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AQA A level Biology > 7.3 Evolution & Speciation > Flashcards

7.3 Evolution & Speciation Flashcards

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1
Q

What are the 3 reasons why genetic variation arise

A
  • Mutations
  • Meiosis
  • Random fertilisation of gametes
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2
Q

What is the main source of variation

A

Mutations

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3
Q

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

A
  • Gene point mutations
  • Chromosome mutations
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4
Q

What is necessary for natural selection

A

Variation

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5
Q

Why is variation important

A

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

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6
Q

What are the 2 types of variation

A
  • Discontinuous
  • Continuous
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7
Q

What are the phenotypes like in discontinuous variation

A

Qualilative phenotypes

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8
Q

What are the phenotypes like for continuous variation

A

Quantitative phenotypes

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9
Q

How many genes tend to control the discontinuous variation phenotypes

A

1 or 2 with multiple alleles

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10
Q

How many genes tend to control the continuous variation phenotypes

A

Many genes - polygenic

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11
Q

How much does the environment effect discontinuous variation

A

Very little effect on gene expression

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12
Q

How much does the environment effect continuous variation

A

Significant effect on gene expression

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13
Q

Name an example of discontinuous variation

A

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

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14
Q

Name an example of continuous variation

A

Height, skin colour / graduation of characterisitics

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15
Q

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

A

Genetic variation

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16
Q

Are environmental variation subject to natural selection

A

NO

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17
Q

Define genetic diversity

A

The total number of different alleles in a population

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18
Q

Define population

A

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

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19
Q

What 3 things increase genetic diversity between populations

A
  • Natural selection
  • Genetic drift
  • Mutations
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20
Q

What 1 thing decrease the genetic diversity between populations

A

Gene flow

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21
Q

What 2 things increase the genetic diversity within populations

A
  • Gene flow
  • Mutations
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22
Q

What 3 things decrease the genetic diversity within populations

A
  • Natural selection
  • Genetic drift
  • Inbreeding
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23
Q

Why does natural selection increase genetic diversity between populations

A

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

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24
Q

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

A

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

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25
Q

Why does natural selection decrease genetic diversity within populations

A

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

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26
Q

Why does inbreeding decrease the genetic diversity

A

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

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27
Q

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

A

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

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28
Q

What is the process of natural selection

A
  • 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
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29
Q

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

A

In gametes

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30
Q

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

A

Normal distribution

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31
Q

What are the 3 types of selection

A
  • Directional
  • Stabilising
  • Disruptive
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32
Q

Define directional selection

A

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

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33
Q

What is the specs example of directional selection

A

Antibiotic resistance in bacteria

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34
Q

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

A

It shifts in the direction of the more favourable trait

35
Q

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

A

It’s equally common

36
Q

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

A

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

37
Q

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

A
  • 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
38
Q

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

A
  • 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
39
Q

Define stabilising selection

A

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

40
Q

What is the specs example of stabilising selection

A

Human birth weights

41
Q

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

A

It remains the same

42
Q

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

A

It becomes more common

43
Q

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

A

It decreases

44
Q

Explain why stabilising selection occurs for human birth weigh

A
  • 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
45
Q

What does natural selection result in

A

Species that are better adapted to their environment

46
Q

How do behavioural adaptations increase the likelihood an organisms surviving

A

The way an organism acts that increases its chance of survival

47
Q

How do physiological adaptations increase the likelihood an organism survives

A

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

48
Q

How do anatomical adaptations increase the likelihood an organism survives

A

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

49
Q

Define disruptive selection

A

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

50
Q

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

A

It stays the same

51
Q

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

A

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

52
Q

What does stabilising selection preserve

A

The average phenotype

53
Q

What does stabilising selection select against

A

The extremes

54
Q

When does stabilising selection occur

A

In stable environments

55
Q

What does directional selection favour

A

An extreme phenotype

56
Q

When does directional selection occur

A

When the environment changes

57
Q

What does disruptive selection favour

A

Either of the extreme phenotypes

58
Q

What does disruptive selection link to

A

Speciation

59
Q

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

A

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

60
Q

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

A

The advantageous allele increases in frequency

61
Q

What is selection

A

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

62
Q

Distinguish between directional and stabilising selection

A

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

63
Q

What is speciation

A

Evolution of new species from species that already exist

64
Q

What does reproductive isolation prevent

A

Gene flow

65
Q

What is allopatric isolation

A

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

66
Q

Name an example of allopatric isolation

A

When sea levels rise

67
Q

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

A

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

68
Q

What are the 4 types of sympatric isolation

A
  • Behaviour
  • Temporal
  • Ecological
  • Mechanical
69
Q

What is mechanical isolation (type of sympatric isolation)

A

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

70
Q

What is ecological isolation (type of sympatric isolation)

A

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

71
Q

What is behavioural isolation (type of sympatric isolation)

A

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

72
Q

What are the 8 main steps in the process of speciation

A
  • 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
73
Q

What is genetic drift

A

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

74
Q

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

A

Chance, since there isn’t a favoured phenotype

75
Q

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

A

Small isolated populations

76
Q

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

A

Genetic drift

77
Q

How does genetic drift alter the alleles in the gene pool

A
  • 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
78
Q

What are the 2 types of genetic drift

A
  • Bottle neck populations
  • Founder effect populations
79
Q

Are bottleneck populations genetically diverse or not

A

Genetically diverse

80
Q

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

A

Genetic diversity is significantly reduced

81
Q

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

A

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

82
Q

What happens in the founder effect populations of genetic drift

A

A few individuals break away from populations

83
Q

Why does the founder effect decrease genetic diversity of a population

A

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

AQA A level Biology (32 decks)

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