Ok guys, now let's discuss about genomic imprinting. See what is the concept of imprinting, genomic imprinting? See, first let's discuss what is normal sir. Ok, now imagine there is chromosome. Ok, there is a chromosome.
For example, chromosome number 10, 11 or something. For example, this is chromosome number 1, this is also chromosome number 1. So, In each and every cell you have two chromosomes okay, one chromosome from mother, one chromosome from father okay. This number one chromosome you will get it from mother as well as from the father okay. So same chromosomes okay. Here there is a gene for example there is a gene for color and the same locus here also there is a gene for the color okay.
Here is a gene for the color, here is a gene for the color. So the same locus same genes are there. Now for example Mother is coding for light colored skin. Father is coding for the dark colored skin.
Okay. See, both are functional. Both are active. Whatever the gene is dominant or I should say whatever the allele that is dominant.
Here the gene is for the color. There are two alleles. Light color allele, dark color allele. So, whatever the allele that is dominant, only that allele will be expressed. Okay.
So, the boy is going to be either dark or fair according to the which allel is dominant. Most of the time, black. Okay. Black allel is dominant.
That's what I am saying. So, this is what Mendel said. Two allels will be there. Whatever is dominant, it will be expressed. That phenotype will be expressed.
But, what is genomic imprinting is, yes, there are two allels, but certain allels are absolutely silenced. There is something called as silencing, gene silencing because of the process of methylation. For easy understanding purpose, let me show you the chromosome number 15. Okay, this is chromosome number 15 from mother, the same chromosome number 15 from father. Okay, this is chromosome 15, this is also chromosome 15. Now, on the chromosome number 15, for example, in this area I am showing.
Now, here The allel is present, here the allel is present. But this gene, whatever I'm saying, this gene is called as a snorp gene. Okay, snorp gene.
This snorp gene in the mother is always silenced because of the process of methylation. Always this gene on the mother's chromosome, maternal chromosome is always silenced. It is not going to be expressed. Who is going to be expressed?
Only, only The paternal snorp genes are expressed. It's a paternal snorp genes are expressed. This is not something given by the Mendel.
Mendel said two Ls will be there. Ok, same gene two Ls will be there. Whatever it is dominant it will be expressed. Here also same thing.
The gene is snorp gene. So, allele which is present and the mother is always silent and this snorp gene is only only expressed from the paternal gene. So, it is silenced because of the methylation process that is silenced.
Acetylation is going to activate the genes. Methylation is going to inhibit. So, silencing in the same way again I'm talking about different set of genes now different type of genes and the same chromosome number 15 look this is 15 from the mother 15 from the father ok maternal and this is paternal now there is one more gene which is called as a UBE 3a, UBE 3a gene.
Now, this gene is also present on the father as well as the mother, okay. Maternal, paternal, it is there. But look, the paternal, okay, the paternal is silenced now because of methylation. Because of the methylation process, okay, this side I have it written it like this, right, okay. Let me follow the code.
See, it is male, female. So now look, this UBE3A gene, where it is silenced, a UBE3A gene is silenced in the father because of methylation, silenced. So now tell me, UBE3A gene is only only expressed in the mother but snorp gene is only only expressed in the father.
Now we will discuss about two diseases. Ok, the first disease that I'm going to discuss which will occur because of the genomic imprinting, it is called as, see whatever I have discussed now, this is so far it is absolutely physiological, this is physiological. I'm going to discuss about the diseases.
What are they? The first disease is called as the Prader-Welle syndrome. So, what is the problem with the Prader-Welle syndrome? See in Prader-Welle syndrome, Look, the snorp genes are only only expressed in the father. Ok, only in the father the snorp genes are going to be expressed.
They are only function in the father. What happens if you lose this chromosome? If you lose this chromosome, you lost. That chromosome is deleted. So deletion of paternal 15. Ok, so write deletion of paternal 15. 15 chromosome number 15 Especially PR here.
I am showing out on the Q arm, but it's a PR. Okay paternal 15 be lost So deletion of paternal 15 now tell me imagine there is this person in him The snorkeling's are only only active in the paternal chromosomes that paternal chromosome he lost now He is having maternal chromosome, but it is non-functional. It is silenced.
