00:01
Hello students, in this question we have been asked to give the complete genetic explanation for the following case.
00:11
So the scenario is that in a pair of identical twins, one is normal and the other has down syndrome.
00:28
So what has happened here? so to first understand down syndrome is caused by the trisomy of chromosome 21.
00:39
Now trisomy can be either the whole part of the chromosome being here or even a certain half of it can be called trisomy.
00:59
So now let us understand what happens in case of identical twins.
01:05
So now this is my zygote, the normally fertilized zygote with one ovum getting fertilized with one sperm.
01:17
Now this is growing and as this is, as this embryo is growing suddenly there is a break and this particular group of cells get divided into parts.
01:38
Now both of these parts will grow into individual offsprings.
01:43
Now this is what happens in case of identical twins.
01:47
They are identical because they come from the same genetic material because both the mother's and the father's genetic material is same in case of both of these groups.
02:03
So this is how you get a identical twin...