7.3 Evolution & Speciation

Question 1

What are the 3 reasons why genetic variation arise

Answer 1

• Mutations
• Meiosis
• Random fertilisation of gametes

Question 2

What is the main source of variation

Answer 2

Mutations

Question 3

What are the 2 types of mutations that result in genetic variation

Answer 3

• Gene point mutations
• Chromosome mutations

Question 4

What is necessary for natural selection

Answer 4

Variation

Question 5

Why is variation important

Answer 5

When the environment changes, having a wide range of genetically different individuals means that there is more likely to be an individual that will be able to survive in the new environment

Question 6

What are the 2 types of variation

Answer 6

• Discontinuous
• Continuous

Question 7

What are the phenotypes like in discontinuous variation

Answer 7

Qualilative phenotypes

Question 8

What are the phenotypes like for continuous variation

Answer 8

Quantitative phenotypes

Question 9

How many genes tend to control the discontinuous variation phenotypes

Answer 9

1 or 2 with multiple alleles

Question 10

How many genes tend to control the continuous variation phenotypes

Answer 10

Many genes - polygenic

Question 11

How much does the environment effect discontinuous variation

Answer 11

Very little effect on gene expression

Question 12

How much does the environment effect continuous variation

Answer 12

Significant effect on gene expression

Question 13

Name an example of discontinuous variation

Answer 13

Human ABO blood group / this is a distinct group so you cannot be a bit of both you’re one or the other

Question 14

Name an example of continuous variation

Answer 14

Height, skin colour / graduation of characterisitics

Question 15

Is genetic variation or environmental factors more likely to be discontinuous variation

Answer 15

Genetic variation

Question 16

Are environmental variation subject to natural selection

Answer 16

NO

Question 17

Define genetic diversity

Answer 17

The total number of different alleles in a population

Question 18

Define population

Answer 18

A group of individuals of the same species that live in the same place and can interbreed

Question 19

What 3 things increase genetic diversity between populations

Answer 19

• Natural selection
• Genetic drift
• Mutations

Question 20

What 1 thing decrease the genetic diversity between populations

Answer 20

Gene flow

Question 21

What 2 things increase the genetic diversity within populations

Answer 21

• Gene flow
• Mutations

Question 22

What 3 things decrease the genetic diversity within populations

Answer 22

• Natural selection
• Genetic drift
• Inbreeding

Question 23

Why does natural selection increase genetic diversity between populations

Answer 23

Each population will experience different environment for example sunlight, so there’s a wide variety of alleles in the gene pool

Question 24

Why do mutations increase genetic diversity both between populations and within populations

Answer 24

Because they introduce new alleles so more alleles in gene pool therefore increases genetic diversity

Question 25

Why does natural selection decrease genetic diversity within populations

Answer 25

Since the individuals with the favourable characteristics reproduce more therefore there is less variation

Question 26

Why does inbreeding decrease the genetic diversity

Answer 26

No new alleles just recombining alleles so no new alleles enter the gene pool

Question 27

If there's greater genetic diversity, does this increase or decrease the likelihood that an individual will survive an environmental change, and why

Answer 27

Increases because there's a wider range of alleles = wider range of characteristics = greater probability that an individual will possess a characteristic that is suited to the conditions

Question 28

What is the process of natural selection

Answer 28

- New alleles are formed by random mutations in genetic material - Many mutations are harmful, which may mean that the individual with the mutated allele dies out, or the mutation is corrected by the 'proof-reading' mechanisms of the cell. Sometimes however, an allele (or combination of alleles) gives an individual an advantage, leading to increased chance of survival and reproductive success. - These individuals then pass on their advantageous alleles to the next generation - Over many generations, the new alleles increases in frequency in the population

Question 29

Where must the mutation occur in order for it to be passed on

Answer 29

In gametes

Question 30

When measuring a given trait in individuals of a population, what does continuous variation cause

Answer 30

Normal distribution

Question 31

What are the 3 types of selection

Answer 31

- Directional - Stabilising - Disruptive

Question 32

Define directional selection

Answer 32

Selection that operates towards one extreme in a range of variation / when individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce

Question 33

What is the specs example of directional selection

Answer 33

Antibiotic resistance in bacteria

Question 34

In directional selection, what happens to the position of the mean

Answer 34

It shifts in the direction of the more favourable trait

Question 35

In directional selection, what happens to the frequency of the mean

Answer 35

It's equally common

Question 36

In directional selection, what happens to the distribution around the mean

Answer 36

It's the same - therefore the curve looks the same but just shifted to one side

Question 37

What are the general mark scheme points for this question, Why does the frequency of this trait increase in the population

