Chapter 18 Populations and Evolution

Question 1

What is evolution?

Answer 1

A change in allele frequency in a population

Question 2

What is a gene pool?

Answer 2

All of the alleles of all of the genes of all of the individuals of a population

Question 3

What is allelic frequency?

Answer 3

The number of times an allele occurs in the gene pool.

Question 4

Describe the process of evolution in 4 steps.

Answer 4

1. There is variation in a population due to mutation.
2. Selection pressures are applied.
3. Those with favourable characteristics survive and reproduce
4. Favourable alleles get passed on

Question 5

What does the Hardy-Weinberg principle calculate?

Answer 5

The frequency of an allele in a population.

Question 6

What 5 assumptions does the Hardy-Weinberg Principle make?

Answer 6

1. Large population
2. No genetic drift
3. No natural selection
4. No mutation
5. Random mating

Question 7

What are the two equations used to calculate HWP?

Answer 7

p + q =1
p2 +2pq + q2 = 1

Question 8

What does p represent?

Answer 8

The frequency of dominant allele.

Question 9

What does q represent?

Answer 9

The frequency of the recessive allele.

Question 10

What does 2pq represent?

Answer 10

The frequency of heterozygotes in the population.

Question 11

What can cause variation in phenotype?

Answer 11

Genetic and environmental factors

Question 12

Where does genetic variation come from?

Answer 12

1. Mutations
2. Meiosis
3. Random fertilisation of gametes.

Question 13

What are selection pressures?

Answer 13

Factors which limit the population of a species.

Question 14

Give 3 examples of selection pressures?

Answer 14

Predation

Disease

Competition

Question 15

What 3 factors does evolution by natural selection rely on?

Answer 15

1. Organisms produce more offspring than the environment can support.
2. There is genetic variety within the populations of species.
3. There are a variety of phenotypes that selection operates against.

Question 16

Why is the overproduction of offspring important in natural selection?

Answer 16

If there are more offspring than the environment can sustain, there will be intraspecific competition. the most likely to survive will be those best adapted to the environment.

Question 17

Why is variation important in natural selection?

Answer 17

Variation within a population allows for the selection pressure to change over time, and for the population to evolve and adapt to new circumstances.

Question 18

What are the three types of selection?

Answer 18

1. Stabilising
2. Directional
3. Disruptive

Question 19

Draw a graph 9with 2 lines) to represent the effect of stabilising selection.

Answer 19

Question 20

Under what conditions does stabilising selection occur?

Answer 20

Stabilising selection occurs when the environment favours those with the most common characteristic – those on the extreme dies out.

Question 21

Give 2 examples of stabilising selection.

Answer 21

Clutch size in robins.

Human birth weight.

Question 22

Draw a graph to represent directional selection.

Answer 22

Question 23

Under what conditions does directional selection occur?

Answer 23

Directional selection occurs when the environment favours those individuals with characteristics on one of the extremes.

Question 24

Give 2 examples of directional selection.

Answer 24

Colour in peppered moths.

Neck length in giraffes.

Question 25

Draw a graph to represent disruptive selection.

Answer 25

Question 26

Under what conditions does disruptive selection occur?

Answer 26

Disruptive selection can occur when the environment changes between both extreme conditions hence, individuals on both extremes are favoured at different times and increase in number. This is the least common type of selection.

Question 27

Give 2 examples of disruptive selection.

Answer 27

Colouration in african swallowtail butterflies.

Shell colour in limpets.

Question 28

What is speciation?

Answer 28

Speciation is the evolution of a new species from existing ones.

Question 29

What is a species?

Answer 29

A group of individuals with a shared ancestry, share the same genes, but different alleles and are able to breed to produce fertile offspring. They are reproductively isolated from other species.

Question 30

What are the stages in speciation?

Answer 30

I’M a New Species!
Isolation - populations are separated by an isolating mechanism so they cannot interbreed. There is no gene flow.
Mutation - different mutations accumulate in the 2 populations leading to variation
Natural Selection - natural selection acts on the populations with different selection pressures

Eventually the 2 populations become sufficiently genetically different so that when placed together they are unable to interbreed to produce fertile offspring and a new species is formed.

Question 31

What is gene flow?

Answer 31

Gene flow is the movement of genes from one population to another.
If there is a barrier to gene flow then genetic differences between populations can accumulate.

Question 32

Name the two types of speciation.

Answer 32

Allopatric and sympatric.

Question 33

What are the isolating mechanisms that result in allopatric speciation?

Answer 33

Allopatric speciation results from geographical isolating mechanisms such as:
Mountain ranges

Rivers

Oceans

Deserts

Question 34

What are 4 isolating mechanisms that result in sympatric speciation?

Answer 34

Sympatric speciation happens in the same geographical location.
Sympatric speciation can be caused by:
1. Ecological isolation

2. Mechanical isolation
3. Behavioural isolation
4. Temporal isolation

Question 35

What is ecological isolation?

Answer 35

The populations inhabit different niches within the same habitat so do not meet to breed.

Question 36

What is mechanical isolation?

Answer 36

During mechanical isolation the populations are in the same habitat but are physically incompatible so cannot interbreed.

Question 37

What is behavioural isolation?

Answer 37

Differences in behaviour prevent breeding. Examples include:
Differences in song to attract mates.

Differences in mating displays.

Question 38

What is temporal isolation?

Answer 38

Temporal isolation occurs when the populations live in the same habitat but their breeding times do not overlap.

Question 39

What are the 2 mechanisms that prevent 2 individuals from producing fertile offspring?

Answer 39

The inability to produce fertile offspring is caused by:
Gametic Isolation

Hybrid sterility

Question 40

What is genetic isolation?

Answer 40

The gametes are unable to fuse due to genetic or biochemical incompatibility.

Question 41

Give 3 causes of gametic isolation.

Answer 41

Gametic isolation could be due to:
Sperm being unable to survive in the reproductive system of the female.

Enzymes on the sperm being unable to react with the egg to allow entry.

Pollen being unable to create a pollen tube.

Question 42

What is hybrid sterility?

Answer 42

Hybrids are often sterile due to an inability of chromosomes to pair up during meiosis.
Genes cannot be passed on.

Question 43

What is adaptive radiation?

Answer 43

Adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, creates new challenges, or opens new environmental niches.

Question 44

What is genetic drift?

Answer 44

Genetic drift is the process of random changes in allele frequency due to a chance event. It affects small, isolated populations.

Question 45

Why does genetic drift affect small isolated populations more?

Answer 45

Genetic drift has a greater impact in small, isolated populations, as alleles are more likely to be lost from the gene pool. It can lead to the random loss of rare alleles, reducing the genetic diversity of a population.

Question 46

What is the bottleneck effect?

Answer 46

Genetic bottlenecks occur when a small number of individuals are the only contributors to future generations. This can happen when most of the population dies out.

Question 47

What is the founder effect?

Answer 47

The founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population.