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Flashcards in Lecture 5 Deck (11)

Conspicuous phenotypic divergence between humans and chimpanzees:

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


dN/dS comparisons between humans and chimps reveal:

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


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

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


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

- The genes expressed in the testis


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

- 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


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

- 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


Adh gene in D.melanogaster

Balancing selection acts on the fast/slow polymorphism


The MacDonald Kreitman test under the neutral model:

- 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)


Drosophila melanogaster and Adh using the MacDonald Kreitman test:

- 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


Dn/Ds = Pn/Ps

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


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

- The Selectionist/neutralist debate
- alpha is the proportion of aa substitutions that are adaptive