Molecular Evolution Flashcards
What is relative fitness (W)?
how well a species is able to reproduce in its environment
Anything that increases fitness is selected for, anything that decreases fitness is selected against and other neutral changed will vary randomly
The average number of surviving progeny of a genotype (compared with competing genotypes) after one generation
What does W<1 mean for the allele frequency?
If w < 1, the frequency of the allele
- will decrease with each generation
- until the allele disappears (negative selection)
What does a W > 1 mean?
If w > 1 the frequency of the allele
- will increase with each generation
- until the allele reaches fixation (positive selection)
How can we use molecular phylogeny to identify ancestors of species?
DNA mutations accumulate over time, so species that share a recent common ancestor will have fewer differences than species that are more distantly related
How do we create a phylogenic family tree?
using sequence data - utilise conservation
What are the medical implications of phylogenic trees?
find antibiotics
substances produced by fungi, which are toxic to bacteria, but not fungi, able to be identified - antibiotics
what is sequence conservation?
DNA sequence that is vital to the survival of an organism does not normally show much evidence of variation. Resistant to change
Most variants in these regions will be selected against as they are likely to have a strong deleterious effect
Which sequences of DNA are most highly conserved?
Enzyme active sites
Structural regions of proteins
coding regions
what affects frequency of genetic variation?
Selection
Mutation
Migration
Genetic Drift
what is the main source of heritable changes in a species
genetic variation
What is migration?
movement of species from a different population to an existing population - new variants enter the existing pool of variants = admixture. Population frequency of specific variants can change purely due to admixture and not be disease related
what is genetic drift
how the frequency of variants changes in a population due to chance in recombination. Not all organisms will pass on their genetic variants to the next gen
Which DNA sequences are moderately conserved?
Signal regions in 5’ and 3’UTRs
Promoters
Which sequences are weakly conserved?
Enhancers (in introns and intergenic DNA)
3rd base of codons
what can sequence conservation be used for?
Cross species comparison can be used to generate an evolutionary profile for a gene or gene family
Cross species conservation allows us to identify the important regions of a gene (and its protein)
This allows us to concentrate on areas that appear to be important in novel genes
what do phylogenetic trees show?
Phylogenetic trees illustrate relatedness of different species/ strains/ sequences
The distance between two entities on a tree is related to how similar they are
closer = more similar
Distance is related to evolutionary pressures and to time
use of phylogenetics in infectious disease
HIV may have been introduced via contaminated polio vaccine containing SIV. Using a phylogenetic tree, can determine which strain of SIV is most closely related to HIV to identify the source
what is gene duplication
duplication of a DNA sequence containing a gene
Typical mechanism is unequal crossing over during meiosis
After duplication = 2 copies of the same gene on one chromosome. One copy can continue original function, while other copy can evolve new functions through changes in the coding sequence and/ or control sequences
what is unequal crossing over
Recombination between sequences that are not the correct sequence but are very similar
Often low copy number repeat sequences
what are the globin genes?
two clusters -
Alpha like are on chromosome 16
has 3 genes and 3 pseudogenes
Beta like are on chromosome 11
has 5 genes and 1 pseudogene
What are the adult Hb compositions ?
alpha-2-beta-2
alpha-2-delta-2
What changes occur to gamma gene from HbF to HbA?
the γ gene control sequences have evolved
so that γ-genes are expressed during foetal life
while the β-gene is expressed during postnatal life
fetal hb is..?
alpha and gamma
postnatal hb is..?
alpha delta and alpha beta
what happens to the total % of Hb throughout development
alpha and beta conc is high at postnatal after birth, gamma reduces
