Human Molecular Genetics Flashcards
what were the 5 aims of sequencing the human genome?
to find out what genes make up the genome and what their role is
to get information out to people and scientists asap
analyse genetic variation between humans
sequence the genomes of several different model organisms
develop new sequencing techniques and computer analysis
6 key findings of sequencing the human genome
the genome is dynamic
fewer genes then expected
less then 2% of the genome codes for proteins
still dont know what many of our protein coding genes do
most human genes are related to animals
humans are 99.99% simular at sequence level
what are SNP’s
linked vs causative
single nucleotide polymorphisms
1 in every 3 nucleotides
linked - outside of the gene, they have no effect on protein production or function
causative- non coding SNP’s changes the amount of protein produced
coding SNP- changes the amino acid sequence
What are STR’s
short tandem repeats
repeats of 2-5 nucleotides found in specific regions of the genome
receive 2 alleles one from each parent
eg STR site
8 repeats of CAG from mother
3 repeats of CAG from father
this person is 3,8 at STR 1
What are indels?
small insertions or deletions
second most common varient type in human genome
can cause a ‘frame shift’ in the way DNA is read eg insertion of one letter or deletion in 2 letters
what are structural variants
CNV’s
copy number variations- chunks of DNA more than 500 base pairs that are present at different amounts
deleted or duplicated
can span multiple genes
many associated with sensory perception and immunity
what is comparitive genomics used to discover?
what is in common and what is different
common = conserved
what does different genomics mean
That it may encode organism specific biology
what may conserved genomics encode?
biology in common between species
what may genetic differences be associated with?
disease
charactaristics of an individual
evolutionary history
what can we learn about an organism if we compare its genome to others
what sort of genes that they have
how differences between species arise
relationships between species
germline mutations
can be inherited and passed on via the gametes
somatic mutations
occuring in the somatic cells they cant be passed on
they happen if DNA gets damaged or copied incorrectly
loss of function mutation
doesnt do enough function
often are recessive because a normal copy of the gene exists on the other chromosome which can replace the loss of function
gain of function
where one gene is working too hard
often dominant and will not be replaced by the normal copy of the genea
autosomal recessive genes
typically not seen in every generation of affected family
passed on by two asymptimatic carriers
males and females equally likely to inherit
autosomal dominant
occurs commonly in a pedigree
affected individuals have an affected parent
Males and females equally likely to inherit
widows peak
huntingtons disease
X linked recessive
fathers cannot pass X-linked traits to their sons
No male- male transmission
Most often affects males
eg haemophilla A & B
how to find potential disease genes
sequence the genome- compare against standard genome.
identify common variants
different variants- predicted to be benign
predicted to be harmful- validate and test
how to find polygenic disease genes?
cases and controls (10-10000)
identify the variations
common variants
shared variants in cases that arent in the controls
validate and test- are variations in the disease likely to be associated with the disease?
genetic determinisim of disease
just because you have the variation of a disease doesnt mean you will have the disease
they come through a combination of variants and the envrionment
genetic disorders are probabilistic not deterministic
how to get information about the function of a gene from its phenotype
studying organisms that are naturally mutant for a particular gene, we can work out what that gene might go
where no natural mutants exist we make our own
by studying both of these types of mutants we can learn how particular mutations lead to phenotypic changes
example of a natural mutant and what is the normal function of the gene
polydactyly- 6 fingers
the natural mutant is the cause of the phenotype
the normal function of this gene is to produce 5 fingers
4 ways to use genetic techniques to find out what a gene does
study organsims naturally mutant for that gene
increase the rate of random mutation, select for a phenotype of interest and sequence the genome to identify the mutation
transgenesis
targeted mutation
what is the process of transgenesis
taking a gene of interest, copying it and inserting it into another organism
eg flouresent gene from jellyfish and putting it into a pregant mouse so the mouse then have flourescence.
how to target mutations to the DNA sequence
damage or modify the gene we are interested in by genetically modifying an organism. Examine the organism or offspring we then work out what the gene normally does.
what are the components of CRISPR- Cas9
CRISPR- clustered regularly interspaced short palindromic repears
Cas= crisprs associated protein incolged in bacteria for aniviral defense
how does crispr cas know what DNA sequence to cut
there is a designed short guide RNA that only binds to the gene of interest so it knows which DNA to cut
what happens once CRISPr Cas9 enters the cell
enters the nucleus and finds the target sequence in genome that matches the guide RNA
the Cas9 makes the double stranded cut in dna at the target site
what are the consequences of a cell trying to repair cut DNA without a template
The DNA repair enzyme trys to mend the cut without template to read from so there are errors.
Creates small indels at the target site so the gene becomes disrupted or mutated
what are the ways to potentially fix genetic disease in somatic cells (with examples)
gene therapy- cystic fibrosis. Delivering dna with functional copy of the CFTR gene to the lung epithelial, the extra copy of the gene makes a good CFTR protein which can restore the function of some cells
gene editing - CRISPR Cas9- eg sickle cell disease
examples of how germline genetic disease can be fixed
pre implantation genetic diagnosis- IVF
three parent babies- the nucleus containing the genetic information from a cell with diseased mitochondria is implanted in the cell of a host cell with healthy mitochondria. Nuclear DNA from biological parents and mitochondrial dna from a healthy donor.
what does totipotent mean
when a cell is able to give rise to all cell types through cell division (including placental cells)
what does pluripotent mean
when a cell can give rise to all cell types ( except placenta)
what happens to cells during embryo development
cells become more specialised and less flexible, except for stem cells and germline cells
explain how embryonic cells are not differenciated
embryonic precursor cell- mastor regulatory gene is off and muscle specific genes arent being transcribed therefore no protein being created
when the myoblast is determind the mastor regulatory gene is turned on and myoD protein (transcription factor) are activated.
fully differentiated part of a muscle fibre developed- different transcription factors are turned on which produced things such as myosin and other muscle proteins
embryonic stem cells
harvested from inner cell mass of blastocytes
pluripotent- can develop into any of the 200 cell types in our bodies
cells from embryonic stem cells genetically identical to embryo doner
induced pluripotent stem cells
made by reprogramming adult skin cells
pluripotent
made from anyone and are genetically identical to the source skin cells
adult tissue stem cells
stem cells dividing without limit
undifferentiated- multipotent cells
only give rise to 2,3,4 different types of cells
umbilical cord stem cells
stem cells from blood isolated from the umbilical cord of newbord babies are frozen
they are multipotent
immature blood stem cells
can be used to treat leukemia or other blood diseases
where are blood stem cells found
in haematopoietic stem cells found in bone marrow- can be used for transplants
why are stem cells important for certain tissues
blood and skin
because they need constant renewing
what does culture conditions do to stem cells
different culture conditions used to persuade cells to develop and differentiate into different types of cells
eg embryonic cells in different cultures differentiate into liver cells, nerve cells or blood cells
what is the idea of regenerative medicine
pluripotent stem cells can be used to repair or replace damaged organs or tissues
pluripotent stem cells (skin or blood or embryos)
encouraged to differentiate into specific cell types eg neurons
these can be transplanted into patients
eg IPSC-derived corneal transplants
stem cells in gene editing
stem cells can be edited or used with gene therapy to ‘fix’ genetic disease in patients, the corrections to the DNA are passed on to all daughter cells
