Our example here tells us that plant breeders developed seedless watermelons by creating polyploid plants. Normally, watermelons, or Citrullus lanatus, are diploid, with 2n=22, but breeders create watermelons that are tetraploid, with 4n=44, by treating plants with a known mutagen that prevents the segregation of chromosomes during mitosis, creating cells with twice as many chromosomes. These plants could then be self-fertilized to create the new tetraploid breed. The plants grown from matings between these tetraploid plants and diploid plants are then sterile and therefore grow no seeds and, well, note they are delicious to eat. Right?
So, if you've ever had a seedless watermelon, which you probably have because that's mostly what they sell nowadays, right, you've been having a hybrid between a tetraploid and a diploid breed of watermelons. Alright. So here it asks, as described, are tetraploid watermelons allopolyploids or autopolyploids? Alright. So what do you think?
Well, let's remember those roots here. 'Allo' means other or different, 'Auto' means self. So, allopolyploids start with hybridization between two species, whereas an autopolyploid just starts with a mutation within one species. And that's what happens here. The species are treated with a mutagen, so we get that mutation. There is no hybridization event that starts this out, so these are autopolyploids.
Regarding the question, "How?" I'm just going to say there was no hybridization to create the polyploids. Alright. Now, diploid and tetraploid watermelons are typically considered the same species. Based on the information above, however, by which species concept could it be reasonable to consider them different species? What do you think? I'm going with that good old biological species concept. Right? These things are clearly reproductively isolated.
They have postzygotic reproductive isolation. Their hybrids are sterile. That meets the biological species concept definition of a different species. Now, we typically call them the same species because people just did this in the lab. It's not something that evolved in nature, and we did it just so that we could have yummy seedless watermelons. But by the biological species concept, this matches the criteria for reproductive isolation, and it's reasonable to call them different species. Alright. For that, more practice after this. I'll see you there.