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Breeder Notebook: Myth-information

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They reproduce with amazing fecundity, thrive in all climates, and gather proponents wherever they go. Are they an amazing new dog breed? No, they’re the myths of the dog breeding world – and they’re alive and well.

Myth: Breeding a flighty bitch will steady her temperament. If a bitch has a poor temperament, breeding is not going to improve it. It’s only going to increase the risk of producing more dogs with flighty temperaments.

Myth: Breeding a slab-sided bitch will expand her ribcage. Again, if a bitch needs to be bred in order to develop some trait (which seems doubtful at best), then perhaps you should rethink your breeding program.

Myth: Any dog carrying an undesirable gene should be neutered. Every dog carries genes for undesirable traits, including some for health problems (it’s been calculated each dog carries three to five such genes, on average). If they were all neutered there would be no more dogs. The secret is to avoid doubling up on such genes when breeding. As more DNA tests are developed for different genes in different breeds, this will become increasingly possible. If dogs identified as carriers are bred only to dogs tested clear of the gene, then the progeny should only be carriers and clears, not affecteds.

Myth: Repeat litters are never as good as the first ones. Proponents of this myth even offer a pseudo-scientific explanation of why this is so: “To avoid inbreeding in the population, nature makes sure the second litter isn’t as good.” How would nature accomplish this? According to the theory, the eggs will only allow inferior sperm to fertilize them if they (the eggs) recognize the sperm as coming from the same sire the bitch was bred to last time. So unless the bitch is bred to a different stud in between, the offspring will only be sired by the inferior sperm. By this logic, the second-born children of humans would all be inferior unless the mother had been fooling around with another man!

To set the record straight, no mechanism has ever been identified by which an animal or its eggs could recognize sperm as derived from the same male as the last time she was impregnated. Nor has any way for eggs to determine sperm carrying good dog-show traits versus bad dog-show traits ever been identified. True, repeat breedings often aren’t as nice as first breedings. But that’s more likely due to statistical chance.

Breeders are most likely to repeat breedings that have extraordinary puppies. The extraordinary qualities of these puppies depended in part on the random shuffle of genes in the eggs and sperm. The chance of getting such a fortuitous chance shuffle twice in a row is lower than the chance of getting an “average” shuffle. Thus, the litter quality will tend to regress toward the mean.

Myth: The best breeding is between an uncle and niece (or aunt and nephew). No explanation has been offered as to why this formula is promoted. Sure, some people have gotten nice puppies from such breedings – just as many have gotten poor puppies. Is it just any uncle and niece? No. As in any breeding, the quality of the individuals is a primary consideration. There are no ready-made formulas for dog breeding.

Myth: Tail lines, particularly bitch tail lines, are the secret to good breeding. Here’s an example of a little knowledge being worse than none at all. A tail line refers to the line on the very bottom (dam to granddam to great-granddam) or very top (sire to grandsire to great-grandsire); the only lines in which the sex is always the same. The logic presented for tail line breeding is that the bitch has two X chromosomes, while the male has an X and a Y (True). Further, the tiny Y chromosome carries very little genetic information on it, whereas the larger X chromosome carries true genetic information (True). A male must get his X chromosome from his dam (True). A bitch must get one of her X chromosomes from her sire (True). After that, the logic falls apart. The myth asserts that the way to get a well-producing bitch is to make sure her sire had a nice dam. True, the best way to get good dogs or good producers is to have good ancestors. But the X chromosome has little to do with it. For one thing, it is but one of 39 chromosomes. While it may carry some traits of importance to conformation, it’s no more likely to than any of the other 38 chromosomes that somehow get forgotten in this theory. For another, even if you knew which traits were carried on the X chromosome, the expression of those traits differs depending on whether it’s in a male a or bitch. In males, what you see is what you get; the traits carried on that single X chromosome are expressed. In bitches, it’s not. At some point during development in each cell line, one or the other of the two X chromosomes is randomly inactivated, so that bitches are actually mosaics of cells derived from one or the other X chromosome.

The same reasoning applies to the myth that great sires carry great sire tail lines. The argument goes that because the Y chromosome is passed from father to son, genetic material from the Y chromosome will be concentrated in the fortunate male descendant. The problem is that virtually no traits except a few concerning male reproduction have been traced to the Y chromosome in any species, let alone dogs.

Myth: Inheritance is either/or, never a compromise. Again, this is where that little bit of knowledge thing gets people in trouble. True, many traits are inherited in a yes-no, dominant-recessive way. But many more are inherited in an additive way, such that progeny is often intermediate between the parental types.

When you hear about a breeding theory that seems too easy or too far-fetched, it probably is. Find a reputable source with scientific data before embracing such theories as your own.

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