Selection Drift

Question 1

What is micro-evolution? What is macro-evolution? What are the differences between them?

Answer 1

Micro-evolution: selection on small differences in phenotypic traits
Macro-evolution: short period of rapid evolution followed by longer periods of stasis

Question 2

What are w and s? How can they be calculated?

Answer 2

w is the relative fitness of a population.

s is the selection coefficient.

Question 3

What are the four selection models?

Answer 3

1. 2. Complete dominance: the phenotype is determined by
      one of two alleles; the other is recessive
2. Codominance: both alleles are expressed and can be
   recognized in the phenotype
3. Overdominance = heterosis = heterozygote advantage

Question 4

What types of selection there are? How do they affect genetic variation?

Answer 4

1. Stabilizing selection:
   
   • reduce variation
   • more and more individuals are in the optimal state
2. Directional selection:
   
   • shift of trait due to environmental changes
3. Diversifying selection:
   
   • two traits evolve
   • two species

Question 5

What is neutral evolution? What is the effect on the population?

Answer 5

Neutral evolution is undirected changes in allele frequencies arising from
the fact that offspring genetic make-up is a sample of
the parental genomes.

1. Bottleneck effect: near extinction
2. Founder effect: migrations

Question 6

Why accelerated evolution can take place in small populations?

Answer 6

A population established by a single colonization event often shows deviating genetic composition.

• Alleles can increase their frequency rapidly
• You expect that advantageous alleles will quickly go to fixation
• However, random fluctuations (genetic drift) may counteract selection, especially when selection is weak
• Potential for accelerated evolutionary change (adaptive or non-adaptive) in small populations

Question 7

What is Fst?

Answer 7

Fst is a measure for genetic distance.

Question 8

What is it meant for isolation-by distance? Why is it a good model on human genetic variation?

Answer 8

Genetic distance arises by neutral evolution and is counteracted by dispersal and migration.

Physical distance = genetic distance

Question 9

Why the distribution of skin color can’t be explain only by IBD?

Answer 9

• Dark skin protects against damaging effects of UV radiation
• Dark skin protects against degradation of folic acid
• Light skin promotes synthesis of vitamin D, preventing rickets (“English disease”)?
• Light skin is promoted by sexual selection?
• In the end: dark skin colour is more advantageous in tropical climates, but less important at higher latitudes