Ok gentle reader - some more food for thought and discussion. I lumped all the myths into one topic to keep but can split them off to different topics if needed... There is some good info here that should generate some nice discussions.
written & prepared by JP Yousha
Myth#1. Purebreds are "weaker" than mutts. Mongrels display more genetic faults and inherited disease traits than any one breed. There are endless sets of statistics to prove this idea is a myth, but they never seem to convince anyone. This is probably due to the combination of the following:
a) Sick and crippled mongrels are less likely to be counted as they are less likely to be among the living, let alone amoung those dogs taken to vet clinic for expensive care.
b) No owner (breeder/vet) ever attributed a disease to a mongrel's breeding.
c) The "Ugly Tourist" syndrome: many healthy pets live quietly on, while one sick Irish Setter or a GSD with hip dysplasia gets more than their share of the focus. Add to this that the better made pets are actually much harder to find & buy for the average pet owner, who sadly tends to, despite all good intentions, to buy from the uninformed if not ourright uncaring breeder.
d) It is romantically inticing to think Nature does a better job of taking care of Her Children than corrupt man does. The fact that "she" doesn't look after any of "her individual children" is obvious only to those who study nature carefully. Sickness, death & dying is just exactly how nature winnows out the numbers to an acceptable level; cruelty by our standards is a standard event in nature-as is suffering. Nature's idea of "controlling" disease is to let the afflicted individuals be born, suffer and die.
Myth#2. Inbreeding is bad; it causes sick and unstable dogs. This goes with the idea (also erronous) than inbreeding doesn't occur in nature. Man's cultural taboos on inbreeding is largely behind all these myths. Inbreeding (linebreeding) & outcrossing are essentially neutral tools used to effect certain ends. It is certainly true that such a thing as inbreeding depression occurs when there is a loss of diversity amoung (some particular) genes in some individuals sometimes in some species, but there is also such a phenomena as outbreeding depression that occurs when you "mess with" a 'good' set of genes by introducing "new blood" into a breeding program. All this is demonstrated in wild as well as zoo populations as well as various domestic animal breeding programs. The point is you just cannot point & say "inbreeding is bad, outcrossing is good;" nature is never than simplistic. Bad breeding decisions often end in sick & unstable animals, but even the best breeding program has individuals who may fall ill. Along with this is the problem of confusing heterozygosity with heterosis (hybrid vigor). The latter is a first generation trait that occurs ONLY in the offspring of two individuals who are themselves from pure(in)bred strains; heterozygosity is a term that relates to whether a given individual has two or one kind of gene (alleles) at any given gene location (locus). The two terms don't even relate to the same level of discussion, and a hybrid is not necessarily "better." Having information on the actual animals in question is what is critical & no formula can replace that all important criteria. The results of any breeding demonstrate the skill (& luck) of the breeder. One of the most inbred lines of dogs in the world has the lowest breed incidence of hip dysplasia and the highest success rate as superior companion dogs--the seeing eye German Shepherd. Which is NOT to say "inbreeding is good;" the old breeder's saw about having to do an outcross every few generations is based on the observation that continuous inbreeding over generations can result in "inbreeding depression;" a phenomena, assumably, having to do with having too much similarity (homozygosity) among certain genes (such as immune genes). The point is one simply does not make breeding or buying choices based on single criteria or "cookbook" formulas--random outcrossing is as deadly as blindly linebreeding--smart breeders make careful selections every generation.
Myth#3. If it is a genetic trait & you have the gene, you are going to get the disease, etc. associated with the trait. This is probably one of the most commonly held & terribly wrong notions people have about genetics. Innate does not mean fated. Having a gene for some trait may be a LONG way from having the trait expressed; you won't get sick necessarily just because you have a gene for a disease. Genes don't "cause" disease; the expression of them may. Of course "carriers" are best identified & eliminated when possible from the breeding stock, but such ideal circumstances may not be available & it's critical to recognise that genetic traits are not like a scarlet letter that brands someone as a "defect," just as it's critical to recognise that we all (& all our dogs) carry defective and even lethal genes. The key, again, is selection: selection as a breeder for what defects are tolerable (i.e. those cosmetic or fashion) and which are not (i.e. those deadly or costly).
Myth#4. If the environment affects the course of a disease/trait, then that proves the trait is not genetic. This is the twin of myth #3 & just about as common. Environment is PART of the genetic inheritance of a person or dog: a certain enviroment is necessary for each and every gene to get "turned on" & expressed. They work TOGETHER, not in opposition. For example, if a dog with genes for hip dysplasia is fed carefully with low protein & low calcium and kept from any real exercise, this dog may express the genes later and with less obvious original bone changes than the pup who eats a ton & runs around unsupervised. Both will end up with arthritis, likely, & both EQUALLY are going to pass on their genes for this crippling disease to their offspring. The first dog is just less "honest" about what sort of genetic parent he really is. Diet & supplements can mask the effects of disease & even control them--think about adult onset diabetes which is usually controlled wholly by diet. But disease controlled by environmental manipulation isn't a cure & the offspring of dogs who need enzyme supplements, for example, are going to display the same kind of pancreatic insufficiency their parents did, even if none of these animals are ever properly diagnosed and their genetic defect isolated or even admitted. As Richard Dawkins says: "A gene's meaning is context dependent."
Myth#5 Genetic means congenital. People still confuse congenital and inherited. Inherited means acquired (genetically) from the parent(s). Congenital means present at birth. Congenital problems can be inherited. But many inherited diseases are not obvious until the animal is mature. That is EXACTLY why we still have problems getting rid of them.
Myth#6 You can buy/breed a dog without undesirable genes. This puppy buyers often demand and some breeders even will promise. Every dog alive likely carries some undesirable traits. In the breeds where this has been systematically studied, every breed individual is likely to carry for 3-5 unwanted traits(gene load). The question is less rather IF you will accept unwanted traits, than WHICH you will decree as most undesirable & which you (and your dog!) can accept and live with. Crooked tails or missing teeth sure beat heart disease and hip dysplasia---all are inherited. Which, if you had a choice, would you choose to carry in your line or have in your dog? This is rather hard for folks to swallow as they believe in myths#3-5 & think your genes are you destiny and that anything genetic is some sort of scarlet letter. We all need to learn a bit more of how biology really works & discard our erroneous ideas not based on the evidence of nature.