00:03
So this question is about sickle cell anemia.
00:06
This is caused by a point mutation in beta -globin gene.
00:10
So beta -globin gene has originally a nucleotide a, and then in the mutant allele, the a become a t.
00:23
So as a result, when the gene is being transcribed into mrn and then translating to proteins that change the codon from g -a -g to gu -g.
00:33
Which caused an amino acid change in their protein from glutamate to valine amino acid.
00:40
So the question also gave you the cutting side of a restriction enzyme called mst1.
00:47
So you can see the cutting side are somewhat different in wild type and mutant alleles.
00:53
The enzyme cut the normal allele three times, which produced two fragments, but it only cut the mutant allele twice, which produced only one fragment.
01:03
So the question asks you to figure out how you can decide the genotype of a newborn who has a show symptom yet, and also it wants you to describe the result of the three possible genotype.
01:17
So first of all, on a board, i draw the two allule.
01:21
One is mutant on the top, the bottom is wild type.
01:25
And we call the wild type capital m because it's a dominant allele, and mutant lower m because it's a recessive.
01:33
Trait.
01:35
So the arrow represent the mst2 cut.
01:39
So you can see in wild type allele, it cut the dna fragment three times.
01:43
One of the cutting site is where the gag is.
01:48
This is original a.
01:50
Now in the mutant, due to the change of nucleotide, a become a t so that mst1 no longer recognize the original site.
02:01
So this site is gone.
02:03
So i put a cross up there.
02:05
So remember, restriction enzyme is super specific.
02:10
If you change the nucleotized sequence of the restriction site, the enzyme can no longer recognize the dna and it will not cut the dna anymore.
02:19
Okay, now we know that the restriction digestion pattern of the two will be different.
02:24
So let's take a look at three different possible genotypes and what we expect for each one.
02:29
The first one is the one that has two homozygars.
02:33
Dominant allele.
02:34
So both are capital m.
02:36
So you can see i put both all the allule on a board for you and both all got cut three times one, two, and three.
02:45
So as you can see after cutting one of the fragment is going to be a and then the other fragment we call it b.
02:57
So you can see both allele will cut, it will be cut twice, three times and produce two fragment.
03:04
One is called a and the other is called b.
03:08
Okay, what if we have a heterozygous genotype, capital m and lower m? so in this case, i put it, again, both allude on a board.
03:16
The top one is a capital m because it cuts three times, and the bottom is a lower m recessive because it only cuts twice.
03:24
Now there is a slight difference.
03:26
So the top allele, the normal one, will still give you fragment a and then fragment b, but the mutant allele only has two cutting sides.
03:40
So you can see the mutant allure will give you a longer fragment.
03:49
We call it c.
03:50
The c is actually a and b combined.
03:54
So if the genotype of the newborn is heterozygars, then after the mst1 digestion, the dna will give you three different fragments.
04:06
A and b are smaller fragment from the normal allele, and c will be the longer full length from the mutant allele.
04:17
Okay...