4 - Evolution And Speciation

Question 1

Three main mechanisms of micro evolution

Answer 1

Natural selection
Genetic drift
Gene flow

Question 2

Micro evolution def

Answer 2

Changes in allele frequencies in a population of a species over time

Question 3

Postulates by Rosemary and Peter Grant to prove Darwin’s theory (1976-1978)

Answer 3

1 - for any particulate trait, individuals within a species are variable
2 - some of this variation is heritable
3 - reproduction is not random; individuals that reproduce the most are those with the most favourable variations - survival of the fittest

Question 4

Evidence for postulate 1

Answer 4

Variable beak depth for different ground finches

Question 5

Evidence for postulate 2

Answer 5

• parents with small beaks tend to have offspring with shallow beaks
• parents with deep beaks tend to have offspring with deep beaks
• this there is a large genetic component to determination of beak depth

Question 6

Evidence for postulate 3

Answer 6

• a drought reduced the number of seeds available - many birds died
• the seeds that were produced were larger and harder in the drought than they were before or after
• selective pressure arised
• the next generation of birds had a larger selection for deeper, stronger beaks

Question 7

How do populations adapt

Answer 7

Adapt genetically to the environment
Micro evolution by natural selection is therefore a theory and a fact

Question 8

Evolution def

Answer 8

Change in inherited traits of a population through successive generations: the genetic content of a population changes over time
- via mutations

Question 9

Dominant advantageous alleles visibility

Answer 9

Heterozygous and homozygous dominant (Aa and AA) are both visible
- these alleles will rapidly rise in frequency of population

Question 10

Recessive advantageous allele visibility

Answer 10

Only visible to natural selection as homozygous recessive
- take a long time to accumulate, so fixation in a population takes longer

Question 11

How mutations with no selective advantage change in frequency in populations

Answer 11

Doesn’t occur by natural selection
Occurs by genetic drift

Question 12

Modelling genetic drift by sampling error

Answer 12

Not all gametes contribute to next generation
- so expect sampling error
Modelling suggests genetic drift will fix alleles in a population

Question 13

Richard Lenski, long term evolution experiment (LTEE)

Answer 13

E. Coli can use glucose as a C source in aerobic conditions, but cannot use citrate in aerobic conditions

Question 14

Why E. Coli can’t use citrate in aerobic conditions

Answer 14

• anaerobic conditions: expresses a citrate transporter, can take up citrate from growth medium
• aerobic conditions: citrate transporters not expressed, so E. Coli cannot utilise external citrate as energy source (Carbon source)

Question 15

How E. coli in LTEE evolved to use citrate in aerobic conditions

Answer 15

Mutation in Cit strain
- duplication of gene encoding citrate transporter
- de-regulated expression
- so citrate transporter expressed in aerobic growth
- Cit strains now can utilise as well as glucose as C and energy source
- gives them a selective advantage

Question 16

Gene flow def

Answer 16

The movement of alleles between previously separate populations

Question 17

How do alleles move/shift in a population

Answer 17

Migration of adults and subsequent mating movements of gametes (e.g. pollen) and subsequent fertilisation

Question 18

Three main mechanisms of population divergence - that leads to speciation

Answer 18

1. Genetic drift - removes genetic variation within demes (sub populations) but leads to differentiation between demes
   - all by random change in allele frequencies
2. Gene flow introduces new alleles into demes with a metapopulation
   - by itself can lead to genetic homogeneity between demes
3. Selective and reproductive isolation

Question 19

Species def - eukaryotic level

Answer 19

A population of organisms that can potentially or actually interbreed, giving viable fertile offspring
- species are reproductively isolated from other groups - different species cannot reproduce together

Question 20

The Tube mosquito case study

Question 21

Experimental evidence of speciation

Answer 21

The Tube mosquito
Tree frogs and chromosomal duplication
Male Geospiza conirostris flying to Dapne Major from Isla Espanola - Big Bird Lineage

Question 22

Double line meaning on a family tree meaning

Answer 22

Consanguinity - two offspring mated with each other