UNIT 3 - D 1.3 - Mutation and Gene Editing Flashcards
How can genes be modified?
When one or more letters in a sequence is deleted, inserted or substituted for another letter
What can result from gene mutations?
for some organisms, severe health problems or death, but mostly there is little effect, for some organsisms it gives them advantages
What do beneficial mutations create?
A new version of a gene that will result in a trait giving the organism an advantage in survival
What is a mutation?
a random, rare change in genetic material
When might a mutation occur due to a change in the sequence of bases in DNA?
If DNA replication didn’t work properly
What would happen within mRNA if a DNA a base was swapped with another?
The corresponding bases in mRNA would be altered during transcription
What is a substitution mutation?
When one base is replaced by another
What is an insertion mutation?
When a base is added
What is a deletion mutation?
When a base is removed from a sequence
What is a point mutation?
When only one nucleotide base is involved
What is the locus?
the position
What is GNAT2?
a gene which controls the protein transducin
What does transducin do?
enables colour vision in humans
Where is GNAT2 found?
on chromosome 1
What would a mutation of GNAT2 result in?
stopping an individual from being able to make transducin properly which is needed to transport information about colour from the eye to the brain and therefore, the person would not be able to see colour
What results when a gene sequence is altered by one letter in a base substitutional mutation?
a single-nucleotide polymorphism (SNP)
What can SNPs do?
define different versions of genes, some can explain genetic diseases and cancers
What could be a consequence of changing one base?
a different amino acid is placed in the growing polypeptide chain
What does the mutation in the genes of haemoglobin do?
alters shape of the haemoglobin molecule and the red blood cell no longer looks flattened and hollowed out
What disease results form gene mutations in haemoglobin?
the sickle cell disease or sickle cell anaemia
What results in a haemoglobin molecule having different properties causing the complications of sickle cell disease?
the bases GAG becomes GTG in the second codon, therefore valine is added during translation instead of glutamic acid, and because valine has a different shape and different properties, the shape of the polypeptide chain is modified`
What is huntington’s disease caused by?
a dominant allele
What does huntington’s disease cause?
nerve damage, though symptoms are not shown until age of 40
How is huntington’s disease caused?
when a gene called huntington (HTT), found on chromosome 4, has an insertion mutation where multiple copies of three nucleotides, CAG, are added to the gene
What kind of mutation is involved in huntington’s disease?
trinucleotide repeat expansion
Which amino acid has its code repeated from the CAG trinucleotide (involved in huntington’s disease)?
glutamine
What can dictate the severeness of a person’s symptoms of huntington’s disease?
how many trinucleotide repeats the person has
How many repeats does a person need before they are affected and see symptoms of huntington’s disease?
40 repeats
What is a frameshift?
a phenomenon that happens when an insertion or deletion occurs in non-multiples of three
What happens when a letter is added to a genetic sequence as a result of a mutation?
the code is shifted
When will the other codons remain unchanged if a mutation occurs?
if the code is shifted by three new letters being added or three being deleted
What may happen if an insertion or deletion is not a multiple of three?
the code changes drastically, not make sense anymore, could transform a normally coding codon into an unexpected stop codon
When does a normally coding codon turn into an unexpected stop codon?
When the DNA proofreading the system tries to repair a mistake and the DNA polymerase may reattach in the wrong place along the sequence it is trying to repair
What are leucocytes?
white blood cells
What are chemokines?
chemical signals which tell leucocytes where to go in order to find invaders such as viruses
What do special proteins on the surface of leucoyotes do to follow the message of chemokines?
they act as receptors to pick up the chemicals
What is an example of a molecule which helps form a receptor for the receival of chemokines on leucocytes?
a co receptor molecules called C-C chemokine receptor type 5 or CCR5
What is one type of human immunodeficiency virus?
HIV-1
What puts people with functioning CCR5 genes on chromosome 3 and can make a functioning version of the special protein for their CD4 cells at risk of HIV-1 entering their cells?
