The origin of species, Lecture 7

Question 1

Evolution requires …

Answer 1

changes in allele and genotype frequency (microevolution)

Question 2

Four evolutionary forces which cause changes in allele and genotype frequency?

Answer 2

1. mutation
2. gene flow
3. genetic drift
4. natural selection

Question 3

Mutation
(evolutionary forces which cause changes in allele and genotype frequency)
4 points

Answer 3

• changes in genetic code
• more important if occurs in cells that produce gametes
• current organism likely to be well adapted to environment, therefore more likely to be detrimental than beneficial
• generally low rates, small effects on large populations

Question 4

Gene flow
(evolutionary forces which cause changes in allele and genotype frequency)
2 points

Answer 4

• gene pool
• movement of genes between populations, eg: genetic exchange due to migration of fertile individuals or gametes between populations

Question 5

Gene pool

Answer 5

All the alleles in a population are known as the gene pool

Question 6

Genetic drift
(evolutionary forces which cause changes in allele and genotype frequency)
definition

Answer 6

chance alterations in population’s allele frequencies

Question 7

Causes of genetic drift
(evolutionary forces which cause changes in allele and genotype frequency)
2

Answer 7

1. bottlenecks

2. founder effects

Question 8

Causes of genetic drift
(evolutionary forces which cause changes in allele and genotype frequency)
bottlenecks

Answer 8

• size of population is severely reduced

- reduces variation

Question 9

Causes of genetic drift
(evolutionary forces which cause changes in allele and genotype frequency)
Example of bottlenecks

Answer 9

Northern elephant seal,
hunted by humans in the 19th century (1800s)
population reduced to 20-30 individuals
now 100,000 individuals

Question 10

Causes of genetic drift
(evolutionary forces which cause changes in allele and genotype frequency)
Founder effects

Answer 10

one/few individuals of a species become founders of a new isolated population
rare alleles in old population, may become significant in new population:
- could be detrimental
- reduced genetic variation
- non-random distribution of genes

Question 11

Causes of genetic drift
(evolutionary forces which cause changes in allele and genotype frequency)
Example of founder effects

Answer 11

Galapagos islands

Question 12

Natural selection
(evolutionary forces which cause changes in allele and genotype frequency)

Answer 12

Differential success in reproduction, i.e. some variants leaving more offspring

Question 13

Three factors which drive natural selection

Answer 13

1. climate
2. avoidance of predators
3. resistance to pesticides

Question 14

Three types of natural selection

Answer 14

1. stabilising
2. directional
3. disruptive/diversifying

Question 15

Stabilising selection

Answer 15

both extremes are at a disadvantage

Question 16

Directional selection

Answer 16

one extreme is at a disadvantage

Question 17

Disruptive/diversifying selection

Answer 17

average individuals are at a selective disadvantage

Question 18

Carrying capacity

Answer 18

high density population

Question 19

Population growth

general trend

Answer 19

1. initial rapid growth of a low density population

2. growth rate slows, maximum population size eventually reached

Question 20

K-selection

Answer 20

(density dependent)

At high density populations, traits (adaptations) are favoured that enable reproduction with fewer resource.

Question 21

R-selection

Answer 21

(density independent)

At low density populations, selection favours traits that promote rapid reproduction.

Question 22

Speciation

Answer 22

The origination of a new species. driven by population divergence.

Question 23

Population

Answer 23

A group of individuals of the same species living in a particular geographical location

Question 24

Two types of speciation

Answer 24

allopatric

and sympatric

Question 25

Allopatric speciation

Answer 25

Population forms a new species whilst geographically separated from its parent population

Question 26

Where is allopatric speciation more likely?

Answer 26

smaller, isolated populations

Question 27

Sympatric speciation

Answer 27

Occurs in geographically overlapping populations,

new species evolve from a single ancestral species whilst in the same geographic region

Question 28

Process of allopatric speciation

3

Answer 28

1. physical separation
2. separated populations diverge
3. become productively separated (unable to interbreed/exchange genes)

Question 29

Example of allopatric speciation

Answer 29

ring species,

photo in notes

Question 30

Example of sympatric speciation

Answer 30

autopolyploidy

Question 31

Reproductive barriers

Answer 31

These ensure new species keep their separate identities

Question 32

Two types of reproductive barriers

Answer 32

prezygotic and postzygotic

Question 33

Prezygotic

reproductive barriers

Answer 33

impedes mating between species or fertilisation of ova is mating is attempted

Question 34

postzygotic

reproductive barrier

Answer 34

prevents any ovum fertilised by another species from developing into a viable fertile adult

Question 35

Reasons for prezygotic reproductive barriers

5

Answer 35

habitat isolation
behavioural isolation
temporal isolation - eg: orchids living in the same place flower on different days
mechanical isolation
gametic isolation

Question 36

Reasons for postzygotic reproductive barriers

2

Answer 36

reduced hybrid fertility eg: mule

hybrid breakdown, offspring of hybrids are feeble or sterile

Question 37

TWO RATES OF EVOLUTION

Answer 37

Gradualism

Punctuated equilibrium

Question 38

Gradualism

rates of evolution

Answer 38

gradual evolutionary change, slow but constant rate of change

Question 39

Punctuated equilibrium

rates of evolution

Answer 39

Appearance of new characteristics give rise to new species relatively rapidly and then persist unchanged for a long time (equilibrium)
new innovations result in a new spurt of evolution which would result in a ‘punctuation’ of the fossil record

Question 40

Are both rates of evolution correct?

Answer 40

yes, differs between species