Molecular Evolution

Question 1

How would you measure evolution by genetic tools?

Answer 1

Sequence alignment
Best alignment reflects true ancestral relationship
- Matching nucleotides are interpreted as unchanged from a common ancestor
- substitutions can be identified
- gaps inserted to maximise the similarity between sequences indicate the occurrence of insertions or deletions
Rates of nucleotide substitution
Establishing the genetic divergence by the number of substitutions in homologous sequences- rate of substitution comparison

Question 2

What is Kimura’s neutral theory of evolution?

Answer 2

The large majority of molecular polymorphisms reflect neutral changes, most substitutions observed in homologous genes are selectively neutral
This implies that gene families mostly evolve through neutral mutations or when mutation affect fitness- purifying selection which prevents change of character

Question 3

What are the two types of selection?

Answer 3

Purifying (negative) selection- selection leading to stabilisation of a trait and reduction in diversity
Directional (positive) selection- function of a protein is improved or when a protein is undergoing adaption to HR environment

Question 4

What is the molecular clock hypothesis?

Answer 4

Got any given lineage the rate of molecular evolution is constant over time
This implies that mutations and substitutions rates in protein coding genes are the same in all lineages - used to establish divergence time between lineages
However the molecular clock varies between taxonomic groups, complicating the use of molecular divergence to date the last common ancestor

Question 5

How can mitochondrial DNA be used as an assessment of evolutionary distance?

Answer 5

High mutation rate
Matrilineage
No/ low recombination
Useful for analysis of intraspecies change 
'Constant' molecular clock
Analysis of hypervariable control

Question 6

List methods of protein evolution

Answer 6

De novo creation
Gene fusion or fission
Gene duplication
Modification by rapid sequence change
Pseudogenisation

Question 7

What is the most likely source of morphological diversity?

Answer 7

Regulatory DNA-duplicated genes
They regulate a whole programme for body plan and organ development
Eg Pax6- eye master gene

Question 8

What are orthologues and paralogues?

Answer 8

Orthologues- between two species have a direct common ancestor
Paralogues- in a single species evolved by gene duplication

Question 9

What makes humans different from apes?

Answer 9

99.5% shared protein coding DNA
Few truly human genes- haemoglobin
Keratin mutation- hair loss
FOXP2- human specific allele- associated with speech
Positive selection on gene mutation for diet, hearing, olfaction

Question 10

What is molecular evolution?

Answer 10

Genetic change in the face of selective dynamics

Examines DNA and proteins