Lecture 2 and 3 - History of Molecular Evolution

Question 1

When did the first DNA evolve?

Answer 1

3.6 billion years ago

Question 2

When was evolutionary synthesis formalised?

Answer 2

In the 1930s

Question 3

What was known about molecular evolution in the 1940s?

Answer 3

DNA, RNA and proteins were known to be macromolecules.

But little was known about the function of these molecules.

Question 4

Where did most scientific discoveries come from pre-1940s?

Answer 4

Europe

Question 5

Describe the work of Griffiths (1928).

Answer 5

• 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.

Question 6

Describe the work of Avery et. al (1944).

Answer 6

• 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.

Question 7

When and what was Franklin and Wilkin’s work?

Answer 7

X-ray diffraction images suggesting 2 DNA chains.

Question 8

When and what was Watson and Crick’s work on DNA?

Answer 8

1953

Published model of the double helices, describing base pairing.

Question 9

What is the Adaptor Hypothesis?

Answer 9

By Crick - 1958

A sequence of bases would bind an adaptor, to the other end of which carried an amino acid.

Question 10

Who is responsible for the identification of triplet codes?

Answer 10

Marshall Nirenberg and Johann Matthaei (1961)

Question 11

Describe the work of Fred Sanger (1951).

Answer 11

Determined the amino acid sequence of the two polypeptide chains of bovine insulin A and B.
Developed Sanger Sequencing, a chain determination method.

Question 12

Describe Sanger Sequencing.

Answer 12

A di-deoxy or chain determining method.

Incubate radioactively-labelled bases and build fragments of varying lengths.

Question 13

What is a molecular clock?

Answer 13

A technique using the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged.

Question 14

Describe the work of Zuckerkandl and Pauling (1962).

Answer 14

Noted the number of amino acid difference between animal haemoglobins was proportional to the divergence time as defined by the fossil record.

Question 15

What does the basic rate of mutation define?

Answer 15

The speed of the molecular clock.

Question 16

Give the equation for time since divergence of two macromolecules.

Answer 16

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

Question 17

What is neutral theory of evolution?

Answer 17

There is too much genetic variation within species for more than a small fraction of it to be subject to natural selection.

Question 18

What did Kimura believe caused evolutionary changes?

Answer 18

• Random fixation of selectively neutral mutants.

- Genetic drift acts on neutral alleles.

Question 19

What are the three classes of mutation put forward by Kimura?

Answer 19

• Deleterious
• Neutral
• Advantageous

Question 20

What is the chance of any neutral allele being fixed under drift?

Answer 20

The chance is equal to its frequency in the population.

Question 21

Give the probability of fixation of alleles in a diploid population.

Answer 21

P = 1 / 2N

Question 22

What is u?

Answer 22

The rate at which new mutations rise.

Question 23

Give the probability of occurrence and fixation of a mutation.

Answer 23

K = (1/2N) x 2Nu

Question 24

What is the probability of occurrence and fixation of a mutant (K) equal to?

Answer 24

The mutation rate (u)

Question 25

In what kind of populations is the effect of drift stronger?

Answer 25

Small populations

Question 26

Describe the experiment on red flour beetles.

Answer 26

• 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.

Question 27

Describe the work of Fitch and Margoliash.

Answer 27

Generated one of first molecular phylogenies using cytochrome C protein.

Question 28

How long did it take to complete the first human genome?

Answer 28

13 years

Question 29

Describe an example of a genetic rescue attempt.

Answer 29

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.

Question 30

What is genetic drift?

Answer 30

Random fluctuations in the number of gene variants within a population.

Question 31

What is probability of fixation dependent on?

Answer 31

• Population size

- Strength of selection on that allele

Question 32

What are adaptive radiations?

Answer 32

Diversifications of single lineage into species that exploit diverse ecological niches.

Question 33

What did key regions identified in Darwin’s finches contain?

Answer 33

ALX1 gene – in humans, loss causes disruption of early craniofacial development.
2 distinct variants that matched neatly with beak shape.