Hybrid vigor

Hybrid vigor, or heterosis, is the improved performance of crossbred offspring compared with their inbred or parental populations. Its magnitude and traits depend on the populations crossed and the genetic basis of the trait.

Dominance hypothesis: A model proposing that favorable dominant alleles from one parent mask harmful recessive alleles from the other. Masking deleterious recessive alleles is a leading explanation for heterosis in many crosses.
Hybrid seed: Seed produced by crossing selected parent lines, often to obtain uniform plants with desirable hybrid traits. Commercial hybrid seed packages heterosis in a reproducible crop product.
Hybrid maize: Maize varieties produced by crossing selected parental lines, commonly to combine uniformity and high yield. Its adoption provides a canonical crop example of deliberate heterosis breeding.
Inbreeding: Mating between genetically related individuals, which increases the chance that offspring inherit identical alleles from both parents. Inbreeding can expose recessive disadvantages that crossing genetically distinct populations may mask.
Genomic prediction: Prediction of genetic merit using genome-wide marker data and statistical models. Breeders use it to estimate cross performance before producing and testing every hybrid.
Overdominance: A genetic effect in which a heterozygote has greater fitness or trait value than either homozygote. This model attributes hybrid advantage to heterozygosity itself, rather than merely masking harmful alleles.
Single-cross hybrid: An offspring population produced by crossing two inbred parent lines. This common crop-breeding design creates uniform hybrids that can express strong heterosis.
Mule: The usually sterile offspring of a male donkey and a female horse. Mules illustrate hybrid advantages in vigor and endurance alongside a major reproductive limitation.
Outbreeding depression: Reduced fitness in offspring from crosses between populations adapted to different environments or with incompatible genetic systems. Crossing does not guarantee vigor; some crosses disrupt local adaptations or coadapted gene combinations.
Genotype-by-environment interaction: A change in the relative performance of genotypes across environments. A hybrid’s advantage can depend on where and under what conditions it is grown or raised.

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