Alright. Welcome back, and this is the final lecture of week one, The Hybrids. Now just kind of as review, you know, one to bring up again, the, the family of Equidae. And that includes horses, donkeys, and zebras, and so the hybrids is going to be the, the combination of, of two of those. So you can see the general definition of a hybrid, and you know, it's important to, to kind of understand how these come about. So, if I was going to take say a Shire horse and breed it to a thoroughbred both are equus caballus so that's not a hybrid. That's a crossbred. So, that wouldn't be considered what we call hybrid. But, if you took that Shire horse and bred it to a Mammoth Jack donkey which I would really like to see the offspring of, of these matings. So that's Equus caballus and Equus asinus, then you would get a hybrid. So that's two species, distinct species that you're breeding. Now, creating hybrids within Equids is not really that easy. And it's really because a lot of the Equids have a different total number of chromosomes. And so it's worthwhile to just kind of briefly cover what chromosomes are and how they come about you know, forming new organisms. Now the chromosomes are stored in, in the nucleus of almost all cells and that contains all the DNA or genetic material, you know and tells it to do its function or program or develop into a baby horse and, and so on and so forth. Now, during mating half the genetic material comes from mom and half the genetic material comes from dad. They come together and they combine and form you know, offspring or the foal. So, if we took the example of the horse, the mom has in her oocyte or her eggs, has 32 chromosomes. And then dad's cell, the sperm cell that comes in and fertilizes the egg has 32 chromosomes. They combine and the horse is going to have a total of 64 chromosomes per cell. So, so that's important to remember. Now again, when these chromosomes come together, you have one from mom and one from dad. And so they're going to come and combine and match up like this. And then those are, that's chromosome, say that's chromosome one. And then, individual chromosome two from mom, individual chromosome two from dad comes together, fuses, that's chromosome two. Then chromosome three, and so forth. You know, through all of the chromosomes of the horse to where there's 64 total chromosomes. So we can say the horse has 64. Now when we go through the other Equids, say donkeys, they have 62. So you know, and we're going to talk about mules and hinnies here in a second, but when you mate a horse and mate a donkey, the offspring's going to have 63 chromosomes. Which is a mule or a hinny. Now, the three different zebra species actually have different chromosomes. So, it complicates it a little bit more. So, the plain zebra has 44, and then the mountain zebra has 32. And then the Grevy's zebra has 46. So you can see the Mountain zebra has the lowest of any Equid with only 32 chromosomes. So half of what a horse has. So when you're mating these two species with the horse oocyte with 32 chromosomes and the Mountain zebra who has 32 total chromosomes. So when I say that remember half comes from mom half comes from dad. So their egg and sperm have half that number. So 32 so it's 16. So the mountain zebra sperm cell only has 16 chromosomes. It's going to come together, line up with that horse oocyte, line up 16 chromosomes, and then that actually leaves 16 individual chromosomes from the horse with no, no pairing. So, those genes that are there, that are, that, that those genetics are, are in essence, lost. So, that's why a lot of these hybrids fail, because you're not getting proper you know, combination of the genes to produce offspring. Now, we're going to talk about the, the first hybrid is the horse and donkey hybrid, and it results in two types. So if you mate a female horse to a male donkey or a jack, so a mare to a jack, you get a mule. And what's interesting is this, this is pretty successful. So, they get a 90% ferti, fertility rate, you know, really good fertilization rate and reproductive rate. And that's probably why we see so many mules in the world today, over 10 million, is because you made them and, just, just like any other horses, or donkeys, you know they, they have good rates. Now when you do the reverse, and so you do a jenny, or a female donkey to a stallion, or a male horse, we don't see the same results. And this is called a hinny. And they actually have fertilization rates or fertility rates less than 15%. So, that's why they're a lot more rare. So, you know, in science, at, as scientists, we have not really found the reason why. You know, we've looked in the literature, and there's really no reason why this doesn't work as well as the reverse, making mules. Now, it's also remember, important to remember that their offspring are going to have 63 total chromosomes. So you got 64 from the horse, 62, 62 from the donkey. You know, you bring those together, you're going to get 63 and they're going to be sterile. So that's why you don't see mules breeding, because they're sterile. Now horse and zebra hybrids have, have been successful, and they have actually been successful across all three zebra species, which is really interesting. So, it is possible, but, you know, their fertility rates aren't, aren't as great, as you'll see. These are actually called Zorses or Zebroids. Now Zebroids can mean you know, as we'll see in a second, the horse and donkey hybrids. But I like to just think of Zorses. I think its a, its a cool name and, and every time I see pictures of these I'm always amazed you know, that, that they were successful doing that. And again their fertility is greatly reduced because the mixing of those chromosomes doesn't always result in, in offspring. Now, donkey and zebra hybrids, those are possible too. And again, they're known as Zebroids, but, or, you can call them Zonkeys which again, is a kind of a cool name. So, you know call them a Zonkey. And their fertility again is greatly reduced. The mixing of those chromosomes doesn't always work right, so you know, it, it's kind of a, somewhat more rare occurrence than breeding two of the same species. So, this brings us to the end of week one. And, you know, thank you for, for taking the time to watch all the lectures. Just a quick reminder, take quiz one and for next week, we're going to start jumping into physiology. We're going to start talking a little bit about coat colors, some more, some more terminology, and then jump into hoof care and then kind of develop you know, a hoof care plan, and I look forward to seeing you then.
