Selection, Gene Flow and Mutation

Question 1

What level does selection occur at?

Answer 1

the phenotypic level

Question 2

If an allele is dominant what would the fitness be of the heterozygote?

Answer 2

it would be the same as the dominant homozygote

Question 3

If an allele is recessive what would the fitness be of the heterozygote?

Answer 3

it would be the same as the recessive homozygote

Question 4

Name the types of selection (5)

Answer 4

1. Directional
2. Disruptive
3. Stabilising
4. Balancing
5. Fluctuating

Question 5

Describe directional selection

Answer 5

one allele is favoured over the other

Question 6

Describe disruptive selection

Answer 6

extremes of a trait are favoured

Question 7

Describe stabilising selection

Answer 7

variation is reduced

Question 8

Describe balancing selection

Answer 8

large amounts of alleles are present in a population

Question 9

Describe fluctuating selection

Answer 9

the direction of selection changes overtime

Question 10

What type of selection is being shown in this graph?

Answer 10

balancing selection

Question 11

What type of selection is being shown in this graph?

Answer 11

disruptive selection

Question 12

What type of selection is being shown in this graph?

Answer 12

directional selection

Question 13

What type of selection is being shown in this graph?

Answer 13

stabilising selection

Question 14

What does the line of best fit represent in an evolutionary graph?

Answer 14

selection

Question 15

What is always happening in the background?

Answer 15

drift

Question 16

Why can it hard to eradicate a recessive trait?

Answer 16

• heterozygote fitness is equal to homozygous dominant
• there will be no fixation
• recessive allele can hide in the heterozygote

Question 17

Give an example of a recessive disease

Answer 17

Ellis-van Creveld syndrome

Question 18

Why is it easier to eradicate a dominant disease?

Answer 18

• heterozygote fitness is equal to homozygous dominant
• there will be fixation
• recessive allele cannot hide in the heterozygote
• the only genotype selected for will be the recessive homozygote

Question 19

Give an example of a dominant disease

Answer 19

Marfan syndrome

Question 20

What is overdominance?

Answer 20

the heterozygote has the greatest fitness and is therefore preferred

Question 21

What is underdominance?

Answer 21

the heterozygote has the lowest fitness and is therefore not preferred

Question 22

What will the allele frequency be under overdominace/heterozygote advantage?

Answer 22

at equilibrium because in a heterozygote there are two alleles so if you had a high allele frequency of one allele then it is more likely it would be present in homozygotes which is not preferred

Question 23

When would there be fixation in overdominance/ heterozygote advantage?

Answer 23

if the original allele frequency was at fiaxtion, so there is only homozygotes present

Question 24

How would you change the point of equilibrium in overdominance/ heterozygote advantage?

Answer 24

by changing the fitness levels of the homozygotes

Question 25

What would the allele frequencies be like in underdominance/ heterozygote disadvantage?

Answer 25

common (fit) alleles are driven to fixation rare (unfit) alleles are driven out of the population this is because if there are two alleles then they can exist as heterozygotes which is selected against

Question 26

Can you reach equilibrium in underdominance /heterozygote disadvantage?

Answer 26

yes but it is very unstable

Question 27

What would happen if new mutations arised in underdominance/ heterozygote disadvantage?

Answer 27

they would almost immediately be wiped out

Question 28

What is frequency dependent selection?

Answer 28

a type of selection where rare alleles are favoured

Question 29

Describe frequency dependent selection

Answer 29

rare allele is favoured until it is not rare anymore due to an increase in the allele frequency of those alleles, after this the other allele, which is now rare, will be favoured

Question 30

Give an example of frequency dependent selection

Answer 30

batesian mimicry

Question 31

Describe batesian mimicry

Answer 31

when an edible organism mimics a poisonous one

Question 32

Explain why batesian mimicry is an example of frequency dependent selection

Answer 32

* predators will believe mimic is poisonous so won't eat it * the mimic is selected for * mimic populations will increase * eventually there will be too many mimics so predators will try eating them * the mimic is no longer selected for * the non-mimic population will increase * the cycle will repeat

Question 33

What is meant by gene flow?

Answer 33

the process by which alleles are moved from one population to another

Question 34

_True or False_ The movement of individuals always means the movement in genes Give an explanation why

Answer 34

False because the moving individual may not be able to breed with the other populations so the genes will not be transfered to offspring

Question 35

_True or False_ Gene flow can only be one-dimensional Give a reason why

Answer 35

False it can be both multi-dimensional and one-dimensional

Question 36

What will happen if there is no gene flow?

Answer 36

populations will become genetically differentiated from each other

Question 37

What does it mean if populations homogenise?

Answer 37

individuals within the population become very similar, almost like they are 1

Question 38

What can gene flow cause?

Answer 38

lost genetic variation in a population

Question 39

What do mutations cause?

Answer 39

the production of genetic variation

Question 40

What do most cases of mutation cause?

Answer 40

no effect or very slight change

Question 41

_True of False_ Mutations can improve an organisms chance of survival Explain your answer

Answer 41

True some mutations can improve an organisms fitness so it will will have an increased chance of survival

Question 42

Name the small scale mutations that can occur (4)

Answer 42

* point mutation * insertion * deletion * frame shift

Question 43

Explain what frame shift is

Answer 43

a change in the amino acid sequence this applies to insertion and deletion events

Question 44

Explain what point mutation is

Answer 44

one base is swapped for another

Question 45

Give an example of a disease that is caused by the following small scale mutation: point mutation

Answer 45

sickle cell anaemia

Question 46

Give an example of a disease that is caused by the following small scale mutation: insertion

Answer 46

huntingtons disease

Question 47

Give an example of a disease that is caused by the following small scale mutation: deletion

Answer 47

Duchenne muscular dystrophy

Question 48

Give an example of a disease that is caused by the following small scale mutation: frame shift

Answer 48

Chrohn's disease this is currently being debated

Question 49

Name the large scale mutations that can occur (6)

Answer 49

* ​large scale insertion * large scale deletion * inversion * duplication * insertion from another chromosome * translocation

Question 50

Describe what is meant by translocation

Answer 50

swapping of sections of chromosomes between chromosomes

Question 51

What is polysomy?

Answer 51

there is an extra copy of a chromosome

Question 52

Give an example of a disease caused by polysomy and name the chromosome it effects

Answer 52

Down's Syndrome there is an extra copy of the chromosome 21

Question 53

What type of very large scale duplication is used in the agricultural industry?

Answer 53

whole genome duplication

Question 54

Why can whole genome duplication be a good thing?

Answer 54

it yields larger fruits/crops

Question 55

Give an example of whole genome duplication

Answer 55

wheat

Question 56

What is the downside to using whole genome duplication in crops?

Answer 56

there is a large amount of 'spare' DNA which is more likely to mutate

Question 57

What is the effect of changing population sizes on the rate of mutation?

Answer 57

no change the rate of mutation is independent of the size of a population

Question 58

What can mutation cause?

Answer 58

the re-introduction of lost genetic information

Question 59

What does mutation induce?

Answer 59

genetic variation