-dr ma mon · pseudo-genes: they look like genes but they aren't functional. 2 ... transposons...
TRANSCRIPT
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-Dr Ma’mon
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We have talked about sequencing techniques and how science have developed from needing 12 years to get the full human genome in 2007 to being able to sequence anybodies genome in just 2-3 hours nowadays.
Scientists used to say that 97% of the human genome is junk DNA but a new
paper came out in 2012 and it said that 50-60% of the human genome is
relevant.
The human genome can be divided into:
- inter-genic sequences - Gene related sequences - coding sequences (which are the ones that make proteins)
Repeated sequences: the same pattern of bases repeated several times.
Pseudo-genes : they look like genes but they aren't functional.
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Repeated sequences
-Repeated sequences make up about 51% of our genome
An example on satellite DNA is centromeres and telomeres.
Tandem repeats come one after the other kind of like
telomeres but smaller.
Dispersed repeats are repeated sequences that are scattered along the DNA.
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Macro satellites:
Regions of 5-300 bp repeated 10^6-10^7 times
Centromeric repeats (171 bp) unique to each chromosome (you make
chromosome-specific probes)
Telomeric repeats
Mini satellites(VNTRs):
20-100 base pairs repeated 20-50 times and are tandemly repeated.
They are very important in disease diagnosis they are called VNTRs (variable
number tandom repeats).
They vary according to individuals like while having it one the same
chromosome on the same site, someone might have it 35 repeats while
someone else might have it 25 repeats.
So the sequence itself is of no importance but the number of repeats is
Important.
:
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Micro satellites(STR):
2-10 base pairs repeated 10-100 times
Again the sequence itself in of no importance but the important thing is the
number of repeats.
STR: short tandem repeats
Polymorphism among VNTRs and STR
Remember we are diploid so someone might have inherited different
repeats from both parents which yield different patterns even among
siblings.
Here PCR is applied because VNTRs and STR vary a lot among people.
Primers are used to surround the repeats.
The result of the PCR is used in forensics and maternity testing.
We distinguish the results by using gel-electrophoresis (the longer the
repeat the bigger the DNA piece is and the less it travels).
We now use STRs instead of VNTRs because they give more variability.
-This video might make it easier https://www.youtube.com/watch?v=DbR9xMXuK7c
We might encounter 2 people with the same alleles for 1 STR that’s why we use more than just one STR to make the probability of mistakes much less .
EXP: Individual A has got 3 and 10 repeats (heterozygous) so he gives 2 bands while
individual B is homozygous for 6 repeats so he gives 1 band and this is what we call
genetic finger printing (like finger prints the likelihood of 2 people having the same
finger print is unimaginably low) so the likelihood of two people having the same
repeats is extremely low.
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Real life example:
In this example we have grandparents who give a daughter and the other grandparents
give a son and the two of them give a bunch of offspring we can see that we have (4)
types of this STRs (1/3/4/6) repeats and by using gel-electrophoreses we were able to
know what the genetic-finger print of each one is ( keep in mind that some of them have
the same finger print for this STR that is why we use more than one STR in forensics and
other fields of this application ).
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Single nucleotide polymorphism (SNPs)
A single nucleotide base substitution for another at certain locations in our DNA, so basically we have the same gene at the same place on the chromosome
but while some people might have a (G) at a certain place others might have a
(T).
The difference between SNPs and a mutation is that SNPs happen in more
than 1% of the population (keep in mind they are mutations but they happen
so frequently that they are considered kind of normal).
Remember that mutations don’t have to be harmful (actually natural selection is kind of based on mutations) like blue eyes they are caused by a mutation but aren’t harmful
SNPs might be:
- Linked
- Causative
- Aren’t relevant
Linked means that they just happen to exist when a certain pheno-type is present
(they don’t cause it)" they guide us to the diseases gene".
Causative means they cause a certain pheno-type (they might be coding or non-
coding) coding means they are present in the area of the gene that gives proteins
while non-coding means they don’t give proteins but they affect other regions
including (promoters) they don’t change the amino acids but they change the activity
of the genes.
They are important in many fields including "pharmaco-genetics" where people need
different doses of the same drug to get the same effect
https://www.youtube.com/watch?v=tJjXpiWKMyA
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Transposons (jumping genes)
Genes which can change their location on the chromosome
They are either: - DNA transposons(2-3)% of our genome - RNA transposons(retro) which give:
long interspersed elements LINEs
Short interspersed elements SINEs
When the disease is caused by a transposon it's mostly of viral origin
Most of them lost the ability to change location
Some of them have the ability to change their location
When they change location they might jump inside a gene a affect it
causing a disease or they might "jump" to a location which affects the gene
or they mightn’t cause anything if they are far enough
-The doctor didn’t really emphasize on the list of diseases caused by transposons
https://www.youtube.com/watch?v=IPILDcABRkI
Transcription
General information before we start :
A chromosome is a single DNA molecule (we have 46 of them)
Chromatin: it's a chromosome with its related proteins (histons)
A gene is a region of DNA needed to give a functional
RNA (rRNA/mRNA/tRNA)
-https://www.youtube.com/watch?v=hywRdDVR76A ***
Cistron: another term for a Gene
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When a mRNA gives more than 1 protein it's polycistronic and when it gives 1
protein it's monocistronic
In bacteria different regions of the same mRNA give different proteins (polycistronic)
Transcription:
Making RNA from DNA
In transcription we use 1 strand of the double stranded DNA as a template to
make RNA (we can use both strands for RNA synthesis but some genes need
specific strands)
The thing that decides which strand to be used are "promoters" (regions of DNA
that guide the RNA polymerase)
The mRNA that is made is complementary to the used strand
The strand used to make mRNA is termed (-ve) sense
The direction of DNA reading is 3' to 5' while the direction of mRNA synthesis is
5' to 3'
polysomes: it's when many RNA polymerases make mRNA from the same
gene at the same time
-https://www.youtube.com/watch?v=mQh5ku9dyJQ ** part 1
- https://www.youtube.com/watch?v=icUBgcwp8QE ** part 2