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A-Level Biology A2 > Population And Evolution > Flashcards

Population And Evolution Flashcards

1
Q

What is the definition of species?

A

A group of similar organisms that can reproduce to give fertile offspring.

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2
Q

What is the definition of population?

A

A group of organisms of the same species living in a particular area at a particular time that can interbreed.

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3
Q

What is the definition of gene pool?

A

Completed range of alleles present in a population.

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4
Q

What is the definition of allele frequency?

A

How often an allele occurs in a population.

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5
Q

What does the hardy-weinberg principle predict?

A

Predicts that the allele frequencies will not change from one generation to the next generation. But only under certain conditions i.e. no immigration, no emigration, no mutation, no natural selection.

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6
Q

What are the conditions that the hardy-weinberg principle needs to support the prediction?

A
  • has to be a large population.
  • no immigration
  • no emigration
  • no mutations
  • no natural selection
  • random mating - all possible genotypes can breed with all others.
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7
Q

What is the hardy weinberg equation used for?

A

predicting frequency of alleles, genotypes and phenotypes and test whether HWP applies to a particular allele in a particular population.

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8
Q

What is the hardy weinberg equation for allele frequency?

A

p + q = 1

p = dominant allele

q = recessive allele

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9
Q

What is the hardy weinberg equation for phenotype frequency?

A

p2 + 2pq + q2 = 1

p2 = freq. of homozygous dominant genotype

q2 = freq. of homozygous recessive genotype

2pq = freq. of heterozygous genotype

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10
Q

How would you work out the percentage of a population that has a certain genotype?

A
  1. find the freq. of heterozygous genotype.
  2. calculate q.
  3. caculate p.
  4. calculate 2pq.
  5. x 100.
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11
Q

Show if external factors are affecting allele frequency.

i.e. if freq. of CY is measured 50 years later and the first value for q was 0.02, has the value changed if its measured 1/3500.

A

q2 = 1/3500 = 0.00029

q = square root of 0.00029 = 0.017

so the principle doesn’t apply meaning there must of been other factors affecting the allele frequency i.e. immigration, emigration, mutations or natural selection.

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12
Q

What drives evolution?

A

Natural selection

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13
Q

What changes a population?

A

Genetic drift

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14
Q

What is speciation?

A

The development of a new species from an existing species.

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15
Q

When does speciation occur?

A

When populations of the same species become reproductively isolated.

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16
Q

What can cause changes in the phenotype

A

changes in the alleles frequency due to a physical barrier

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17
Q

A change in the phenotype leads to what?

A

Species no longer being able to interbreed to produce fertile offspring.

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18
Q

What is geographical isolation?

A

A physical barrier formed from a flood or an earthquake divides a population of a species, causing some individuals to become separated from the main population.

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19
Q

What can geographical isolation lead to?

A

Allopatric speciation

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20
Q

What is sympatric speciation?

A

Organisms in the same population. When speciation can occur in a population by it becoming reproductively isolated without any physical separation (not due to geographical isolation).

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21
Q

What does allopatric speciation require?

A

Geographical isolation

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22
Q

What will populations that are G.I experience?

A

diff. conditions i.e. diff climates on either side of physical barrier.
diff. selection pressures

different changes in allele frequencies.

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23
Q

Explain the process of species becoming separate/ geographical isolation

A
  1. different alleles will be more advantageous in the different populations. - more advantageous allelei.e in the cold they’d benefit from longer fur length so directional selection will act on the alleles for fur length in the population, increasing the freq. of allele for longer fur.
  2. allele freq. will change as mutations occur independently in each population.
  3. genetic drift may also affect the allele freq. in one or both populations.
  4. the changes lead to differences in the gene pools of the separated populations causing changes in phenotypes freq.
  5. The individuals would of then changed so much that they won’t be able to breed with one another to produce fertile offspring - become reproductively isolated.
  6. The two groups would of then became separate species.
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24
Q

Explain how speciation of the cichlids may have occurred following the formation of separate, smaller lakes.

