9 - Human genetic variation Flashcards
What does locus mean in genetics?
A place or location in an individual’s genome.
What is a DNA polymorphism?
A DNA polymorphism is an allelic form of sequence difference that is present in at least 1-2% of the population.
Polymorphisms can be single nucleotide (SNP) or thousands of bases.
Vary in size and type between chromosomes and individuals.
What is the difference between polymorphisms and mutation?
Polymorphisms may or may not have phenotypic effects, most are old and have been passed down through many generations.
If below 1-2% frequency in a population it is called a mutation. It may even be very rare because it has just appeared (de novo).
Mutation indicates a connection with phenotype.
What are the 4 types of polymorphic (mutant) DNA sequences?
SNP - Single nucleotide polymorphisms (E.g. A to G).
Microsatellites - Short tandem repeats (STR) or simple sequence repeats (SSR) E.g. 2-7bp = [CAG]n.
Minisatellites - Variable number tandem repeats (VNTR) 8 to >50pb = [CGT…TAG]n.
CNV - Copy number variant 0,1,3 or more copies of a large stretch of DNA sequence (>1000bp).
What is an allele?
Allele is the term given to the specific DNA sequence present at any given polymorphic locus.
What is repetitive DNA and the two types?
Strings of A,C,G,T nucleotides repeating themselves in patterns.
Types:
- Highly repetitive DNA
- Middle Repetitive DNA
What is an example of highly repetitive DNA and where is it found?
Satellite DNA - found in long tandem strings or arrays
Located near telomeres - ends of chromosomes and around the centromeres - middle of the chromosome.
What is an example of satellite DNA?
α-satellite DNA (alphoid)
- functions in the centromere of chromosomes.
- Repeats extent for millions of base pairs.
- Each repeat unit contains smaller repeat units between 4 and 32bp.
What are mobile DNA elements and the 2 types?
Mobile DNA elements: middle repetitive DNA 2 types:
Transposons - DNA based
Retrotransposons - RNA intermediate.
Mobile DNA elements are DNA sequences that can change their position in the genome.
Mobile DNA elements encode the proteins needed to cut them out, copy them and insert them elsewhere in the genome.
What has become of (retro)transpons and what is an example of an inactivated gene due to (retro)transposons?
Often polymorphic (a lot of variation) between individuals.
Most retrotransposons inactivated through mutation over human evolution.
Movement to a new locus in only 1:100-200 births.
Vitamin C synthesis no longer possible in humans due to inactivated genes.
What are the 2 types of tandem repeats?
Tandem repeats - middle repetitive DNA
2 types:
- Microsatellites
- Minisatellites
What are 3 characteristics or micro/mini-satellites?
Many show polymorphic variation in repeat number and hence variable length.
found throughout the genome - can be in coding regions.
Different individuals/ chromosomes have different numbers of repeats.
What are 7 applications of polymorphisms?
RFLPs: restriction fragment length polymorphisms.
Forensic sample identification.
Biodiversity.
Food quality.
Ancestry/ archaeology.
Preparing to sequence the human genome.
Mapping of disease genes.
What are restriction enzymes and what are they used for?
Bacterial enzymes that act as a primitive immune system.
They cut (restrict) a specific phage (viral) DNA sequence.
Used by researchers as a molecular tool.
RFLP - STR/ microsatellite polymorphisms detected by restriction enzymes.
What is DNA fingerprinting and what is it used for?
Techniques used to distinguish the unique combination of polymorphisms present in an individual.
Originally used VNTRs
Used:
- To identify criminals
- In paternity cases
- In disaster body remains identification.
