Lecture 4: Evolution and Speciation (watch last 10 mins of lecture)

Question 1

Is molecular evidence very powerful evidence when working out lineages?

Answer 1

Yes

Question 2

Who redefined evolution in 1937?

Answer 2

Theodosius Dobzhansky redefined evolution: a change in allele frequency in a gene pool.

Question 3

Who thought that natural selection was the driving force behind evolution?

Answer 3

Charles Darwin

Question 4

Is microeveolution evolution below the species that can be inherited by the next generation?

Answer 4

Yes

Question 5

What was Darwin’s first postulate?

Answer 5

For any particulate trait, individuals within a species are variable

Question 6

What was Darwin’s second postulate?

Answer 6

Some variation is heritable

Question 7

What was Darwin’s third postulate?

Answer 7

There’s a change in the population because of the natural selection of the heritable features

Question 8

Did Darwin have any experimental evidence for his theory of evolution by natural selection?

Answer 8

No

Question 9

Describe how Rosemary and Peter Grant tested Darwin’s hypothesis (1976-1978)

Answer 9

• They noticed that the medium ground finch, Geospiza fortis, showed variation in beak depth.
• They captured every bird on the island and ringed it so that they could identify each bird.
• Every time the birds mated, they measured the size of the beaks of the offspring
• There was a normal distribution of beak size centred around 9.5 mm (beak depth).
• This proved postulate 1 to be correct

Question 10

Are narrow beaks recessive?

Answer 10

Yes, because in 1978 there was a loss of small-beaked birds

Question 11

How did Rosemary and Peter Grant’s experiment prove Darwin’s second postulate to be correct?

Answer 11

• Their experiment showed that :
• Parents with small beaks tend to have offspring with shallow beaks.
• Thus, there is a large genetic component to determination of beak depth.

Question 12

Describe how Rosemary and Peter Grant’s experiment prove Darwin’s third postulate to be correct

Answer 12

• At the start of the drought, seeds were soft and small, but by the end of the drought, the seeds got bigger and harder.
• By 1978, the population mean beak depth had increased, meaning that the change in food supply had created a selection for bigger birds with deeper stronger beaks.
• Thus, this proved Darwin’s third postulate and showed that natural selection can drive evolution.

Question 13

How have Darwin’s postulates been proven?

Answer 13

Both experimentally and observationally

Question 14

Is it true that microevolution is both a theory and a fact?

Answer 14

Yes

Question 15

Is it true that many mutations have a little effect on ‘fitness’ and so they can’t be acted upon by natural selection?

Answer 15

Yes

Question 16

A dominant advantageous allele…

Answer 16

is ‘visible’ to natural selection as both heterozygote Aa and after the first generation, homozygote AA: it rapidly rises in frequency in the population.

Question 17

A recessive advantageous allele..

Answer 17

is only ‘visible’ to natural selection as homozygotes, and these take a long time to accumulate, so fixation takes longer

Question 18

What does natural selection do to favourable alleles in a population?

Answer 18

natural selection will tend to ‘fix’ favourable alleles in a population.

Question 19

On the top strand, how is dna read?

Answer 19

from left to right

Question 20

On the top strand, how is dna read?

Answer 20

from right to left

Question 21

Is DNA always read from 5’ to 3’?

Answer 21

Yes

Question 22

Do mutations in introns have an effect or not?

Answer 22

Mostly not, as they’re not selected for or against

Question 23

Do mutaions between genes have an effect?

Answer 23

Mostly not

Question 24

Some mutaions in genes have no effect

Question 25

Is it true that the frequencies of mutations can change in populations even in the absence of natural selection?

Answer 25

Yes

Question 26

Who tested genetic drifts affect on evolution experimentally?

Answer 26

Richard Lenski

Question 27

Describe Richard Lenski’s experiment

Answer 27

• He filled 2 flasks with E coli. One had the sugar Arabanose, the other one didn’t. He grew them over night.
• He innoculated the flasks, diluted them, and grew them in a medium with glucose and citrate.
• He grew them over night, diluted them, and grew them again and again and again.
• This experiment has been running for over 35 years

Question 28

What was the timeline and findings of Richard Lenski’s experiment?

Answer 28

• In all flasks: growth rate increased and cell size increased
• In some flasks, defects in DNA repair evolved, giving ‘mutator’ phenotypes with elevated mutation rates: these can therefore evolve more rapidly
• In one flask, Ara-3, the ability to use citrate as a carbon source in aerobic conditions evolved
• Ara-3 evolved a mutator phenotype.
• Loss of Cit+ by genetic drift, even though they had a selective advantage: sampling error. Cit+ has not re-evolved to date

Question 29

What now gives the CIt + strain of E coli a selective advantage?

Answer 29

• Cit+ strains can now utilise citrate as well as glucose as C and energy sources (read further)

Question 30

How was the Cit+ lost?

Answer 30

By genetic drift. even though they had a selective advantage: sampling error. Cit+ has not re-evolved to date

Question 31

What is a defining feature of E coli?

Answer 31

inability to utilise citrate in aerobic conditions (separating it diagnostically from pathogenic Salmonella species)

Question 32

What is gene flow?

Answer 32

The movement of alleles between previously separate populations.

Question 33

How can alleles move through the process of gene flow?

Answer 33

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

Answer 34

• Genetic drift removes genetic variation within demes (sub-populations) but leads to differentiation between demes, all by random changes in allele frequencies.
• ② Gene flow introduces new alleles into demes within a metapopulation and by itself can lead to genetic homogeneity between demes.
• If any of the demes becomes reproductively isolated, then it’s easy for natural selection to work upon it.
• combination of gene flow, genetic drift and selection promotes population divergence and can lead to speciation

Question 35

What is a species?

Answer 35

At eukaryotic level: a population of organisms that can potentially or actually interbreed, giving viable fertile offspring. Reproductively isolated

Question 36

Why are the tree frogs Hyla chrysocelis and H. versicolor not a good example of separate species?

Answer 36

• Because recent studies indicate occasional gene exchange

Question 37

Is the tube mosquito a good example of 2 separate species?

Answer 37

Yes

Question 38

Describe the Culex pipiens pipiens mosquito

Answer 38

• a bird-biting mosquito
• Females need a blood meal before laying eggs
• Breed seasonally
• Swarm
• Lay eggs in open spaces
• Inactive over winter

Question 39

Describe the Culex molestus mosquito

Answer 39

• a mammal-biting mosquito
• Females can lay eggs without a blood meal
• Breed continuously
• Do not swarm
• Lay eggs in enclosed spaces
• Active during the winter.

Question 40

What is an example of macroevolution?

Answer 40

The Big bird lineage

Question 41

Is it true that a dominant advantageous allele is ‘visible’ to natural selection as both heterozygote Aa and after the first generation, homozygote AA: it rapidly rises in frequency in the population?

Answer 41

Yes

Question 42

Is it true that a recessive advantageous allele is only ‘visible’ to natural selection as homozygotes, and these take a long time to accumulate, so fixation takes longer ?

Answer 42

Yes