The Pros and Cons of Inbreeding in Cats

"Heterosis" is the scientific term for hybrid vigor. It is possible that there are "bad" genes which produce less vigorous individuals when in the homozygous state because good genes have been bred out along with the undesirable characteristics; theoretically the bad genes could be bred out, but in practice this doesn't seem to happen. The other theory is simply that you simply need to have a mixture of two different genes to get the desired effect as they somehow complement each other; highly inbred animals lack this diversity and have poorer immune systems.

"Sex-linked" refers to a trait which is passed on, or determined by, a particular gender. In Abyssinian cats there are several versions of the red color. One is sex-linked i.e. a male cat only needs one copy of the gene, but a female needs two copies of the gene to produce the red color.

Natural Occurrence of Inbreeding

This is not to say that inbreeding does not occur naturally. A feral colony which is isolated from other cats, by geographical or other factors, can become very inbred especially if a dominant male mates with his sisters, then with his daughters and grand-daughters. When he is deposed it will most likely be by his own son or grandson which therefore continues the inbreeding. The effect of any deleterious genes becomes noticeable in later generations as the majority of the offspring inherit these genes. Scientists have discovered that cheetahs, even if living in different areas, are genetically very similar. Possibly disease or disaster drastically reduced cheetah numbers in the past creating a genetic bottleneck. All modern day cheetahs may be descended from a single surviving family unit hence their genetic uniformity.

In the Cheetah, the lack of genetic diversity makes them susceptible to disease since they lack the ability to resist certain viruses. Extreme inbreeding affects their reproductive success with small litter sizes and high mortality rates. Some scientists hope that the appearance of the "King Cheetah", characterized by its blotched markings, means that the Cheetah can develop a healthier gene-pool through mutation (provided man doesn't wipe them out in the meantime). Mankind has contributed to the loss of diversity by sport-hunting cheetahs and reducing the number of available mates. Hunters preferred to shoot unusual specimens (i.e. genetically diverse ones) for the trophy room and this previously included long-haired "woolly cheetahs" and gray/blue cheetahs indicating much greater genetic diversity in the past.

The wolf was once widespread throughout North American, but many of the remaining packs are isolated and have become inbred. The isolation/inbreeding problem has become so acute that conservationists have taken wolves from one area and introduced them into a another area to revitalize the gene pool. In some areas, the choice of mates is so reduced that wolves have resorted to mating with domestic dogs - an extreme form of outcrossing called hybridization. A similar situation in Scotland where the Scottish Wildcat mates with domestic cats is threatening to wipe out the wildcat as domestic cat genes become more widespread. These are two cases where outcrossing (following, and followed by, inbreeding) may lead to extinction of a species (analogous to loss of type in domestic breeds).

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