In humans, identical twins are possible because a. extraembryonic cells interact with the zygote nucleus. b. convergent extension occurs. c. early blastomeres can form a complete embryo if isolated. d. the gray crescent divides the dorsal-ventral axis into new cells.

Video transcript

Welcome back now. We'll look at the question in humans. Early blast Amir's can form a complete embryo. If isolated, this becomes the basis for the formation of a fraternal twins. Be identical twins. See conjoined twins or D. All of these. So we do have the possibility of all answers being correct. Well as we recall from condom videos, the blast Amir comes in very early development. We start with the zygote. When egg meets sperm and fertilization, that zygote in the very beginning begins to divide. In my talk series of my topic divisions that gives us identical daughter cells. We have a multi cellular blast Amir at this very early stage. What's important to note about the blast Amir? So this is multi cellular and the cells are all identical to each other. In this stage nothing has been begun to differentiate. And they are all toady potent meaning every cell in the blast of mirror has the potential to become any type of cell in the body and can go on to develop a fully functioning fertile adult organism. So when we isolate any cell from the blast Amir because it is totally potent, it can go on to develop a separate individual organism. And these organisms, any organism developed from this would be identical. They have the same D. N. A. So looking back at our choices, the first choices fraternal twins or fraternal twins form when you have to separate eggs fertilized by separate sperm. That's not what we have here. So we can eliminate choice A. As soon as we eliminate one choice we know we can eliminate choice D. Since we know not all are correct. Choice B. Is identical twins. And indeed we have here. We know that any individual that develops from blast amir cells from the same blast. Amir will have an identical genome. So that is the basis of identical twins. Choice C. Is conjoined twins, conjoined twins. Or when you have an early embryo that starts to separate at this boston stage and has an incomplete separation. So Choice C. Is not our answer here. So our answer is again be identical twins. Thanks for watching. See you in the next video.