Genetics 101

[Wally 'n' Leto]

For those who would like to know more about genetics, here's a simple explanation.

If you breed an animal with a high risk of a certain anomaly with another animal with at high risk of the same anomaly, the offspring will be at high risk of the anomaly, no matter whether the parents are the same or different breeds. The exact odds of the offspring having the problem depend on the mechanism of heredity (eg recessive or dominant or multifactorial). You can reduce (or increase) the odds of offspring carrying certain traits by careful selection of matings, but in the end it all comes down to a roll of the dice.

Hybrid vigour only applies to an animal with a risk of an anomaly being bred to an animal without the risk of the anomaly. Like a dog with stenotic nares being bred to a dog who does not carry that trait - then you REDUCE but not eliminate the risk of the offspring having the trait. You can still get unlucky and have the offspring carry the undesired trait. For example, breeding a pug to a cavalier and expecting to lower the risk of bulging eyes, stenotic nares, long palate and bad kneecaps does NOT MAKE SENSE.

Line breeding and inbreeding within a breed not only increase the odds of offspring carrying desirable traits (which is why it is done), it also increases the odds of undesirable traits that are carried in a family line. Mating 2 unrelated animals of the same breed with an undesirable trait (say 2 pugs with stenotic nares) will more likely give you a pup with stenotic nares than if you bred one with open and one with stenotic nares.

ANY breeding animal, of any species and any breed, should be shown to be free of heritable faults whether it's through genetic testing or physical exam. And an animal should only be bred to another animal that reduces the chance of having these undesirable traits, whether the mating be within breed or across breeds.

The saying in the horse racing world is "Breed the best to the best, and hope for the best." Really, all animals (you can include people in there if you want) should be bred to the same philosophical standard.

[Wonka & Nilla]

Well written - thanks for the genetics lesson!

[lotusseeds]

Thank you for your genetics 101 lesson.
Questions,
just tossing these out there with no agenda, I hope this does not stir up more "drama".
In my reading I have come accross literature on Brussels Griffons and have read about the crosses that were done with pugs to create a smooth haired BG and it also created a stronger dog that we see today. Are there other examples of crosses that have been positive in the past? I know today it is all about the money, but in the past, weren't breeders selectively breeding crosses to increase the robustness of the animial?
Are there any examples of crosses that when done with genetic screening are acceptable? Also do the breeders just breed for that generation, the F1 and require that the buyer sterilizes the F1 dog so that there are no F2's? or is it laissez-faire without caring what the new owner does?

[6 Beautiful Pugs]

Developers of breeds have brought in outside blood to improve a breed with genetic weaknesses or to introduce a desirable trait. The desirable trait does not always have to improve the health, dogs and dog breeds have been molded for function and for fashion for thousands of years. This is where controversy can occur.

Look at the number of breeds of horses, dogs and cats which are offshoots of other older breeds. Look at the size ranges of poodles and schnauzers. Paint horses are pinto Quarter horses, a color pattern not allowed in the original AQHA registry.

Then there are the crosses between horse and donkey (mules). Sometimes the mule will inherit the best of both parents, sometimes the worst, but most times the progeny will exhibit a blend of both the good and bad traits of both.

Ever since wolves, wild horses and cattle and wild cats began to live with man, man has bred them and altered them to his pleasing. There is no reason to think that the curiosity that drives man to see what would happen if we mixed A with B will ever end. The number of recognized breeds (both utility and companion) will continue to increase. There will be cross-breeding, linebreeding and inbreeding and these will give both desired results and undesirable results.I know in horses, you can breed an Arabian and a Thoroughbred together, resulting in a Anglo-Arab, but I believe the results are less predictable if you were to breed two Anglo-Arabs together. I think that would apply. I am also thinking of the history of the POA (Pony of America) and Morgan horse.

"The first Pony of Americas was introduced in the year 1954. That was when Leslie Boomhower, a breeder of Shetland ponies from Iowa founded the breed. Included in Pony of the America’s development are the American Quarter Horse, Wild Mustang, Thoroughbred, Welsh Pony and the Arabian. He founded the Pony of Americas Club in 1956."

"The Morgan is the first documented American breed and the founding sire was born at West Springfield in Massachusetts. Over the years, it's been a major influence on American horse development. The Morgan bloodline has shaped a number of breeds including the Saddlebred, Standardbred, Tennessee Walking Horse, and the Canadian.
The story behind the Morganfounding is truly American. The breed owes its existence to one stallion, a little bay horse named Justin Morgan. Neither big nor remarkable, Justin Morgan was given as a debt payment to his namesake, Justin Morgan, in 1795. After Justin Sr. died, the horse bounced from owner to owner. It wasn't until one keeper, Mr. Robert Evans, discovered Justin's ability when he finally took off. Evans figured out that Justin Morgan could out-haul and out-run any horse in the area. He may have been tiny, but he was fast and strong.
From then on, Justin Morgan was raced in saddle and under harness but also worked hard and put in numerous hauling contests. He was never beat. As a result, he became a high-demand sire and all modern-day Morgans can trace their roots to his three famous sons – Sherman, Woodbury, and Bullrush."

