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AQA A level Biology > Populations And Evolution (18) > Flashcards

Populations And Evolution (18) Flashcards

1
Q

Define gene pool

A

All the alleles of all the genes of all the individuals in a population at a given time

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2
Q

Define allele frequency

A

The number of times an allele occurs within the gene pool

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3
Q

Can every gene only have two different alleles ?

XXXX

A

Jeans can I have two or more possible animals. Individual humans have two alleles so two versions of each gene because we have this we are known as diploid organisms. The greater the number of potential alleles the more diversity in a given heritable trait

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4
Q

Cystic fibrosis alleles

A

Recessive f allele leads to production of thicker mucus

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5
Q

What do you mean by combinations of alleles ?

A

F - dominant
f - recessive

Heterozygous dominant Ff

Homozygous dominant FF

Homozygous recessive ff

heterozygous Ff

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6
Q

Bb

bb

What is the frequency of the bore allele in the population?

A

1/4

0.25

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7
Q

What is the hardy Weinberg principal?

A

Provides mathematical equation that can be used to calculate fréquence of the alleles of a particular gene in a population

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8
Q

What does the hardy Weinberg principal assume?

A

The proportion of dominant and recessive alleles of any gene in a population remains the same

from one generation to the next

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9
Q

The hardy Weinberg principal assumes that the proportion of dominant and recessive alleles of any Gene in a population will remain the same across generations.

What conditions must be met for this to remain true?

A
  • no mutations
  • population is isolated so no flow of alleles in or out of the population
  • no selection (all alleles equally likely to be passed on)
  • population is large
  • mating within population is random
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10
Q

Bb

bb

Explain allele frequencies using this

A

Frequency of b = 3/4 = 0.75 = 75%

Frequency of B = 1/4 = 0.25 = 25%

75% of genes have the b allele
25% of the genes have the B allele

p + q = 100%
p + q = 1.0
Frequency of dominant + frequency of recessive = 1

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11
Q

p

A

Frequency of dominant allele

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12
Q

q

A

Frequency of recessive allele

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13
Q

How many arrangements can you get with two alleles?

Eg. Alleles A and a

A

Eg. AA, Aa, aA, aa

FOUR

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14
Q

Where:

A = dominant (frequency of A denoted as p)

a = recessive (frequency of a denoted as q)

If there are only 4 possible arrangements of the A and a alleles, what can we state?

A

AA
Aa
aA
aa

All the frequencies of those combinations add to 1.0

AA + Aa + aA + aa = 1.0

pp + pq + qp + qq

p^2 + 2pq + q^2 = 1.0

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15
Q

A particular characteristic is as a result of a recessive allele a.

We know 1 person in 25 000 display the characteristic.

How do you determine the probability of the a allele in the population? And then the probability of heterozygous individuals and ty throw the probability of genotypes and phenotypes.

A

Character observed if individual has aa

Probability of aa is 1/25 000 = 0.00004

Probability of aa is q^2

q^2 = 0.00004 then square root of q = 0.0063

If p + q = 1, p + 0.0063 = 1 so rearrange to find p = 0.9937

So probability of allele A is 0.9937

——
Then can find probability of heterozygous individuals: 2pq so we do (2 x 0.9937 x 0.0063) = 0.0125.

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16
Q

Three things genetic variations arise as a result of

A

1) Mutations
2) meiosis - produces new combinations of alleles before passed into gametes
3) random fertilisation of gametes - produces new combinations of alleles. Which gamete fuses with which is a random process at fertilisation.

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17
Q

Intraspecific variation

A

Variation within a species

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18
Q

Interspecific variation

A

Variation across different species

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19
Q

How are genetics and environment intertwined?

A

Genes set the limits

Environment determines where along the limits an organisms lies

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20
Q

Buttercups have a gene for them to grow very tall but they are actually short, why is this?

A

The seeds germinated in an environment of poor light or low nitrates in the soil so the plant could not grow properly

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21
Q

Examples of environmental influences on genetics

A

Temperature

Rainfall

Sunlight

Soil conditions

PH

Food availability

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22
Q

Polygenic

A

Characteristics determined by multiple genes

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23
Q

Example of characteristics of organisms that great into each other forming a continuum

A

Height and mass

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24
Q

Human heights as a graph is usually

A

Normal distribution curve

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25
Q

Why are the causes of variation difficult to measure?

