7.3 Evolution & Speciation

Question 1

What 3 genetic factors contribute to variation within a population?

Answer 1

Mutation
Meiosis (independent assortment & crossing over)
Random fertilisation of gametes

Question 2

In general, phenotypic variation is explained by…

Answer 2

a combination of genetic and environmental factors

Question 3

What is the primary source of genetic variation?

Answer 3

Mutation - produces new ALLELES

Question 4

What is the difference between natural selection and evolution?

Answer 4

Natural selection is the PROCESS that drives evolution

Question 5

What does natural selection change within a population?

Answer 5

ALLELE FREQUENCY!
This in turn changes the gene pool

Question 6

Natural selection depends on which 5 factors?

Answer 6

1. Organisms produce more offspring than can be supported by available resources: this leads to inTRAspecific competition
2. Genetic variation (different alleles) within population
3. Genetic variation leads to different phenotypes, which may be advantageous or disadvantageous
4. Predation
5. Disease

Question 7

Terminology for maximum population that can be supported?

Answer 7

Carrying capacity

Question 8

Define selection pressure

Answer 8

The biotic/abiotic (usually environmental so abiotic) factors that limit the size of a population

Question 9

Define gene pool

Answer 9

ALL ALLELES of a gene present in a PARTICULAR POPULATION at a PARTICULAR TIME

Question 10

Define allele frequency

Answer 10

How frequently an allele occurs in a population

Question 11

What are some example of factors limiting an individual’s chance of survival?

Answer 11

1. Competition for food
2. Competition for a reproductive mate
3. Water supply
4. Temperature
5. Predators

Question 12

What is stabilising selection?

Answer 12

Natural selection that keeps allele frequencies relatively constant over generations.
Selects AGAINST extremes of the phenotype range.

Question 13

What is directional selection?

Answer 13

Selects for ONE EXTREME of the phenotype range.
Produces a gradual change in allele frequencies over several generations.

Question 14

What is disruptive selection?

Answer 14

Selection that maintains high frequencies of TWO DIFFERENT SETS OF ALLELES (i.e. selection AGAINST THE MEAN)
Curve looks like an M shape with humps

Question 15

Describe the process of genetic drift

Answer 15

1. Allele frequencies in a population change overtime due to CHANCE
2. In each generation, some individuals may (by chance) leave behind a few more descendants than other individuals OR a chance event reduces the gene pool
3. Alleles of these “lucky” individuals become more common in next gen
4. Genetic drift happens in all populations, but effect more marked in SMALL populations

Question 16

Allopatric speciation

Answer 16

Speciation that starts with two populations becoming GEOGRAPHICALLY ISOLATED

Question 17

Describe how allopatric speciation works

Answer 17

1. species are REPRODUCTIVELY ISOLATED so no genetic exchange can occur
2. there are DIFFERENT SELECTION PRESSURES in each environment
3. there is variation due to MUTATIONS in each population
4. advantageous ALLELES selected for & passed on to next generation
5. this leads to a CHANGE IN ALLELE FREQUENCY/GENE POOL
6. eventually the two groups cannot interbreed to produce fertile offspring

Question 18

Sympatric speciation

Answer 18

When species become reproductively isolated while STILL INHABITING THE SAME PLACE

Question 19

How does sympatric speciation work (general)?

Answer 19

There must be TWO POPULATIONS with NO GENE FLOW occurring between them

Question 20

Examples of the two populations being “split” in sympatric speciation

Answer 20

1. Ecological separation: living in different environments within the same area (eg. diff soil pH in diff areas)
2. Behavioural separation: different courtship rituals/feeding patterns

Question 21

Both allopatric and sympatric speciation rely on what occurring within individuals in populations?

Answer 21

MUTATIONS!