Lecture 2 and 3 - History of Molecular Evolution Flashcards
When did the first DNA evolve?
3.6 billion years ago
When was evolutionary synthesis formalised?
In the 1930s
What was known about molecular evolution in the 1940s?
DNA, RNA and proteins were known to be macromolecules.
But little was known about the function of these molecules.
Where did most scientific discoveries come from pre-1940s?
Europe
Describe the work of Griffiths (1928).
- Spanish flu in Europe 1918-19 causing huge numbers of deaths.
- Investigated development of vaccine for Streptococcus pneumoniae.
- Described transforming principle: rough strain mixed with heat-killed smooth strain leads to mouse death.
Describe the work of Avery et. al (1944).
- Added various treatments to genetic material of Streptococcus pneumoniae.
- With protein hydrolysis, DNA is not killed off, so smooth form dominates.
- With DNase added, DNA is broken down, so rough outgrows the smooth form.
- First proof that DNA is the active component causing bacterial transformation.
When and what was Franklin and Wilkin’s work?
X-ray diffraction images suggesting 2 DNA chains.
When and what was Watson and Crick’s work on DNA?
1953
Published model of the double helices, describing base pairing.
What is the Adaptor Hypothesis?
By Crick - 1958
A sequence of bases would bind an adaptor, to the other end of which carried an amino acid.
Who is responsible for the identification of triplet codes?
Marshall Nirenberg and Johann Matthaei (1961)
Describe the work of Fred Sanger (1951).
Determined the amino acid sequence of the two polypeptide chains of bovine insulin A and B.
Developed Sanger Sequencing, a chain determination method.
Describe Sanger Sequencing.
A di-deoxy or chain determining method.
Incubate radioactively-labelled bases and build fragments of varying lengths.
What is a molecular clock?
A technique using the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged.
Describe the work of Zuckerkandl and Pauling (1962).
Noted the number of amino acid difference between animal haemoglobins was proportional to the divergence time as defined by the fossil record.
What does the basic rate of mutation define?
The speed of the molecular clock.
Give the equation for time since divergence of two macromolecules.
t = d (T/D)
Where
t = time since macromolecular divergence
d = observed sequence difference between two macromolecules
T = fossil verified divergence dates between two organisms
D = observed sequence difference between the molecules in two organisms
What is neutral theory of evolution?
There is too much genetic variation within species for more than a small fraction of it to be subject to natural selection.
What did Kimura believe caused evolutionary changes?
- Random fixation of selectively neutral mutants.
- Genetic drift acts on neutral alleles.
What are the three classes of mutation put forward by Kimura?
- Deleterious
- Neutral
- Advantageous
What is the chance of any neutral allele being fixed under drift?
The chance is equal to its frequency in the population.
Give the probability of fixation of alleles in a diploid population.
P = 1 / 2N
What is u?
The rate at which new mutations rise.
Give the probability of occurrence and fixation of a mutation.
K = (1/2N) x 2Nu
What is the probability of occurrence and fixation of a mutant (K) equal to?
The mutation rate (u)
In what kind of populations is the effect of drift stronger?
Small populations
Describe the experiment on red flour beetles.
- Track frequency of b+ allele in 12 pops with 100 indvs, and 12 pops with 10 indvs.
- Start with equal freq of b+ alleles.
- In smaller populations, one population goes to fixation.
Describe the work of Fitch and Margoliash.
Generated one of first molecular phylogenies using cytochrome C protein.
How long did it take to complete the first human genome?
13 years
Describe an example of a genetic rescue attempt.
Florida panthers isolated from mountain lions, in very low numbers. Developed kink in their tail. Attempts of rescue, reintroduce mountain lions, bring new wild type alleles into population.
What is genetic drift?
Random fluctuations in the number of gene variants within a population.
What is probability of fixation dependent on?
- Population size
- Strength of selection on that allele
What are adaptive radiations?
Diversifications of single lineage into species that exploit diverse ecological niches.
What did key regions identified in Darwin’s finches contain?
ALX1 gene – in humans, loss causes disruption of early craniofacial development.
2 distinct variants that matched neatly with beak shape.
