Introgression

Simple hybridization results in a relatively even mixture; gene and allele frequencies in the first generation will be a uniform mix of two parental species, such as that observed in mules.

Introgression, on the other hand, results in a complex, highly variable mixture of genes, and may only involve a minimal percentage of the donor genome.

[8] There is evidence that introgression is a ubiquitous phenomenon in plants and animals,[9][10] including humans,[11] in which it may have introduced the microcephalin D allele.

[13] Introgressive hybridization has also been shown to be important in the evolution of domesticated crop species, possibly providing genes that help in their expansion into different environments.

[citation needed] One important example of introgression has been observed in studies of mimicry in the butterfly genus Heliconius.

When the locus is not important in the color pattern expression, the two species are phylogenetically distant because there is no introgression at such loci.

For instance, a species of iris from southern Louisiana has been studied by Arnold and Bennett (1993) regarding the increased fitness of hybrid variants.

[23] An introgression line (IL) is a crop species that contains genetic material artificially derived from a wild relative population through repeated backcrossing.

[24] Lineage fusion is an extreme variant of introgression that results from the merging of two distinct species or populations.