Lecture 5

Question 1

Conspicuous phenotypic divergence between humans and chimpanzees:
(8)

Answer 1

• Hairless
• Loss of muscle strength
• Delayed post-natal development
• Different suit of disease susceptibilities
• Big brain
• Language
• Complex vocal organs
• Funny noses

Question 2

dN/dS comparisons between humans and chimps reveal:

3

Answer 2

• Individual genes
• Genes grouped into biological processes
• Genes grouped by the tissue they are most abundant in

Question 3

Biological processes affected by positive selection between human and chimps include:
(3)

Answer 3

• Immunity and defence
• Chemosensory and sensory perception
• Spermatogenesis and motility

Question 4

What tissue is adapting at the fastest rate between humans and chimps?

Answer 4

• The genes expressed in the testis

Question 5

Comparing humans and chimps with an outgroup enables us to determine which lineage the changes happened down. This prooved
(3)

Answer 5

• 400/16529 genes displayed positive selection
• 10 genes are evolving adaptively in humans
• dN/dS is lower suggesting that there is more purifying selection occurring

Question 6

An immune protein that is a Hep C viral receptor, appears to be adapting really quickly. Why?
(3)

Answer 6

• Amino acid change is favoured as it gives you resistance to the Hep C virus.
• This is an evolutionary arms race between the viral receptor and the virus
• Most changes are localised to the virus binding region

Question 7

Adh gene in D.melanogaster

Answer 7

Balancing selection acts on the fast/slow polymorphism

Question 8

The MacDonald Kreitman test under the neutral model:

3

Answer 8

• The patters of nucleotide variation WITHIN species should match the patterns of nucleotide variation BETWEEN species
• Input: sequences from within and between species
• Output: reject neutral model (or assumptions of test)

Question 9

Drosophila melanogaster and Adh using the MacDonald Kreitman test:
(4)

Answer 9

• Balancing selection acting on the fast/slow polymorphism (a single aa change)
• Compare the number of non-synonymous and synonymous changes to the polymorphism and divergence
• Perform a chi2 test
• NS favouring aa divergence

Question 10

Dn/Ds = Pn/Ps

4

Answer 10

Ds = divergence per syn site
Dn = divergene per non.syn site
Ps = polymorphism per syn site
Pn = polymorphism per non.syn site

Question 11

This formula can be used to answer the..
alpha = 1 - (DsPn/DnPs)
(2)

Answer 11

• The Selectionist/neutralist debate

- alpha is the proportion of aa substitutions that are adaptive