Genome Variation Flashcards
(32 cards)
What is the size of the human genome?
3 billion bases (3000Mb) which is about 20,000 genes
What causes sickle cell anaemia?
point mutation
What causes CFTR?
3bp deletion
How much DNA is the same between any 2 people?
99.7%
What is different in the 0.3% of DNA that is different between any 2 people?
- phenotypic differences between people
- all the differences that are not visible eg blood pressure, cholesterol levels, susceptibility to different diseases
What does polymorphic mean?
any position in the genome that can vary between 2 individuals
What is a major allele on a position?
it is more common (more common variant)
How do we know which gene is normal at that given point i.e. reference DNA?
human genome mapping project
- 4 anonymous individuals had donated their DNA, and whichever allele was most common was determined to be the reference allele
- this reference allele is what is expected, and is considered normal
- when a position in the genome deviates from that reference, it is called a polymorphic site
What is a polymorphic site?
when a position in the genome deviates from that reference, it is called a polymorphic site
What is a Single Nucleotide Polymorphism?
change in a single base
How common are SNPs?
very common
find SNPs every 300 bases
through studies= 17 million SNPs have been identified in human genome
How do you get SNPs?
- mutations
- faulty mismatch repair
Explain a faulty mismatch repair:
see mohib’s notes page 3
What happens if a SNP happens during meiosis?
lead to polymorphism which goes onto next generation
What type of a difference do SNPs lead to?
biallelic- means there are only two different alleles involved
Give an example of something that is multiallelic?
microsatellite
Where in the DNA can SNPs occur?
in the gene
promotor region of the DNA
in the large amounts of non coding regions
What happens if SNPs are found in the gene?
- maybe no impact on the phenotype if there are no amino acid changes (synonymous)
- could have impact and result in an amino acid change
- could get stop codon- lead to nonsense mutation
- affect splice sites
- affect an untranslated region which could change gene expression
What happens if SNPs were in the promotor region of the DNA?
changes in protein expression
What is the difference between SNPs and point mutations?
SNPs- no detrimental effect
point mutations- detrimental effect
How can you tell the difference between SNP and a point mutation?
- SNPs can be differentiated from point mutations (which are essentially a change in a single base) by looking at the minor allele frequency
- minor allele= allele which occurs least number of times on polymorphic site
- if the minor allele frequency is more than 1% it is a polymorphism
How does the allele population differ in different places?
eg the sickle cell anaemia allele is more common in African populations (4.5% in Africans whilst 0.02% in Caucasians)
thus using the earlier definition of a polymorphism, the sickle cell anaemia allele is polymorphic in African populations and a mutation in Caucasian populations
Every variant starts off rare. What does this mean?
this means that every base change occurs for the first time only in a very small number of individuals
How does evolution determine whether a gene will stay or not?
- mutation occurs ie a new allele arises and there is a single nucleotide variation
- gene flows around population through migration
- reproduction- further spread of SNP (genetic drift)
- this is random depending on mating partner etc.
- natural selection= single nucleotide variation will get selected and its allele will increase if it is beneficial, and will decrease if it is pathogenic
