00:01
Okay, i want to answer this question, we have to talk about myosis.
00:03
It says a person has a total of 46 chromosomes.
00:07
So normally remember that a person is diploid.
00:10
Okay, this is diploid and this is one pair of homologous chromosomes, for example.
00:16
Okay? but in this case, it says that this person has a total of 46 chromosomes.
00:21
In humans, as i said, this is normal that diploid number is 46, but in this case, this person has, or well, let's do this.
00:32
Remember that your chromosomes, if they are not going to undergo cell replication or cell division, they are going to be like this.
00:39
For example, this is one pair of monologous chromosomes, and this is going to be another pair of monologous chromosomes.
00:45
So you have pairs, in this case, as you have 46 chromosomes, you have 23 pairs because 23 multiplied by 2 is 46.
00:52
So it says that this person has 46 chromosomes where one is normal.
00:59
It means a normal chromosome number 14, and abnormal 14 fuse with 3.
01:04
21, so this is going to be 14 with 21, plus 22 normal pairs of other chromosomes.
01:13
So you're going to have many chromosomes here, and one of them are going to be 22 chromosomes.
01:19
Okay? well, what has happened here is the process of goversonian class location.
01:25
Remember that, for example, when you have this is your chromosome number 14 and this is your chromosome number 21, i suppose this is one pair of chromosome 21, and this is one pair of chromosome 14.
01:37
What happens, practically in robert's sondran trach location is that, for example, this chromosome here is going to lose this segment and the same for this chromosome 14, and they are going to fuse these like long arms of the chromosome.
01:53
And you're going to have that this part is going to be the long arm of chromosome 14, and this is going to be the long arm of the chromosome 21.
02:02
Okay, but even when you have only the long arms, they are going to count as one chromosome.
02:08
Okay, for example, this is going to count as one chromosome 11 and as one chromosome 21.
02:17
So you have practically 22, 22 pairs, going to the equation, you have 22 pairs here, and here this is another pair.
02:28
This is one pair where you have one single, one normal, 14, chromosome 14, and one abnormal one, chromosome 14 with chromosome 21.
02:37
So it says that a plus 22 normal pair of other chromosomes, including chromosome normal pair of 21.
02:46
So besides you have here an extra 21, you have two more chromosomes 21 because you have one pair for chromosome 21.
02:53
So you can see like this is one pair for chromosome 14 and well you have all the other chromosomes or chromosome pairs here.
03:04
Including chromosome 21.
03:05
Okay.
03:06
So it says which are the following statement is correct to this person.
03:12
Option a says genotypically and phenotypically abnormal as familial down syndrome due to extra copy, due to extra copy of 14.
03:21
And this option is false.
03:24
Remember that down syndrome can be like there are there are practically three types of down syndrome, okay? one is the famous that you know that is 21 or practically 3 -721 where you have 3 chromosomes 21, this is 1, this is 2, and this is 3.
03:42
So you have three copies of chromosome 21, this is 3 -7 -21.
03:46
The second is when you have a goversonian translocation.
03:51
In this case, for example, you can have your normal pair of chromosome 21, but you're going to have that one of your chromosomes, of your chromosome number 14, is going to have one arm with a chromosome 14 and the second arm with, that is like, from a chromosome 21 here.
04:10
So you have one, two and three chromosomes 21.
04:13
So this is going to be also down syndrome.
04:16
And this is important because this is not familial.
04:19
Okay, this is because of probabilities because a process called non -nist unisonation that occurs in myosis.
04:24
But in this case, goversonian translocation, when you have a down syndrome with, because of goversone and translocation, this can be familiar.
04:30
It means you can transmit down syndrome to other people, including you can be a carrier or down syndrome if you have this problem here.
04:40
And the third case is when you have mosaicin.
04:44
Okay, most of the season is when you, for example, have a normal cygote because of fertilization and this is going to be 4n, i'm sorry, a 2n diploid.
04:56
But during mitosis, there is going to be a non -disjunion and some cells are going to receive three copies of the chromosome 21, okay, three copies, and the other one is not going to receive it's going to be normal...