What is a beagle, really?
July 23, 2015 7:09 AM   Subscribe

Say you have two pure-bred dogs: a pug and a beagle. If you breed them, you will end up with a crossbreed of two purebreds: a puggle. Is it possible to breed two true puggles and end up with a dog that is by breed standards (or genetic standards?) identical to a pure-bred pug or beagle? Thank you.
posted by griphus to Pets & Animals (12 answers total) 3 users marked this as a favorite
I mean, I'm no Barbara McClintock or anything, but wouldn't you end up with a third puggle?
posted by Juliet Banana at 7:16 AM on July 23, 2015 [2 favorites]

"Possible", yes, technically. But vanishingly unlikely.

If you have a bowl of M&Ms and a bowl of Skittles, and you dump half of each bowl into a 3rd bowl, you get a mixed bowl. If you take two mixed bowls, and dump half of each into another bowl, you could theoretically end up with all Skittles in that bowl, but realistically you'll end up with a reasonably balanced mix. Maybe one time you end up with more Skittles, maybe one time you end up with more M&Ms.

I'm hungry. What were we talking about?
posted by jeffjon at 7:20 AM on July 23, 2015 [62 favorites]

Not in a single generation. Because inheritance is particulate, you can recover individual parental characters from an F1 cross (that is your puggle x puggle mating in your scenario). It would be very unlikely to recover all characters though. It's essentially like asking if a grandchild can have no genes from its grandfather and only genes from its grandmother.
posted by cnanderson at 7:22 AM on July 23, 2015 [2 favorites]

You could end up with anything from a pure-bred pug to a pure-bred beagle. But it would be a very very small chance of getting all one or all the other.

Imagine a really simple case of breeding a white dog with a black dog to get a gray dog. If there's only one gene for coat color (there are in fact several), if you bred two of those gray dogs you would (on average) get 1/4 white dogs, 1/4 black dogs, and 1/2 gray dogs. If there are two genes that impact coat color, you would get 1/16 white dogs and 1/16 black dogs and the rest various shades of gray. Three genes -> 1/64

There are probably hundreds of genes that contribute to "pug" ness vs. "beagle" ness, so the chance of getting a "pug" or "beagle" from a simple puggle cross is exponentially tiny.
posted by mskyle at 7:22 AM on July 23, 2015

The first answer on this Yahoo question seems to check out with a little googling. It looks like the search terms you're looking for are "f2 generation" and "designer dogs."
They're not as predictable as a purebred dog, but F1 and F2 generation hybrids will show a selection or combination of characteristics found in the original purebred dogs that founded the new 'breed'.

- source
posted by Juliet Banana at 7:23 AM on July 23, 2015

Sure, it's possible that everything could line up perfectly in the phenotypic crapshoot of breeding (just like it would be possible for a brother and a sister to have a kid that looked exactly like one of their parents), just phenomenally unlikely. If I remember from genetics class, for humans it's something like a 1 in 4 trillion chance.
posted by phunniemee at 7:23 AM on July 23, 2015

You could not end up with a purebred pug or beagle by breeding two puggles, because the very definition of "purebred" is that it is the offspring of two dogs of the same breed. Whether or not the offspring of two puggles would effectively be a pug, a beagle or simply another puggle is a more difficult question. It's extremely unlikely that you would end up with anything that conformed to the breed standards for pugs or beagles. At the same time, it's extremely unlikely you would end up with another puggle. Creating a dog breed is more complicated than that. Part of the deal with a dog breed is that the offspring of two purebred dogs will always have the same constellation of breed standards in physiology and temperament. It's possible that many generations of careful breeding could produce a new breed of puggles that would breed true, but certainly not in one generation. So, whereas breeding two pugs together will produce a litter where all the dogs look more or less the same, breeding two puggles together would be likely to produce a litter where all the dogs look pretty different.
posted by slkinsey at 7:27 AM on July 23, 2015 [6 favorites]

By genetic standards, yes, it's possible to get pretty close, but unlikely to be 100% because of mixing at the chromosome level. The term for this is an F2 cross. An example in humans (not to be too weird) are the cases you see in the news sometimes about human twins from an interracial marriage where one twin is very pale and the other is dark skinned, like here
. Their father is white and their mother is half Jamaican. Most of their kids show a mix of characteristics but one is a pale redhead. The pale child happened to get most of her mother's European ancestry DNA for outward appearance characteristics.

I don't think breeder standards would ever buy this though.
posted by permiechickie at 7:28 AM on July 23, 2015

Wouldn't it more or less have to do with the number of chromosomes? Leaving aside things like genetic material getting clipped off one chromosome and attached to another, the possibility should be small but calcuable if you know how many chromosomes dogs have and are able to do a bit of math that this humanities major is not willing to work out on his phone. (1/2)^n maybe where n is the number of chromosomes?
posted by tivalasvegas at 7:33 AM on July 23, 2015

Leaving aside things like genetic material getting clipped off one chromosome and attached to another

Except you can't really do this - cross-over events are actually fairly common. It turns out you can map the location of genes on chromosomes due to the frequency of cross-over events. How this was figured out is one of my favorite stories in biology. Basically, an undergraduate at Columbia blew off his homework to work on some puzzling data from breeding records.
posted by cnanderson at 7:46 AM on July 23, 2015

tivalasvegas almost has it, except it's not number of chromosomes, it's number of genes. Specifically the number of genes which differ between beagles and pugs, so not the "generic dog genes".

Which is its own problem... is a "large pug" gene the same as a "small beagle" gene? Or is it a "generic smallish dog" gene?
posted by mskyle at 7:46 AM on July 23, 2015 [2 favorites]

Some traits are patrilineal and some are matrilineal. So, for example, if both grandmothers are pugs it might be impossible (not just vanishingly unlikely) to ever get a pure beagle back.
posted by alms at 9:02 AM on July 23, 2015 [2 favorites]

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