This example tells us that around the world, people have bred domestic cattle or Bos taurus with other local related species. In Nepal, it is common to breed cattle with domestic yaks or Bos grunniens. The offspring, called Zho, are usually larger and stronger than either parent species and contain desirable traits from both. Male Zho are usually sterile, but the females are fertile. Nevertheless, the females are seldom bred because the second generation hybrids tend to be smaller and weaker compared to both yaks and domestic cattle.

Alright, with that information, we need to answer these questions. A says, based on this description, should yaks and domestic cattle be considered different species? Yes or no? What do you think?

Well, I'm going to go with yes. Alright. I definitely see forms of reproductive isolation between these two species. So knowing that, let's move on to B. B asks if yes, is the barrier prezygotic or postzygotic?

As described in this passage, I see postzygotic barriers. Right? There may be prezygotic barriers between these two groups, but here we have mated them. Now what happens? So, we have made hybrids. So now we are looking at those postzygotic barriers. The question here for C then is if a pre or postzygotic barrier is present, specifically what type of pre or postzygotic barrier is it.

If more than one type is described, list all types of barriers. Alright. So what do you see? Well, I see the males are sterile, which is a form of hybrid sterility. Alright. But is that it though? What I also see is that the females, well, they are usually fertile, but they are seldom bred because the second generation hybrids tend to be smaller and weaker. Well, that sounds like hybrid breakdown.

So, we see two forms of postzygotic barriers here: hybrid sterility and second generation hybrid breakdown. With that, more practice after this. Give it a try.