DNA Flashcards
name the four base pairs
adenine, thymine, cytosine, guanine
which two base pairs are purine
adenine and guanine
which two base pairs are pyrimidine
thymine and cytosine
what direction do DNA strands duplicate in
5’ to 3’
approximately how many base pairs are their in the human genome
3,000,000,000
how much of the human genome is coding DNA
less than 2%
which two areas of the cell contain DNA
the nucleus and mitochondria
where is nuclear DNA located
on the chromosome
which type of DNA contains STR’s
nuclear
which type of DNA lasts longer and why
mitochondrial as there is more of it in a cell
what can each somatic cell contain in humans
22 pairs of autosomal chromosomes and 2 sex chromosomes
when are chromosomes duplicated
before mitosis
what joins two sister chromatids
a centromere
how many STR loci do we look at in forensics
17
what are the 3 reasons individuals show genetic variation
- genetic recombination
- random assortment of chromosomes
- random pairing of gametes
what is genetic recombination and when does it occur
the exchange of genetic material between parental chromosomes that occurs during meiosis
what is random assortment of chromosomes and when does it occur
when chromosomes separate they all do it differently, resulting in four unique daughter gametes - occurs during meiosis 1
what is random pairing of gametes
mate choice in the physical act of fertilisation
name the three reasons for genetic differentiation
- Barriers to gene flow - migration
- Genetic drift - population size
- Natural selection - non-random mating
describe a novel mutation
the insertion or deletion of a base pair leading to changes in the triplet code for amino acids - frameshift
what are point mutations
transversion or transition
what are the 3 processes involved in DNA extraction
- Extraction - removal of DNA from cellular casing
- Purification - removal of inhibitors from DNA sample
- Isolation - capture of remaining DNA
name 5 things needed for PCR
- Thermal cycler
- Template DNA
- PCR primers
- DNA polymerase
- PCR buffer
what are the three main steps of PCR
- Denature
- Anneal
- Extend
describe the denaturing step in PCR
DNA melts because it is heated to 94 degrees or higher, causing the double stranded DNA to separate
describe the annealing step of PCR
the temperature is reduced to between 40-60 degrees, to allow primers to hybridise to complementary DNA
describe the extending step in PCR
the temperature is then increased to between 70-74 degrees (optimum temperature for DNA polymerase activity), so that DNA polymerase can make new DNA strands
how many primers are used to amplify a single DNA target region and what are they designed to do
2 - forward and reverse - designed to flank the target region for chopping
what does DNA analysis require
two samples - evidence and suspect sample
define DNA profile
a small set of DNA variations that is very likely to be different in all unrelated individuals
how long is an STR
2-6 bp
what makes STR’s specific to individuals
the number of repeats at a specific loci
what do we use to analyse the length differences of STR’s
capillary electrophoresis
what has to be looked at in order to prove that a DNA sample does or does not belong to someone
the probability that it would occur elsewhere in the population
how do we understand the probability that a DNA sample would occur elsewhere in a population
by looking at the frequency each allele exists at within and between populations - by measuring multiple genotypes within populations
how do we measure allele frequency
p + q = 1
why does forensic DNA profiling use more loci with higher polymorphism
as the probability of observing a matching profile is high when measuring he genotype frequency at a single locus with two alleles
why is accounting for population structure when calculating the probability of observing matching DNA important
as it prevents over and understating the evidence
name 4 ways matching DNA profiles can occur innocently
- Mono-zygotic twins
- Severely inbred populations (not human)
- Instances of laboratory error
- DNA transfer events - direct or indirect