HIV-1 being able to use the receptors on leucocytes as a point of entry to infect leucocytes (CD4 cells)
What will eventually happen to a person who is HIV-positive but is not getting any treatment?
their leucocytes will continue to be destroyed and the person will no longer be able to fight off other infections
What does AIDS stand for?
acquired immunodeficiency syndrome
When does a person have AIDS?
at the point when they have HIV and haven’t been treated and they cannot fight off other infections
What is the delta 32 mutation or CCR5-delta32?
a mutation of the CCR5 receptor gene
What kind of mutation is the delta 32 mutation?
a deletion mutation where 32 nucleotides are removed
How is a stop codon formed (where it shouldn’t be) due to the delta 32 mutation?
because 32 is not a multiple of three, there is a frameshift and a stop codon is formed
What allows people to be highly protected from HIV infection?
Becuase the stop codon formed by the delta 32 mutation makes the ribosome stop producing the special protein early, people with this mutation cannot have functioning chemokine receptor protein which HIV-1 needs to infect their leucocytes
How can exposure to ionizing radiation or mutagens cause serious health threats like cancer?
It can sometimes modify the DNA code (which shouldn’t be modified during the lifetime of an individual) causing these issues
What are mutagens?
chemicals that can cause a genetic mutation
What is over exposure to sunlight linked to
melanomas (type of skin cancer)
What is an example of mutagens that come from within the cell?
certain enzymes that attack DNA and can transform the identity of a nitrogenous base
What is an example of a mutagen which can come from the outside environment of a cell?
benzene which is used by industries to make other molecules that people use daily
What can benzene cause?
leukaemia
What can happen when radiation hits a DNA molecule?
it can knock one or more base pairs out of place, modifying the genetic code
What are two examples of when people and the environment were exposed to radiation?
chernobyl (1986) and fukushima (2011)
What is one of the simpler ways a mutation could occur in the genetic material?
During DNA replication, while letters are being added, a wrong letter could be added
What usually happens when a simple error is made in adding the wrong letter to the polymer?
The error is corrected durning the DNA polymerase’s proofreading process
How can errors involving the wrong letter being placed in the polymer chain be corrected?
the incorrect bases can be replaced by the expected ones
Why might some genes or sequences have a greater chance of being mutated?
if it has more than one copy and weather the DNA is coiled or uncoiled
What does having an original copy of a gene allow?
the extra copy can tolerate mutations
Why does uncoiled DNA have a higher probability of undergoeing a mutation?
because the uncoiled DNA is more exposed
Where can mutations occur?
anywhere that sequences of nucleotides can be found
Where can mutations occur in humans?
on any of the 22 autosomal (non-sex) chromosomes or on the X or Y sex chromosomes
Why is it more likely for mutations to occur on the non-coding zones of the genome?
because only 1-2% of the human genome codes for proteins
how can mutations on non-coding genome still affect the production of proteins?
because these zones of genome contain regulatory sequences that can turn coding sequences on and off
What is an example of non-coding DNA used for structural purposes?
satellite DNA
Where can satellite DNA be found?
in the centromere
Where can mutations end up being responsable for generating new strains of viruses that are more dangerous or that can spread faster?
mutations found in other animals, bacteria, fungi, archaea, and plants
What are mutation hotspots?
zones where mutations are more frequent
What is an example of a mutation hotspot?
where the nucleotide cytosine is followed by guanine
What are CpG sites?
where cytosine is followed by guanine
When does the C in CpG sites mutate into a T?
when methylation happens
What are CpG islands?
Places where CpG sites repeat
What are CpG islands more likely to do?
generate mutations
What do somatic cells do for division to grow tissues and organs in the body?
mitosis
what do germ cells use to produce gametes (sperm and egg cells)?
meiosis
When can mutations be passed on to offspring?
when they occur in germ cells
Why might all cells in a child contain a mutation?
If the cells making sperm cells contributed to the zygote’s mutation because all other cells in the child come from the zygote
what is an organism’s germ line?
eggs, sperm cells and zygotes
what cells make up an organism’s germ line?
cells involved in passing on genetic information to offspring
What did each genetic disease that currently exists in the human population start out as?
a mutation that was passed down from generation to generation
When would a mutation not be passed down to offspring?
if the mutation happens in a somatic cell
What are mutations in somatic cells associated with?
cancer and tumours
What is a beneficial mutation which is likely to be passed on to the next generation?
a mutation that provides an individual/species with a better chance for survival
What are detrimental mutations which are less likely to be passed to the next generation?
