Heterosis
![A mixed-breed dog](/Images/godic/202501/18/MixedBreedFace1_wb2717.jpg")
![Genetic basis of heterosis.
Dominance hypothesis. Scenario A.
Fewer genes are under-expressed in the homozygous individual. Gene expression in the offspring is equal to the expression of the fittest parent.
Overdominance hypothesis. Scenario B.
Over-expression of certain genes in the heterozygous offspring.
(The size of the circle depicts the expression level of gene A)](/Images/godic/202501/18/Heterosis.svg2717.png")
Heterosis, hybrid vigor, or outbreeding enhancement, is the improved or increased function of any biological quality in a hybrid offspring. The adjective derived from heterosis is heterotic.
An offspring exhibits heterosis if its traits are enhanced as a result of mixing the genetic contributions of its parents. These effects can be due to Mendelian or non-Mendelian inheritance.