Answer 37

- Trait X (state the trait) has a genetic basis - Random mutations over time = genetic variation - Explain how the trait is of an advantage ( selection pressure) and state the type of selection - Individuals with this allele are more likely to survive, reproduce, and pass on this allele to their offspring -Over many generations, the frequency of this allele increase in the population and so therefore does the trait

Question 38

Why does the frequency of antibiotic resistance increase in the bacteria population

Answer 38

- Antibiotic resistance has a genetic base - Random mutation over time = genetic variation in resistance to the antibiotic - some individuals have alleles that give them greater antibiotic resistance - When the population is exposed to the antibiotic ( selective pressure = surviving exposure to the antibiotic), bacteria with alleles that give them less resistance are killed - Resistant bacteria survive, reproduce, and pass on the allele for antibiotic resistance to their offspring - Over many generations, the frequency of this allele increases in the population and therefore so does the trait

Question 39

Define stabilising selection

Answer 39

Selection that tends to eliminate the extremes of the phenotype range within a population. It arises when environmental conditions are constant

Question 40

What is the specs example of stabilising selection

Answer 40

Human birth weights

Question 41

In stabilising selection, what happens to the position of the mean

Answer 41

It remains the same

Question 42

In stabilising selection, what happens to the frequency of the mean

Answer 42

It becomes more common

Question 43

In stabilising selection, what happens to the distribution around the mean

Answer 43

It decreases

Question 44

Explain why stabilising selection occurs for human birth weigh

Answer 44

- Human birth weight has a genetic basis - Random mutations over time = genetic variation in birth weight - Selective pressure = surviving to reproductive age. Very small babies are less likely to survive (large SA:Vol & weakened immune system) and very large babies can cause problems in child birth - Individuals with alleles for moderate birth weights are more likely to survive, reproduce, and pass on their alleles for moderate birth weight to their offspring - Over many generations, the frequency of this allele increases in the population and so therefore does the trait

Question 45

What does natural selection result in

Answer 45

Species that are better adapted to their environment

Question 46

How do behavioural adaptations increase the likelihood an organisms surviving

Answer 46

The way an organism acts that increases its chance of survival

Question 47

How do physiological adaptations increase the likelihood an organism survives

Answer 47

Processes is inside an organism's body that increases the chance of survival

Question 48

How do anatomical adaptations increase the likelihood an organism survives

Answer 48

The features of an organisms body that increases its chance of survival

Question 49

Define disruptive selection

Answer 49

Where individuals with alleles for characteristics of both extremes at either end of the range are more likely to survive and reproduce

Question 50

In disruptive selection, what happens to the position of the mean

Answer 50

It stays the same

Question 51

In disruptive selection, what happens to the frequency of the mean, and what effect does this have on the SD

Answer 51

It decreases, so a greater SD i.e a greater spread of values about the mean

Question 52

What does stabilising selection preserve

Answer 52

The average phenotype

Question 53

What does stabilising selection select against

Answer 53

The extremes

Question 54

When does stabilising selection occur

Answer 54

In stable environments

Question 55

What does directional selection favour

Answer 55

An extreme phenotype

Question 56

When does directional selection occur

Answer 56

When the environment changes

Question 57

What does disruptive selection favour

Answer 57

Either of the extreme phenotypes

Question 58

What does disruptive selection link to

Answer 58

Speciation

Question 59

When discussing natural selection, the term 'increased reproductive success' is used. Explain what it means

Answer 59

When organisms are able to survive till reproductive age and passes on alleles

Question 60

What changes in allele frequency would be expected over a long period of time when natural selection is acting on a population

Answer 60

The advantageous allele increases in frequency

Question 61

What is selection

Answer 61

Process by which an individual is selected because it's better adapted to it's environment so more likely to survive and reproduce compared to those who are not adapted

Question 62

Distinguish between directional and stabilising selection

Answer 62

Directional selection favours one of the extremes so the characteristics of the population change whereas stabilising selection favours the average phenotype so the characteristics of the population remain unchanged