A

Genetics and environment intertwined

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26
Q

Define sexual reproduction

A

Fusion of female and male gametes during fertilisation to produce a combination of alleles from both parents

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27
Q

Define asexual reproduction

A

Does not involve fusion of gametes. A clone of the parent is produced.

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28
Q

Advantages of sexual reproduction (3)

A

Produces genetic variation in the offspring

A disease is less likely to affect all the individuals in a population because they are more varied

Because there’s more variation The species can adapt to new environments which gives them a survival advantage

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29
Q

Disadvantages of sexual reproduction (2)

A

Time and energy needed to find a mate

Not possible for an isolated individual to reproduce

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30
Q

Advantages of asexual reproduction (4)

A

Population can increase
Rapidly in favourable conditions

Only one parents needed

More time and energy efficient as you don’t need to mate

Faster than sexual reproduction

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31
Q

Disadvantages of asexual reproduction

A

Disease may affect all the individuals in a population because there is less variation

It does not lead to genetic variation in a population (unless by mutation)

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32
Q

Define selection pressures

A

External factors which affect an organism is ability to survive in a given environment

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33
Q

Examples of selection pressures

PFPCMDC

A

Predators - advantageous allés to escape

Food - advantageous alleles allow access to certain food

Prey - advantages alleles to catch prey better etc

Climate - advantages alleles to survive in climate better

Mates - some might have advantage alleles that attract makes more

Disease - advantageous alleles allow survival

Competition - advantageous alleles outcompete

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34
Q

Positive selection pressures

A

Increases the frequency of a trait

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35
Q

Negative selection pressures

A

Decreases the occurrence of a trait

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36
Q

What do selection pressures determine?

A

The allele frequency within a gene pool

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37
Q

Name three factors that the process of evolution by natural selection depends upon?

A

1) organisms producing more offspring than can be supported by the environment (why is this important)?
2) there is genetic variety within POPULATIONS of all species
3) a variety of phenotypes that selection can operate against

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38
Q

Explain the role of over production of offspring in natural selection.

A

Too many offspring results in intraspecific competition over limited resources available

Larger population more competition and more individuals die trying to survive

Death NOT random. Those less well adapted to prevailing conditions die and those who ARE adapted survive.

Those with advantageous alleles survive and reproduce and pass the alleles to the next generation so this new generation has a different allele frequency compared to the one before.

Population has evolved a combination of alleles better adapted to the prevailing conditions.

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39
Q

What does natural selection as a result of overproduction of offspring rely on?

A

Genetically different individuals in the population.

(Then some will be better at feeding for example and some will die out etc otherwise nobody clearly wins during competition for resources etc)

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40
Q

How does allele frequency change across generations of populations?

A

Generation 1 has range of alleles and some are selected for so these in individuals survive and reproduce to have offspring with more combinations of these advantageous alleles

Generation 2 now has more combinations of these advantageous alleles

41
Q

If an organism can survive In the conditions which it’s lives in, why does it not produce identical offspring, as they will be equally likely to be able to survive in these conditions as well.

A

Conditions change over time and having a wide range of genetically different individuals in a population means that some will have a combination of alleles needed to survive in almost any new circumstance

42
Q

Why is little genetic diversity within a population BAD?

A

Populations with little individual genetic variation a more vulnerable to disease and climate change.

43
Q

Why is variation among individuals important in a population?

A

Provides the potential for a population to evolve and adapt to new circumstances

44
Q

How does a larger population lead to more genetic variation?

XXX

A

The larger population the more genetically varied it is.

So the larger combination of alleles produced when individuals in the population mate.

So larger chance of at least some of these combinations being advantageous

So selected for and individuals can survive and reproduce

(Ig population hasn’t been that large then perhaps correct combination of alleles to produce advantageous allele would have been made so none can survive and reproduce so those individuals die out ??)

45
Q

What actually is genetic variation within a species?

A

All of the individuals in the population have the same genes her that they have different alleles

46
Q

How does meiosis cause genetic variation?

A

Crossing over of chromatids

Independent segregation of chromosomes

Random fertilisation of gametes during sexual reproduction

47
Q

What causes evolution

A

Genetic variation

48
Q

What is evolution in terms of genetics

A

Changes in allele frequencies overtime

49
Q

Describe stabilising selection

A

Individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce.

50
Q

When does stabilising selection occur?

A

When the environment isn’t changing

51
Q

What does stabilising selection do?

A

Reduces the range of possible phenotypes

52
Q

Give an example of stabilising selection?

A

In a mammal population there is a range of fur lengths

In a stable climate having for at extremes of the range reduces the chances of surviving because it is hard to maintain body temperature.