I'm sure back in their day people shook their heads and clucked about these men breeding "mutt" horses.

Then there are the breeds bred purely for unusual looks or features, the Chinese Crested, the Miniature Horse, fainting goats, ragdoll cats, hairless cats...certainly most of the toy group of dogs. Flat faced breeds were bred, not because of the function or with an eye to improve the health of these dogs, but because humans liked the face which more resembled a human baby. It was "cute".

Man strives to be the master of his world and mold the domesticated plants and animals to suit his needs, desires and fancys and as long as man feels this need we will have puggles, chugs, labradoodles, cockapoos, and new breeds emerging all the time.

Take care,
Lisa

[lotusseeds]

Thank you for the Equus spin on genetics and breeding.

[Wally 'n' Leto]

Actually, I have heard that Justin Morgan's horse was probably a Canadian (why he was thought to be small and poorly conformed), or maybe that's just a Canadian desire to have had an uncredited influence in one of the US's favourite breeds. :)

Please someone correct me if Im wrong, but I believe that new breeds, such as the Bengal cat and the labradoodle and goldendoodle, have to be F4 or higher before they are considered to be representatives of a new 'breed'. It takes that long for the characteristics of cross breeding to stabilize and for all the members of the group to start having the same 'look' and personality. Of course before the breed is recognized by a kennel club it must be in existence with a stud book for a certain length of time (I want to say 50 years but I'm not sure).

For those who don't know, I'll explain this F thing, using my own pug shih tzu cross as an example because I have photos to illustrate.

When you take a purebred pug and a purebred shih tzu and breed them....



PLUS




the litter is designated as F1. The result of this coupling is totally random and inconsistent. For example:



and



and



Notice the difference in coat length, coat texture, and relative expression of shih tzu and pug traits. There's no way anyone would say that these 3 are the same 'breed', but they are.

When you breed two F1 dogs, you get an F2 litter.
When you breed two F2s, you get an F3.
and so on.....

If you take an F1 and breed it to a purebred, you get what is called an F1b (b is for backcross)
If you take an F2 and breed it to a F1b, you get an F2b
and so on....


So let's call pug A and shih tzu B

A+B = F1 50% A and 50% B but nobody knows what they will look like!
F1+F1 = F2 still 50% A and 50% B
F2+F2 = F3 still 50% A and 50% B but the traits will continue to stabilize over the generations.

If I want a pugzu that looks more like a pug I could do this:
F1 + A = F1b 75% A and 25% B
Or this:
F1 + F1b (backcross to A) = 62.5% A and 38.5% B

This way, a breeder can titrate the amount of influence from each breed, and shape to the look or performance he really wants.

Let's say I liked pugs and wanted to change a single feature, like say give them a touch longer muzzle, like a shih tzu has. I could try doing this....

F1b + A = 87.5% A and 12.5% B

and then

A+ pup from above = 93.75% A and 6.25% B

But in addition to the longer muzzle I would get other shih tzu traits, like maybe... a brindle coat? long hair? on a dog that otherwise looks like a pug? Who knows! And maybe with that last backcross I would lose that longer muzzle.....

Once I got the look I wanted, I would breed 2 dogs that looked the way I liked, and that would be the F1 superpugzu..... and so on

It's all a roll of the dice, and that's what makes genetics so interesting.

[Wally 'n' Leto]

Just thought of something I should add....

Say I have 2 pugs that I'm going to breed, let's call them A and B again.

When I breed them, I'll get pug AB, who is 50% A and 50% B

But I really like the way pug B looks with his extra white smile, and that didn't really come out that strongly in AB, so I could breed my AB dog back to B, which would make the resulting puppy 25% A and 75% B. Hopefully I'd get that white smile. This is inbreeding: when you breed back to a parent.

Linebreeding is when you breed back to a more remote ancestor, say a grandparent or great-grandparent. Linebreeding has less risk of introducing negative traits, but also less chance of bringing in the trait you actually want because of the diluting effect of other grandparents on the genetic makeup of the younger mate. Figuring out the percentages of linebreeding is something I have never figured out (especially if you have the same grandparent on both parents' sides), but that's the general principle.

[Pugpillow]

Great explanations. One of my concerns is that some supposedly responsible breeders concentrate entirely on conformation (looks) to the detriment of health. This has become a huge issue in European showing and starting to become an issue in North America. Even our beloved pugs have been affected with the concentration on smushy face snout which makes the respiratory function more compromised.

[frankoliverlucy]

This is all great information!
Thanks for the wonderful thread......