Inheritance of color (and other) characteristics is a subject of importance to anyone who breeds living things, since all offspring inherit their unique characteristics from their parent stock. It is the mixing of genetic material (genes) from the parents that gives each individual its own appearance, capabilities, and personality.
A recent article in the Journal of Heredity (a publication of the American Genetic Association) may be of interest to killikeepers, since its subject is Aphyosemion australe Orange. For those who wish to read the original article, see Frankel, J.S., 1997. “Inheritance of body coloration in the lyretail toothcarp (Aphyosemion australe Cyprinodontidae). J. Hered. 88(5): 4445-446.
In essence, Frankel shows that inheritance of the orange body color is determined by two independently non sex-linked genes, recessively expressed. Homozygotes (genotype aabb) are orange. So are fish with genotypes aaB_ and A_bb. All other genotypes (A_B_) are brown (the “wild” type). Thus, one could make double heterozygotes by crossing pure breeding browns (genotype AABB) with pure breeding oranges (aabb) and then intercrossing the heterozygotes to obtain a ratio of 9 brown to 7 orange (roughly 44% orange), a more favorable result than the 3:1 ratio of brown to orange which would occur if the orange trait was controlled by a single recessive gene (such as albinism in many species). Backcrossing the F1 crosses to orange would yield a 3:1 ratio of orange to brown, even more favorable.
Among killifish breeders, it has long been known that the orange color trait was recessive, and that by breeding both brown and orange offspring back to their parents, a population of orange colored AUS could be established. This is how the original color strain was developed.
Many of the existing strains of orange AUS are strong and robust, as are many of the original brown strains. However, in some cases the strains have deteriorated, with decreasing fertility rates and increasing breeding and hatching failures occurring. The time-honored way of dealing with such inbreeding depression is to cross back into the authentic wild stock and then to intercross the F1 progeny, or to backcross to the parents. Frankel’s article shows that this could be practical with orange AUS, yielding a good proportion of orange progeny.
However, any such crosses should be done with stock collected at the same location as the original stock, or as close to its original locale (“Cape Lopez” as possible. Many of the Aphyosemion species are comprised of populations that appear very similar, but are genetically quite different. As killi breeders are very much aware, crossing the “wrong” populations could result in the production of actual hybrids, and sterile offspring.
— G.C.K.A. Newsletter, February 1998