Investigating the Function of Individual Genes Flashcards
How do we get information about the function of a gene from its phenotype?
By studying organisms that are naturally mutant for a particular gene, we can work out what a gene might fo
What do we do when no natural mutants exist?
Make our own
What can we learn from studying natural and our own mutants?
How particular mutations lead to phenotypic changes
What happens within natural mutants?
Genetic change (mutation) alters the phenotype
What does natural mutants do?
Give us clues to gene function
What is conserved in other animals?
Many of the human genes which have unknown functions still
How many human genes still have unknown function?
Around 4500 (23%)
What can we do to the genes which animals and humans have in common?
Create mutants of them and then we may learn of their functions in humans
What do we study when using genetic techniques to find out what a gene does?
Organisms that are naturally mutant for the gene (rare)
What can we increase to find out what a gene does?
The rate of random mutation, select for a phenotype of interest and sequence the genome to identify the mutation (genetic screen)
What can you do with genes to find out what it does?
Take the gene you are interested in, copy it and insert it into another organism (transgenesis/genetic engineering)
What can you deliberately do to a gene to find out what it does?
Break a particular gene to find out what happens (targeted mutation/gene knockout/reverse genetics)
What is the approach called when using genetic techniques to find out what a gene does?
Functional molecular genetics
What do share with animals?
Many of our genes
What are model organisms?
Ones that can easily be raised in a controlled environment and are easy to manipulate genetically
What does each organism have?
A different approach that works best for making changes to the DNA genome
How can mutants be made?
By treatment of gametes with mutagens such as x-rays or chemicals
What are mutations made by treatment of gametes with mutagens such as x-rays or chemicals?
Random and can give quite dramatic phenotypes
What is the DNA code?
Universal
What is meant by the DNA code being universal?
Any DNA can be used by any organism and interpreted by any cell- even synthetic DNA
What is transgenesis?
Engineering a multicellular organism by adding in “foreign” DNA
What can we use transgenic DNA for?
To understand how genes work, to engineer recombinant proteins (synthetic biology), or in gene therapy approaches
How does transgenesis occur?
A fertilised embryo is held by a pipette and the DNA from the transgender is added through the zone and cell membrane into the male pronucleus hoping it will get integrated into the chromosomal DNA of the organism. The embryo is then inserted into the organism and left to process
How do we know if a gene variant is pathogenic?
Modern genetics targets mutations to the DNA sequence of your choice to “break” specific genes
How can we damage or modify the gene we are interested in?
By genetically modifying an organism or cell line
What can we do by examining the organism or its offspring?
We should be able to work out what the gene normally does
Where did the Cas9 protein come from?
It evolved in bacteria for an antiviral defense
What needs to be decided in CRISPR-Cas9?
Which gene you wish to mutate
What do you do once you have decided which gene you want to mutate?
Design a short “guide” RNA that only binds to your gene of interest and combine this with the Cas9 protein to make a Cas9-guide RNA complex
What do you do with the Cas9-guide RNA complex?
Get it into the cells of interest in the model organism which is not as easy as it seems
What happens once the Cas9-guide RNA complex is in the cells of interest in the model organism?
Cas9 enters the nucleus and finds the target sequence in the genome that match guide RNA
What does Cas9 do once it has entered the nucleus?
It makes a double stranded break in DNA at the target site
What happens once Cas9 makes a double stranded break in DNA at the target site (in the absence of a template)?
DNA repair enzymes try to patch up the cut which often results in errors as there is no template to read from. Small indels are created at the target site, the gene is potentially disrupted or mutated
What happens once Cas9 makes a double stranded break in DNA at the target site (in the presence of a template)?
It is possible to use the repair template to edit the DNA sequence at the cut site (gene editing)
Can we fix a genetic disease?
Yes we can but only if we know what causes it, have a way to correct the defect and have considered ethics
How are somatic genetic diseases fixed?
The cells or organs affected are targeted which does not affect the next generation as it is not a change to the germline
How may gremlin genetic diseases be fixed?
Pre-implantation genetic diagnosis, Three parent babies or CRISPR “gene” edited babies
What is involved in pre-implantation genetic diagnosis?
In families with an identified risk, IVF can be used to make embryos from the parents eggs and sperm. These embryos can be tested before implantation and only healthy embryos implanted
What is the faulty gene in three parent babies?
The faulty gene is on the mitochondrial DNA
How are three parent babies formed?
The nucleus from the fertilised egg of the parents which contains the mitochondrial disease is removed and transplanted into a donor egg which contains good mitochondria and has had the nucleus destroyed
What is the composition of the embryo of three parent babies?
Nuclear DNA from biological parents and mitochondrial DNA from the donor
