Outbreeding depression This phenomenon can occur in two ways. One way is by the "swamping" of locally adapted genes in a wild population by straying from, for example, a hatchery population. In this case, adaptive gene complexes in wild populations are simply being displaced by the immigration of genes that are adapted to the hatchery environment or to some other locality. For example, selection in one population might produce a large body size, whereas in another population small body size might be more advantageous. Gene flow between these populations may lead to individuals with intermediate body sizes, which may not be adaptive in either population. A second way outbreeding depression can occur is by the breakdown of biochemical or physiological compatibilities between genes in the different populations. Within local, isolated populations, alleles are selected for their positive, overall effects on the local genetic background. Due to nonadditive gene action, the same genes may have rather different average effects in different genetic backgrounds--hence, the potential evolution of locally coadapted gene complexes. Offspring between parents from two different populations may have phenotypes that are not good for any environment. It is important to keep in mind that these two mechanisms of outbreeding depression can be operating at the same time. However, determining which mechanism is more important in a particular population is very difficult. A hatchery is a man-made farm for fish, used to cultivate and breed a large number of fish in a enclosed environment regulary as opposed to going out and finding the fish naturally. ... An allele is any one of a number of viable DNA codings of the same gene (sometimes the term refers to a non-gene sequence) occupying a given locus (position) on a chromosome. ...
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inbreeding depression heterosis Inbreeding Depression is reduced fitness in a given population as a result of breeding of related individuals. ... Heterosis is increased strength of different characteristics in hybrids; the possibility to obtain a better individual by combining the virtues of its parents. ...
References
INBREEDING DEPRESSION AND OUTBREEDING DEPRESSION by Michael Lynch http://www.nwfsc.noaa.gov/publications/techmemos/tm30/lynch.html
Although divergence between pink salmon broodlines is large and outbreedingdepression might be expected in such unlikely hybrids, the results document the occurrence of outbreedingdepression in salmon and signal caution in making management and aquacultural decisions that may create the possibility of outbreedingdepression in self-sustaining or cultured populations.
Outbreedingdepression resulting from additive genetic effects would be expected to appear in first generation hybrids (F1), like the depression observed in tolerance to DDT in F1 mosquitoes or the increased susceptibility of F1 coho salmon to the parasite Ceratomyxa shasta.
Resultant outbreedingdepression may not occur until the second or later generations when assortment of alleles at different loci takes place.
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