Question 63

What is speciation

Answer 63

Evolution of new species from species that already exist

Question 64

What does reproductive isolation prevent

Answer 64

Gene flow

Question 65

What is allopatric isolation

Answer 65

When some kind of physical divide that causes 2 populations to separate

Question 66

Name an example of allopatric isolation

Answer 66

When sea levels rise

Question 67

Why after allopatric isolation lead to the 2 population not being able to interbreed to produce fertile offspring

Answer 67

SInce the populations face different selection pressures, and random mutations occur and an allele will be favoured so the 2 populations become genetically different over time

Question 68

What are the 4 types of sympatric isolation

Answer 68

- Behaviour - Temporal - Ecological - Mechanical

Question 69

What is mechanical isolation (type of sympatric isolation)

Answer 69

Mutations occurs which create anatomical differences (e.g. size) so reproduction is not possible

Question 70

What is ecological isolation (type of sympatric isolation)

Answer 70

When the individuals use the environment differently, so then different alleles are favoured so the mutations then change how the individuals use their habitiat

Question 71

What is behavioural isolation (type of sympatric isolation)

Answer 71

When mutations in the DNA result in individuals not being able to do the correct mating ritual - leading to reproductive isolation - no gene flow

Question 72

What are the 8 main steps in the process of speciation

Answer 72

- Reproductively isolated - No gene flow between isolated groups - Different mutations in DNA - Different groups exposed to different environments - Subject to different selection pressures - Natural selection so difference in gene pools - Differences in phenotype - No longer interbreed between the 2 groups to produce fertile offspring - Can be considered different species

Question 73

What is genetic drift

Answer 73

A chance, non-selective event significantly alters the alleles in the gene pool

Question 74

When there's genetic drift, what is survival down too

Answer 74

Chance, since there isn't a favoured phenotype

Question 75

Does genetic drift have a larger impact on small, isolated populations or on larger population

Answer 75

Small isolated populations

Question 76

In small, isolated populations, is the change to the allele frequencies altered more by genetic drift or by natural selection

Answer 76

Genetic drift

Question 77

How does genetic drift alter the alleles in the gene pool

Answer 77

- Only a few individuals survive - Unlikely that the alleles in the survivors are exactly the same as the alleles in the original population - So the alleles aren't in the same proportion

Question 78

What are the 2 types of genetic drift

Answer 78

- Bottle neck populations - Founder effect populations

Question 79

Are bottleneck populations genetically diverse or not

Answer 79

Genetically diverse

Question 80

What happens to the genetic diverse of a bottleneck population after genetic drift

Answer 80

Genetic diversity is significantly reduced

Question 81

Why does decreasing the genetic diversity of a population, decrease their chance of survival to environmental changes

Answer 81

Lower genetic diversity decreases the likelihood that any individuals has alleles that are favourabled/ advantageous to survival

Question 82

What happens in the founder effect populations of genetic drift

Answer 82

A few individuals break away from populations

Question 83

Why does the founder effect decrease genetic diversity of a population

Answer 83

A few individuals break away from population and it's unlikely that the allele frequency is in the same proportion to the original population

Question 84

Suggest how 2 species of palm tree arose by sympatric speciation ( 5 marks) : the flowering times of the 2 species is different

Answer 84

- Occurs inn the same environment - Mutations cause different flowering times ( in the question) - Reproductive isolation / no gene flow - Different alleles passed on - Disruptive selection - Eventually the different species cannot interbreed to produce fertile offspring

Question 85

What is a gene pool (1 mark)

Answer 85

The total number of alleles within a population

Question 86

Suggest and explain how allopatric speciation may have occured (4 marks)

Answer 86

- The environments have different selection pressures - Difference due to mutations - Reproductive isolated - No gene flow - Different alleles are passed on - Eventually the different species cannot interbreed to produce fertile offspring

Question 87

List all the marking points that need to be said when explaining evolution of 2 geographically isolated species

Answer 87

1. Geographical isolation/separation due to elevation/altitude ( or whatever it's due to) 2. Allopatric speciation due to isolation/separation; 3. Different selection pressures OR Different environment(s); 4. (However) some overlap in distribution OR (Both) plants found in same area/habitat/altitude; 5. So (possibly) sympatric speciation; 6. (Variation due to) mutation(s); 7. Reproductive isolation/separation due to different pollinators/distributions/altitudes OR Separate gene pools due to different pollinators/distributions/altitudes; 8. Change in allele frequency (in each population) OR Different allele frequency (in each population); 9. Different species) can no longer (interbreed to) produce fertile offspring;