Mutations that cause disease or death
Why are detrimental mutations less likely to be passed to the next generation?
because they decrease the individual’s chance of survival
What does a mutation become when it is successfully passed down from one generation to another?
a new allele (a new version of the orginal gene)
What determines weather a mutation is harmful, beneficial, or neutral?
what environment we need to survive in
Why is it important that new alleles are produced?
because if not, we would be only passing on existing genes and nothing new would appear
What is gene knockout?
a procedure involving rendering a gene unusable to see what effects it has on an organism
What is a knockout organism?
an organism whose gene has been knocked out, such as a lab mouse
What is one important use of knockout mice in labs?
to test pharmaceutical drugs
What is a model organism?
an organism used in place of another for practical/ethical reasons
What are the advantages of using mice in gene knockout (instead of humans)?
they have similar metabolic systems as humans, share many of the same genes, easy to maintain in lab, reproduce quickly so many generations may be tested in a short time period
What are some conditions that have been studied using knockout mice?
obesity, diabetes, anxiety, longevity, likeliness to develop certain cancers, substance abuse/addiction, cardiovascular disease
What is CRISPR-Cas9?
gene-editing technology developed in 2012
What are the two main parts of CRISPR-Cas9?
The Cas9 enzyme and a guide RNA
What does the Cas9 enzyme do for CRISPR-Cas9?
it works like scissors to cut DNA
What does the guide DNA do in CRISPR-Cas9?
it acts as a guide showing the Cas9 enzyme where to cut
What does CRISPR-Cas9 do?
as an RNA-guided gene regulation system, it uses a programmable protein (Cas9) to remove/replace genetic sequences
Why can CRISPR-Cas9 work on any organism?
because the genetic code is universal
What are the two possible outcomes of CRISPR?
either the mutated gene can be removed/replaced or the attempts by the cell to repair the cut may lead to errors like frameshifts which make the gene inactive
How could CRISPR treat an embryo with down syndrome?
by deleting the entire third 21st chromosome
What is a gene drive?
a mechanism that increases the chances of a gene being passed down to the next generation
What would be involved in off-target effects of CRISPR?
if the editing technology accidently changes a part of a genome that was not supposed to be modified
What are conserved sequences in genetics?
genetic sequences found in DNA or RNA that show minimal mutations over time
What are highly conserved sequences in genetics?
genetic sequences found in DNA or RNA which show no/almost no changes over time
When were conserved sequences and highly conserved sequences first noticed?
When researchers started sequencing genes and comparing them between species and between individuals
What is an example of highly conserved sequences?
the sequences needed for all cells in all species such as the sequences that make DNA replication, transcription, and translation possible
What are genomics?
gene sequencing science
What are bioinformatics?
using computer programs to analyze large data sets)
What are the two hypotheses explaining why mutations/evolutionary modifications affect some sequences less than others?
- the functional requirements of the gene are such that an organism cannot live without it
- some sequences are subject to slower mutation rates than others
What does the functional requirements hypothesis involve as to why mutations affect certain sequences more than others?
it says that natural selection conserves sequences necessary for the cell’s survival and does not let any mutations pass down to the next generation
What is purifying selection or negative selection?
a type of natural selection which is the phenomenon of eliminating harmful variations of genes
What is the mutation rate?
how many changes there are in a genetic sequence over time
What can the mutation rate be expressed as?
the number of base pairs changing in a single gene at each generation or as the number of base pairs changing in the whole genome per generation
Why is it more likely to find higher mutation rates in non-coding DNA like satellite DNA?
because it does not undergo purifying selection and because the DNA repair system is more active in key zones of the genome where errors would have more severe consequences
Where is the proofreading function carried out by DNA polymerase less active?
in places where mutations would not lead to life-threatening issues such as non-coding DNA and genes that have been silenced
What could increase mutation rate?
if a mutagenic chemical or if radiation like UV light were present