Animals with alleles for average for length are more likely to survive and reproduce, passing on these advantageous alleles to the next generation.

So these alleles for medium length for increase in frequency.

Proportion of the population with average for lunch increases and the range of fur lengths decrease.

53
Q

Describe directional selection.

A

Where individuals with alleles for a single extreme phenotype are more likely to survive and reproduce

54
Q

When might directional selection occur?

A

In response to an environmental change

55
Q

Give an example of directional selection?

A

The speed of cheaters developing through directional selection.

Individuals with alleles for increase speed are more likely to catch prey and slow individuals.

These individuals were more likely to survive reproduce and pass on the advantageous alleles.

Over time frequency of alleles for high speed increases and the population becomes faster

56
Q

What is disruptive selection?

A

Where individuals with alleles for extreme phenotypes at either end of the range are more likely to survive and reproduce

57
Q

What is disruptive selection the opposite of and how?

A

Stabilising selection.

In disruptive selection characteristics towards the middle of the range are lost where is in stabilising selection characteristics towards the middle of the range are selected for

58
Q

When does disruptive selection occur?

A

When the environment favours more than one phenotype

59
Q

Give an example of disruptive selection.

A

Bird populations have a range of beak sizes.

But with large beaks can eat large seeds, but with small beaks can eat small beads.

In an environment where majority of seats are large or small but none are medium-sized, birds with medium sized beaks have a reduced chance of survival because they can’t eat the big or small seeds.

Birds with large or small beaks are more likely to survive reproduce and pass on advantageous alleles of having small or large beaks.

Alleles for large beaks and small beaks increase in frequency whilst alleles for medium-sized beaks decrease in frequency.

Overtime proportion of the population that have either small or large beaks increases

60
Q

What is another example of stabilising selection

A

Body mass of human children at birth

Baby is born with a body mass greater or less than the 3.2 kg average have a higher risk of dying in the first few months after birth

61
Q

Directional selection is a

A

Selection for one extreme phenotype

62
Q

Stabilising selection is a

A

Selection against the extreme phenotypes

63
Q

Disruptive selection is a

A

Selection against phenotypes around the mean of the population

64
Q

Give another example of directional selection

A

Antibiotic resistance in bacteria.

Selecting for an extreme phenotype - selects for bacteria with mutation to survive antibiotic so these survive and reproduce and pass on advantageous alleles

65
Q

Give another example of disruptive selection

A

Co-ho salmon.

Large Mills and small nails have been selected for loss intermediate the size males are selected against.

Small males able to sneak up on females in spawning grounds was large males are fierce competitors and so both can survive and reproduce

66
Q

Disruptional selection is when the environment favours more than one phenotype.

When might this occur ?

A

When an environmental factor for example temperature takes two or more distinct forms.

For example if the temperature alternates between very low in winter (favour long fur length) and very high in summer (favouring short fur length)

67
Q

Define allele frequency

A

The number of times and allele occurs within the gene pool

68
Q

What do you environmental factors not do

A

They do not affect the probability of a particular mutant allele arising, they affect the frequency of the mutant allele which is already in the gene pool

69
Q

What is speciation?

A

Evolution of new species from existing ones

70
Q

Define species

A

A group of individuals that Have the same jeans but different alleles and are capable of breathing to produce fertile offspring

71
Q

Members of species are what from other species?

A

Reproductively separated

72
Q

When does speciation occur?

A

When populations of the same species become reproductively isolated

73
Q

What does it mean to become reproductively isolated

A

Changes and are you frequency cause a change in phenotype which means individuals of the same species can no longer interbreed to produce fertile offspring

74
Q

Define allopatric speciation

A

Mode of speciation that occurs when biological populations become geographically isolated from each other to an extent that prevents or interferes with gene flow

75
Q

When might allopatric speciation occur?

A

When there is a physical barrier for example flood or earthquake that divides a population of species causing some of the individuals to become separated from the main population

76
Q

Sympatric speciation

XXXXX

A

Evolution of a new species from a surviving ancestral species Well both continue to inhabit the same geographical region

Is it basically like normal speciation we learnt in GCSE so like MVARPS but carried on until a whole new species appears????

77
Q

Two ways that individuals within a population can become reproductively isolated?

A

Sympatric speciation - become reproductively isolated when there is no physical separation.

Allopatric speciation - Become reproductively isolated because physically separated

78
Q

Explain how a new species is formed when a population becomes geographically isolated?

