbreeding across replicate lines and generations. Model the expected increase in homozygosity, seek evidence about deleterious variants and dominance, and track purging, fixation, and differential survival. Compare predictions with overdominance and non-genetic alternatives. Interpret cross-line heterosis only alongside evidence capable of discriminating the competing causes.
Knowledge Transfer¶
The causal logic transfers across taxa and traits when inbreeding, load, dominance, and fitness are measured comparably. Parameter estimates do not move unchanged across populations or environments. In other genetic contexts, “partial dominance” may describe an allele’s phenotype without invoking this population-level account. The hypothesis transfers only when masked deleterious variation explains the response to increased homozygosity. That explicit requirement prevents a familiar label from replacing direct comparison among plausible genetic and environmental causal mechanisms.
Neighborhood in Abstraction Space¶
Partial dominance hypothesis sits in a sparse region of the domain-specific corpus (96th percentile for distinctiveness): few abstractions share its structure, so a faithful description tends to retrieve it precisely.
Family — Selection, Speciation & Experimental Evolution (22 abstractions)
Nearest neighbors
- Wallace Effect — 0.79
- Hardy-Weinberg Principle — 0.78
- Vicar of Bray (scientific hypothesis) — 0.77
- Haldane's Sieve — 0.77
- Fixation (population genetics) — 0.77
Computed from structural-signature embeddings · 2026-10-08