Lecture 23

Question 1

Some mechanisms of evolution

Answer 1

1. mutation
2. Genetic drift
3. Natural selection
4. Sexual selection
5. Gene flow

Question 2

Mutation

Answer 2

• ultimate source of all genetic variation
• change the genetic code which generates new alleles, which may change amino acid sequence or gene expression, which may have phenotypic effects

Question 3

Mutation - Deleterious

Answer 3

• decrease fitness (survival and reproductive success)

- average mutation reduces fitness by about 2% per generation

Question 4

Mutation - Benefits

Answer 4

• few beneficial mutations are likely to be of small effect
• most things are fairly good at surviving so helpful mutations mostly just tweak things
• “Hopeful monster” are rare - “beneficial mutations

Question 5

Genetic Drift

Answer 5

• causes random changes in allele frequency
• Calculate frequency by adding up # of one types of alleles and dividing by total # of alleles
• Evolution happened but it was completely random
• is stronger in smaller populations (can be seen in computer simulations)
• Eventually half the population will fix for the allele and the other half will fix for the other allele, if there are 2 alleles in total

Question 6

“Quantitative” genetic variation

Answer 6

• Traits influenced by multiple gene (polygenic)
• usually influenced by environmental conditions
• typically leads to continuous variation (most alleles have a continuous distribution)
• changes in allele frequency at multiple genes underlie genetic changes in quantitative traits

Question 7

Two complementary ways of looking at evolutionary change

Answer 7

• changes in allele frequency

- changes in mean values of quantitative traits

Question 8

Natural Selection (quantitative traits)

Answer 8

Darwin’s and Wallace’s insight

• All organisms have the potential for exponential growth and yet most populations remain relative stable in the # of individuals: this implies high mortality in nature
• traits vary among individuals
• traits influence survival
• traits are heritable

Question 9

Natural selection (prediction)

Answer 9

• traits that improve survival should increase in frequency (or size) through time
• Darwin used domestic breeds (pigeons) as an example of the power of the selection
• Ex. Ecological changes caused by 1976 Daphne Major drought (seed abundance decreased, average seed size and hardness increased)
  G. Fortis (bird)
• Approximately 90% of all individuals died during this drought
• used a capture-measure-mark-resight method to view birds
• See whether the beak size influenced survival (were the birds with longer beaks recaptured?)
• Certain traits influenced the survival of birds (individuals with larger/deeper beaks were more likely to survive, traits are heritable: relationships btwn beak size of parents and offspring)
• Weak sizes were larger in the next generation
• Selection and evolution are highly variable

Question 10

Sexual selection

Answer 10

Intra-sexual: male-male competition

Inter-sexual female choice (widow birds)

Question 11

Why do male mosquitofish have such long gonopodia?

Answer 11

Natural and sexual selection often act in opposition to each other

• It aids in sneaky copulations and it impresses females
• So then why isn’t it longer? It is a real drag/causes drag

Question 12

Gene flow

Answer 12

• movements of gene among populations
• tends to oppose the divergent nature of natural selection
• exchanging individuals btwn the 2 selections line of Drosophila would reduce their divergence