A

1) Populations of the same species are geographically separated
2) They will experience slightly different conditions for example there might be a different climate on the other side of the physical barrier
3) Populations will experience different selection pressures (due to different conditions) and so different changes in allele frequencies will occur.
4) Changes in allele frequencies lead to differences in the gene pools of the separated populations which lead to a change in phenotype frequencies.
5) Eventually individuals from the populations have changed so much that they can no longer bridge to produce fertile offspring – they are reproductively isolated.
6) The two groups have become separate species

79
Q

Explain how a new species is formed when a population becomes geographically isolated?

SUMMARY (6)

A

1) isolation
2) different conditions
3) change in alleles frequency
4) leads to change in gene pool and phenotype frequency
5) can’t interbreed to produce fertile offspring
6) separate species

80
Q

If a population has become geographically isolated, name three ways the allele frequency may change

A

1) Different alleles will be more advantage in the different populations because they are in different environments
2) Are you frequencies will change as mutations occur independently in each population
3) Genetic drift may also affect our little frequencies in each of the separate populations

(Different alleles arise because of different environments, random mutations in separate populations, random genetic drift in separate populations)

81
Q

What does sympatric speciation not require?

A

Geographical isolation

82
Q

When does sympatric speciation occur?

A

When populations of a species that share the same habitat become reproductively isolated from each other

83
Q

XXX so if sympatric speciation occurs with polyploidy

Allopatric speciation occurs when geographically isolated

Can speciation occur when u just have MVARPS occurring in a population that are all in one place or does this just cause diversity amongst the species but no actual new species because no reproductive isolation ??

A

ASK O’DONNELL

84
Q

Give an example of sympatric speciation

A

X

85
Q

Diploid

A

Two sets of chromosomes (one from each parent)

Chromosome 12, two chromosome 12s because one from each parent

86
Q

Haploid

A

Cell has a single set of chromosomes

87
Q

Polyploidy

A

Condition where cells have more than two homologous paired sets of chromosomes

(So chromosomes come in pairs but polyploidy would be if you had like a set coming in threes but you had like 6 sets which are meant to be pairs but are instead threes)

Eg. Three chromosome 12s

88
Q

Aneuploidy

XXX

A

???

89
Q

Give an example of sympatric speciation

A

Polyploidy organism emerging in a diploid population.

Polyploid organism is reproductively isolated from diploid organisms.

If polyploid organisms reproduces asexually, a new species may develop

BUT Polyploidy can only lead to speciation if it doesn’t prove fatal to the organism and more polyploid organisms can be produced.

90
Q

In which species is it more common for polyploidy to lead to speciation and why?

A

Plants than animals

Plants can self fertilise and reproduce asexually
Whereas
Animals that are polyploidy would need to find another animal of the same species but opposite sex who is also polyploidy

91
Q

Reproduction isolation occurs because…

A

Changes in alleles and phenotypes and some individuals prevent them from breeding successfully with individuals that haven’t had these changes

92
Q

What types of changes might occur that could lead to reproductive isolation (individuals of same species being unable to breed)? (3)

A

1) Seasonal changes – individuals from same population develop different flowering on meeting seasons or become sexually active at different times of the years
2) Mechanical changes – changes in genitalia prevent successful meeting
3) Behavioural changes – a group of individuals develop courtship rituals that are NOT attractive to the main bulk of individuals in the population so they no longer mate

93
Q

Explain how genetic drift leads to speciation

XX does genetic drift only occur in isolated populations or can it occur in normal population and then lead to speciation ???

A

Individuals within a population show variation in the genotypes

An allele is passed on by chance to offspring more often to usual

By chance the number of individuals with this allele increases.

XXX Changes an allele frequency into isolated populations could eventually lead to reproductive isolation and speciation XXXX

94
Q

When does evolution by genetic drift have a greater effect?

A

In smaller populations where chance has a greater influence.

95
Q

When does evolution by genetic drift have a smaller effect?

A

In larger populations, any chanced variations in allele frequency tends to even out across the whole population

96
Q

What drives evolution?

A

Natural selection and genetic drift

97
Q

What 5 things can cause speciation?

A 
Genetic drift
Geographical isolation
Polyploidy 
Natural selection
Anything that causes reproductive isolation
98
Q

What is the diversity of life on Earth today as a result of?

A

Speciation and evolutionary change over millions of years.

To start with there was one population of organisms which then evolved into more species which evolved into more species and this process was repeated again and again

AQA A level Biology (36 decks)

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