Evolution

Question 1

What do you say when talking about natural selection?

Answer 1

MASRCA
MUTATION leads to a new allele.
Organisms with mutation are better ADAPTED to…
They are better adapted to SURVIVE and REPRODUCE
This leads to an increase/CHANGE in the ALLELE frequency.

Question 2

What is the definition of evolution?

Answer 2

Change in inherited characteristics of a group of organisms over time

Question 3

What is the definition of natural selection?

Answer 3

Individuals with more favourable characteristics are more likely to survive and pass on those traits.

Question 4

What is evolution within a species?

Answer 4

Change in allele frequency over time - study of this is called population genetics

Question 5

What is the definition of allele frequency?

Answer 5

Number of times an allele occurs in the gene pool compared to the number of alleles for that gene

Question 6

What is the definition of gene pool?

Answer 6

The sum total of all of the alleles for all of the genes in a population

Question 7

What factors affect the size/composition of the gene pool?

Answer 7

Natural selection - directional or stabilising
Population size
Random events that reduce the size of the gene pool (genetic drift)
Immigration and emigration (gene flow)
Mutation rate
Non-random mating (sexual selection)

Question 8

What are the 3 types of selection?

Answer 8

Directional
Stabilising
Disruptive

Question 9

What is directional selection?

Answer 9

Change in environment leads to new/changed selection pressure.
Alleles for favourable trait are more likely to be passed on.
Frequency of favourable alleles increase.

Question 10

What is stabilising selection?

Answer 10

Selection against extremes

Eg robins lay 4 eggs as any more - not enough food, any less - not warm enough for survival

Question 11

What is disruptive selection?

Answer 11

2 extremes get selected

Eg bird colour, brown - not competed against as not a threat, blue - not competed against as intimidating

Question 12

What is the definition of gene flow?

Answer 12

The exchange of alleles between populations.
Increases genetic diversity.
Due to immigration/emigration

Question 13

What is the advantage to survival in having a large population?

Answer 13

Leager gene pool, more variation, greater capacity to adapt/survive.

Question 14

What are the 2 categories of factors that affect population size?

Answer 14

Density dependent factors

Density independent factors

Question 15

What are density dependent factors affecting population size?

Answer 15

Depend on population size

Eg competition, predation, parasitism, communicable disease

Question 16

What are density independent factors affecting population size?

Answer 16

Affect populations of all sizes in the same way

Eg Climate change and natural disasters

Question 17

What is genetic drift?

Answer 17

A change in allele frequency that is brought about by a random event

Question 18

What are the 2 types of genetic drift?

Answer 18

Genetic bottleneck

Founder effect

Question 19

What is a genetic bottleneck?

Answer 19

When a population is drastically reduced in size by a catastrophic event eg epidemic/earthquake.
Survival is not selected, it is by chance.
Organisms that survive may not be representative of the original population so some alleles are lost.

Question 20

What is the founder effect?

Answer 20

A small population is established by a number of isolated individuals.
The gene pool of the new population is limited to the genotypes of the founder members.
Alleles that may have been rare in the original population may quickly increase in frequency.

Question 21

Why does the founder effect occur?

Answer 21

Migration, leading to geographical separation.
OR
As a result of other separation such as religion.

Question 22

What is the Hardy-Weinberg principle?

Answer 22

The frequency of dominant and recessive alleles in a population will remain constant from generation to generation provided certain conditions are met.

Question 23

What are the conditions for the Hardy-Weinberg principle?

Answer 23

Large population
No immigration/emigration
Random mating
All genotypes have same reproductive success
No gene mutation

Question 24

What are the 2 Hardy-Weinberg principle equations?

Answer 24

P + q = 1

P² + q² + 2Pq = 1

Question 25

What does P and q mean in the Hardy-Weinberg equations?

Answer 25

P = Frequency of dominant allele
q = Frequency of recessive allele

Question 26

What P², q² and Pq mean in the Hardy-Weinberg equations??

Answer 26

P² = Homozygous dominant genotype
q² = Homozygous recessive genotype
Pq = Heterozygous genotypes

Question 27

What is a species?

Answer 27

A group of similar organisms that can reproduce to give fertile offspring

Question 28

What is speciation?

Answer 28

Development of a new species

Question 29

When does speciation occur?

Answer 29

Occurs when populations of the same species become reproductively isolated. Changes in allele frequency cause changes in phenotype that mean they can no longer breed together to produce fertile offspring.

Question 30

What is allopatric speciation?

Answer 30

Caused by geographical isolation and natural selection

Develops a new species

Question 31

When does geographical isolation occur in allopatric speciation?

Answer 31

When a physical barrier divides a population of a species eg flood, volcanic eruptions and earthquakes.
All cause barriers that can isolate some individuals from the main population.

Question 32

What happens after some individuals get geographically isolated in allopatric speciation?

Answer 32

Conditions on either side of the barrier will be slightly different eg climate

Question 33

What happens to the populations in allopatric speciation because the environment is different?

Answer 33

There are different selection pressures so different characteristics will become more common due to natural selection (talk about natural selection)

Question 34

What happens at the end of allopatric speciation?

Answer 34

Individuals from the different populations will have changed so much that they won’t be able to breed with one another to produce fertile offspring.
They will be reproductively isolated.
The 2 groups will have become separate species.

Question 35

What is reproductive isolation?

Answer 35

Occurs because the changes in the alleles and phenotypes of the 2 populations prevent them from successfully breeding together.

Question 36

What 3 changes can occur to cause reproductive isolation?

Answer 36

Seasonal changes
Mechanical changes
Behavioural changes

Question 37

What are seasonal changes that cause reproductive isolation?

Answer 37

Individuals from the same population develop different mating or flowering seasons, or become sexually active at different times of the yearqq

Question 38

What are mechanical changes that cause reproductive isolation?

Answer 38

Changes in genitalia prevent successful mating

Question 39

What are behavioural changes that cause reproductive isolation?

Answer 39

A group of individuals develop courtship rituals that aren’t attractive to the main population

Question 40

What is sympatric speciation?

Answer 40

Doesn’t require geographical isolation.
Caused by random mutations within a population, resulting in reproductive isolation, preventing members of that population breeding with other members of the species.