Question 88

Guppies with large brains are better at identifying predators. The scientist found that only female guppies with large brains were attracted to male guppies bright in colour. Suggest and explain the advantage of this behaviour to the population of guppies (3 marks)

Answer 88

1. (Females with large brains) will mate with males bright in colour; Accept answers that include references to alleles 2. Their (male) offspring would be (more likely to be) bright in colour; 3. (Bright in colour male) offspring could attract larger brained females; 4. The population/offspring could (evolve to) have larger brains; Ignore answers relating to females only 5. The population/offspring are better at identifying/avoiding predators;

Question 89

Describe how the behaviour of female guppies could result in sympatric speciation (3 marks)

Answer 89

1. Not geographically isolated; Accept are in the same area 2. (Leading to) reproductive isolation OR Gene pools kept separate; 3. Changes in allele frequencies; Reject gene frequencies 4. Cannot breed/mate to produce fertile offspring;

Question 90

Describe how farming cattle as a source of milk could have led to an increase in LP (lactase persistant so individuals have enzyme lactose that hydrolyses lactose) (4 marks)

Answer 90

1. LP due to mutation OR Allele due to mutation; Reject mutation caused by drinking milk. Reject (LP) gene 2. Milk provides named nutrient; Accept any correct named nutrient e.g. glucose, galactose, protein Ignore ‘sugar’ ‘lactose’ as named nutrient 3. Individuals with LP more likely to survive and reproduce OR Individuals with advantageous allele more likely to survive and reproduce; Reject (LP) gene Accept ‘individuals who produce lactase’ for ‘LP individuals’ Accept ‘pass on allele/LP/characteristic’ for reproduce. 4. Directional selection; 5. Frequency of allele increases (in the offspring/next generation);

Question 91

Lord Howe Island in the Tasman Sea possesses 2 species of palm tree which has arisen via sympatric speciation. The 2 species derived from each other after the island was formed 6.5 million years ago. The flowering times of the 2 species are different. Suggest how these 2 species of palm tree arose by sympatric speciation (5 marks)

Answer 91

1. Occurs in the same habitat / environment / population; 2. Mutation/s cause different flowering times; 3. Reproductive separation / isolation OR No gene flow OR Gene pools remain separate; 4. Different allele/s passed on / selected OR Change in frequency of allele/s 5. Disruptive (natural) selection; 6. Eventually different species cannot (inter)breed to produce fertile offspring;

Question 92

One farmer stated that the increase in the use of Bt crop plants had causes a mutation in one of the insect species and that this mutation had spread to other species of insect. Was he correct? Explain your answer (4 marks)

Answer 92

(No – no mark) 1. Mutations are spontaneous / random; 2. Only the rate of mutation is affected by environment; 3. Different species do not interbreed / do not produce fertile offspring; 4. So mutation / gene / allele cannot be passed from one species to another

Question 93

There was a time lag between the introduction of Bt crops and the appearance of the first insect species that was resistant to the Bt toxin, explain why (3 marks)

Answer 93

1. Initially one / few insects with favourable mutation / allele; 2. Individuals with (favourable) mutation / allele will have more offspring; 3. Takes many generations for (favourable) mutation / allele to become the most common allele (of this gene).

Question 94

There are 9 subspecies of giraffe. These subspecies evolved when populations of giraffe were separated from long time periods. Each subspecies has distinct coloured skin markings. Some biologists have suggested that up to six of these subspecies shoudl be classified as different species. Explain how different subspecies of giraffe may have evolved from a common ancestor (5 marks)

Answer 94

1. No interbreeding / gene pools are separate / geographic(al) isolation; Accept: reproductive isolation as an alternative to no interbreeding. 2. Mutation linked to (different) markings/colours; 3. Selection/survival linked to (different) markings/colours; 4. Adapted organisms breed / differential reproductive success; Note: ’passed on to offspring’ on its own is not sufficient for reproduction. 5. Change/increase in allele frequency/frequencies;

Question 95

Biologists compared the mitochondrial DNA of the different subspecies of giraffe. They used the results from comparing this DNA to conclude that 6 of the 9 subspecies are separate species, suggest how they came to this conclusion (2 marks)

Answer 95

1. (Compare DNA) base sequence / base pairing / (DNA) hybridisation; Ignore: compare chromosomes / ‘genetic make-up’. Accept: (compare) genes / introns / exons. Note: reference to only comparing alleles is 1 max. 2. Different in six (species) /different in different species / similar in three (subspecies) /similar in same species/subspecies;