So he is going to manifest the disease So those genes which are only only active on the paternal chromosomes are lost The maternal genes are there but they are silenced. So, this condition is going to cause the Prader-Willi syndrome. See, this is the one reason for the Prader-Willi syndrome. Most of the time, this will show up in your exam. Especially for the competitive exams like NEET-PG exams.
Now, one more thing you have to know. See, in Prader-Willi syndrome, what is the other condition which can lead to the Prader-Willi syndrome, other cause for the Prader-Willi syndrome is maternal disomy. ok maternal disomy 15 maternal disomy 15 what does that mean by see in each and every cell ok in each and every cell we have two chromosomes 15, 15 chromosomes from father 15 chromosomes from mother one should be coming from father one should be coming from mother what if during the gametogenesis process during fertilization process what happened is now this baby he got two 15 number chromosomes ok two 15 number chromosomes only from the mother This is called as a maternal disomy 15. One should be coming from father, one should be coming from the mother.
But now what's happening here? The two maternal chromosomes are coming. Two 15 number chromosomes are coming from the mother.
This is called as a maternal disomy of chromosome number 15. So that will also cause Prader-Willi obviously, no doubt. Because there is no 15th chromosome. 15th chromosome is not there from the father. So no active genes. Prader-Willi syndrome will occur.
Okay, in the same way, the next disease that I want to discuss here is called as Angelman Syndrome. So, it's very simple. How I used to remember is, angel is like mom, mom is like an angel. Prader-Willi, paternal, Prader-Willi, paternal 15 deletion, Prader-Willi, paternal 15 deletion, something related to the father, the father related genes are gone.
Paternal 15, lemur chromosome is lost. Angel, angel is the mother. Okay. So, what happens in Angelman syndrome is, see I have explained you here UBE3A gene. UBE3A gene is only only functional in mother.
Look, it is only only functional in mother. Now, what if you lose this maternal chromosome number 15? So, deletion of maternal 15. Okay. So, write deletion of maternal chromosome number 15. Gone.
It is gone. So, it can lead to the Angelman syndrome. One more possibility is there.
By this time, you should like at least think about it. Sir, you will get chromosome number 15 from mother, one from father, one from mother, one from father. What if you get it both from the father? The sperm is bringing two 15 number chromosomes. You are getting both the chromosome from father itself.
Okay. So, that is paternal disomy 15. paternal disomy 15 both 15 number chromosomes are coming from the father if you get both the chromosomes from the father see father ub3a genes are already silenced so active genes are not there so active ub3a genes are not there no transcription no translation so proteins are not going to be formed so that will lead to which condition angelman syndrome angelman syndrome now this baby look this baby is having angel sorry prader-willi syndrome this fellow is having the prader-willi syndrome so in prader-willi syndrome let me write the clinical features Okay, Prader-Willi fellow, he is having which clinical features? First of all, look, he is having obesity.
He is obese. So, he is going to have short stature, obesity. He's going to eat more, hyperphasia, ok, hyperphasia is going to be seen.
If you look at his muscles, there will be hypotonia, he's going to have hypopigmentation, ok, hypopigmentation. He's going to have a very low impulse control, he cannot resist himself from doing the things, low impulse control. Low impulse control. So, low impulse control, he will be eating, eating, so that he will be obese. So, this is the Prader-Wallace syndrome.
Prader-Wallace, paternal. Paternal, 15 loss or maternal disomy, 15. Prader-Wallace. Simple.
Which genes? Snorp genes. Snorp genes are silenced in the mother, they are only active in the father.
Next, the syndrome that which I want to discuss is the Angelman syndrome. Already you know the etiology. Angel is a mother. Maternal, 15 loss or paternal disomy, 15. Now, the important point, see, if a...
Person is having this Angelman syndrome see always this patients are having this characteristic weird smile is there So they are just like a laughing dolls are these people are called as a happy puppets They are looking like a dolls which are always laughing so they're happy puppets So, what else will be seen? Seen angelments. See, the smile is there.
Happy puppets. These patients are going to have the seizures. Intellectual disability is going to be seen. Okay. Wide spaced tooth.
The tooth are going to be wide spaced with the seizures. Intellectual mental disability. That happy face. All these things are going to be seen. Okay.
So, with this, we have completed the topic of genomic imprinting. The two important disorders which will be involved in the genomic imprinting is Prader-Willi as well as angelments. Hope the video is helpful.
Thank you.