00:04
Let's answer this question.
00:05
Let's talk about cell division, okay? so this question says, question a, if a cell has a diploid number of eight, so you have here a different number of eight, before myiosis, how many chromosomes will be in each of the four cells after myosis one, myosis two, if one pair of homologous chromosomes, experiences, non -disjunction in myosis one.
00:25
So first, let's draw that normal myosis.
00:27
After myosis one, you produce two cells that are haploid like this.
00:32
And after myiosis 2, you produce more haploid cells from each of these daughter cells.
00:41
And these are your four daughter cells after myiosis 2.
00:45
So what happens if another huge occurs in myiosis 1? so let's use here, for example, the heterocygose a.
00:56
Let's suppose that this is a genotype for this, okay? the heterocygous a goes a.
01:00
So during myiosis 1, what happens is that the dominant a goes here and the decisive a goes here, and you have this.
01:07
Then during myiosis 2, you copy each of these allele's, and you get two a's, two dominant a's, and one goes here and the second goes here.
01:15
So you get here, dominant a, dominant a, and the same here, excessive a and the sle.
01:19
So during a non -disjunction in myosis 1, this is what happens.
01:23
You get the heterocybo's, but instead of moving the dominant a to one cell and the decisive a to the second cell, both move together like this.
01:32
And this gets a heterocybolysis a.
01:35
It means instead of having four chromosomes, it has gained one chromosome extra.
01:42
So it is going to be n plus 1 or 5.
01:46
Then myosis 2 occurs and you're going to have here heterocygous a, heterocygous a, and here you get 0 and 0.
01:53
It's a myosis 2.
01:54
So the question says, how many chromosomes will be in each of the $4 cells after a meiosis 2? so if a nonetheless you're going to have here five chromosomes, five chromosomes.
02:09
You're going to have here three chromosomes and three chromosomes because it has happened only for one pair of chromosomes, not for all the chromosomes, okay? so you have lost one chromosome here, one chromosome here, and here you have gained one chromosome.
02:22
The next question says if a diploid parent cell has four chromosomes, so this is your diploid parent cells has four chromosomes, this is one chromosome, it is homologous chromosome.
02:41
And this is the second pair, your four chromosomes, okay? and show how the chromosomes align at the metaphase plate during mitosis, myiosis 1 and myiosis 2.
02:54
So during mitosis, this is your spindle, okay, your chromosomes are going to align like one in each.
03:07
It means like this.
03:09
One black chromosome here, another black chromosome here, and the same for the blue chromosome.
03:22
Like this, okay? you have this.
03:45
Okay, so this is how your chromosomes are going to align in mitosis.
03:50
It says include the kinetochore microtubules.
03:53
The kinetochorbidubules are these microtubules that are attached into the middle of the chromosomes.
03:58
Okay.
03:59
And the centrosomes are found here.
04:06
Okay.
04:08
Now, what happens in meiosis 1? in myiosis 1, this is different because your chromosomes are not going to align like this, but they are going to align in pairs.
04:17
So you have here this, and here you have this, okay? so you have your kinetocor microtubules, and you center chromosomes here...