Regarding the frequent accusation of Pedigree dogs being genetically compromised by disease and the frequent assertion of mixed breeds and mongrels being healthier,  I have searched for information on the incidence of genetic disease on the least interbred population with the largest gene pool known - Humans.

The information below, refers only to disorders/diseases with a single gene at fault.  I couldn't find figures for disorders/diseases with multiple genes at fault, but they must be out there somewhere.      Nevertheless, I find it astonishing that 60% of  'older' people will suffer from genetic or partly genetic disease.     What happened to all that 'hybrid vigour'  the RSPCA and Vets are talking about ???

We all carry genes that are potentially hazardous. Some are hidden in recessive form and we may never know that we carry them. Some will only exert their influence through interactions with environmental triggers. Others are mIncidence of anifest from or even before our birth. A working party of the Royal College of Physicians has estimated that 2-3% of births result in babies with either congenital or genetically-determined abnormalities.

This means that approximately 13 000 births a year in the UK are so affected. Some conditions manifest themselves later in life. 5.5% of the population will have developed a genetic disorder by age 25. Later in life, this figure rises to approximately 60% if we include conditions in which genetics plays some role. The incidence of many Mendelian disorders varies from one ethnic group to another.

http://www.geneticalliance.org.uk/education3.htm

Going by what my sister and I suffer from, both now in the later stages of our lives, my 'outcross' parents have passed on loads of problems!!!!   LOL

Fact is however, that it's not every breeder of purebred animals knows enough about how dominant and recessives work!   And seems to me they often don't even look at the individual dogs with educated eyes, never mind the pedigrees before rushing in - often to use the most winning male of the day on their bitches.   In my own breed, recessives are where so many of the problems we see in the breed lurk.    And these's no doubt a little knowledge and a lot of research would maybe avoid much of what might appear.    Has to be said the best laid plans can go wrong however!!

For me, much as once into a winning formula it's hard to outcross but outcrossing is definitely needed at some point, to avoid fixing problems as well as traits that are wanted.   This is a million miles away from mixing two different breeds 'to improve vigour' however.  Especially when it's being done by BYBs who are only interested in one thing - INCOME.  

Although a top winning male, being allowed to be used too much, can influence the direction a breed takes, and his over-use will reduce the gene pool, most breeds, I'd suggest, have a wide enough gene pool that 'inbreeding' shouldn't be needed, or = problems.   People here will know the KC won't register puppies from true inbreeding in any case now.

Brilliant Dill!  Thanks, that link is useful.  :)

People seem to think that outcrossing is the saviour for all problems, without realising that dogs don't need to be related to carry the same problems!

To me knowing what's behind the dam and sire is the best way to produce healthy puppies - not importing fresh blood without knowing what problems its bring with it. :(

Funny as I was thinking about all of this the other day. We also regularly think about people "if those two were dogs you would never let them breed"!

Never thought the stats for genetic disease in humans would be that high though.

..... and it's a fact that even with prior research, unless two dogs (lines) have been put together previously, mating two lines that have never been used together before, can produce the unexpected!!   At least, however, with a bit of research, especially when importing, the unexpected should be kept to a minimum.   I had all this 'we don't know what's coming in' comment when I brought my hounds back into the UK from Canada - and they originally came from the UK into Canada, where the reaction was somewhat similar.  Experienced breeders know the relevance of phenotype and genotype though.  Interesting to note now, some decades on from then, how successful their use has proven to be, when used by the breeders who were prepared to take the 'risk'.   lol.

Remember, these are just the stats for Mendelian inheritance.   So single genes.   Polygenetic problems would add to the numbers ;-)

There's a lot more info out there on the prevalence of genetic disorders and diseases, but mostly behind paywalls.

The true picture could be a lot worse.

/these figures are also ONLY for the UK.

Of course, considering how mixed the genetic heritage of each of us,   it's also interesting that we each have the potential for 400 genetic diseases!     And 1 in 10 expected to develop a genetic disease !

Pedigree dogs appear to be rather better off than humans!    I

Researchers at Cambridge and Cardiff have found that, on average, a normal healthy person carries approximately 400 potentially damaging DNA variants and two variants known to be associated directly with disease traits. They showed that one in ten people studied is expected to develop a genetic disease as a consequence of carrying these variants.

http://www.sanger.ac.uk/about/press/2012/121206-damaging.html

It's as I always thought,  mating two animals with differing genetic inheritances, simply MULTIPLYS the potential for disease, rather than reduces it.       Strange how supposedly intelligent, scientifically trained people can believe that mxing the breeds could possibly lead to less disease.   This is short term thinking.  At first, there may appear to be a reduction in genetic diseases.   But in the long term, there would be an increase in both the potential for disease and the prevalence.