A
  1. Geographical isolation.
  2. One side could of had different environmental conditions causing the species in that area having to adapt and survive.
  3. Causes change in the alleles and behaviour so the frequency of alleles change.
  4. Unable to reproduce to produce fertile offspring due to the gene pools now being separate.
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25
Q

Explain how very high diversity of bird species has developed in the Amazonian forest

A
  1. Geographical isolation.
  2. Causes genetic variation/ mutation.
  3. Two separated areas form a different habitat as different environmental conditions/ different selection pressures.
  4. Adapted organisms survive and breed/ differential reproductive success.
  5. allele frequency is increased/ changed.
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26
Q

Speciation is far less frequent in the reformed amazonian forest. Suggest one reason for this.

A

Similar/ same environment/ abiotic/ biotic factors

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27
Q

What doesn’t sympatric speciation not require?

A

Geographical isolation.

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28
Q

What is polyploidy?

A

Mutations can occur that increase the number of chromosomes. It is reproductively isolated from the diploid organisms and can reproduce asexually since it can’t sexually, which can develop a new species.

29
Q

Why does reproductive isolation occur?

A

due to changes in the alleles and phenotypes in some individuals prevents them from breeding successfully with individuals without these changes.

30
Q

What are the changes in reproductive isolation (preventing individuals from breeding)?

A
  1. seasonal - individuals from the same population develop diff. flowering or mating seasons, or become sexually active at diff. times of the year.
  2. mechanical - changes in genitalia prevent successful mating.
  3. behavioural - a group of individuals develop courtship rituals that aren’t attractive to the main population.
31
Q

What can genetic drift lead to?

A

Speciation

32
Q

What can change the allele frequency?

A

Different selection pressures.

33
Q

What is evolution by natural selection?

A

Different selection pressures change the allele freq. in two geographically isolated species.

34
Q

Other than geographical isolation, how else might evolution occur?

A

Due to genetic drift.

35
Q

What is genetic drift?

A

When chance dictates which alleles are passed on, not environmental factors. (individuals survive, breed and pass on their alleles).

36
Q

Describe the process of genetic drift

A
  1. individuals within a population show variation in their genotypes.
  2. by chance, the allele for one genotype is passed on to the offspring more often than others.
  3. so the number of individuals with the allele increases.
  4. changes in the allele freq. in two isolated populations could eventually lead to reproductve isolation and speciation.
37
Q

when does evolution by genetic drift usually have a greater effect?

A

In smaller populations where chance has a greater influence.

38
Q

Whattends to happen to the allele freq in larger population?

A

Any chance variations in allele freq. tends to even out across the whole population.

39
Q

Why might individuals within a population of a species show a wide range of variation in phenotype?

A

due to genetic and environmental factors.

40
Q

Those organisms with phenotypes providing selective advantages are likely to…

A

produce more offspring and pass on their favourable alleles to the next generation.

41
Q

Explain how different subspecies of giraffe may have evolved from a common ancestor

A
  • no interbreeding
  • mutation linked to colour
  • selection linked to colour
  • adapted organisms breed
  • change in allele freq - increases
  • most advantageous allele most likely to survive, reproduce and produce fertile offspring
42
Q

Biologists compared DNA of diff subspecies. They used results from comparing this DNA to conclude that 6/9 subspecies are separate species. Suggest how they came up with this conclusion

A
  • compare base sequences
  • each different in each species
43
Q

Describe one way in which scientists could find out whether cichilds from two diferent populations belng to the same species.

A
  • if they are the same species, they will reproduce
  • to produce fertile offspring
44
Q

What has evolutionary change resulted in?

A

Great diveristy of organsims

45
Q

The diversity of life on earth today is the result of what?

A

speciation and evoluntionary change over millions of years.

46
Q

Explain evolutionary change

A
  • to start off with there was one population of organisms.
  • that population was divided and the new population evolved into separate species.
  • the new species were then divided again and the new populations evolved into more separate species.
  • that process has been repeated over a long period of time to create millions of new species.
47
Q

What can variation be caused by?

A

genes and the environment

48
Q

What does variation within a species mean?

A

That individuals in a population can show a wide range of different phenotypes.

49
Q

What causes genetic variation within a species?

A

Although individuals of the same species have the same genes, they have different alleles (versions of genes).

50
Q

What causes genetic variation?

A

Different alleles.

51
Q

What is the main source of genetic variation?

A

Mutation

52
Q

What other way other than mutation is genetic variation caused?

A

by crossing over of chromatids during meiosis

by independant segregation

by random fertilisation

53
Q

How is most variation within a species caused?

A

by combination of genetic and environmental factors

54
Q

What results in evolution?

A

Genetic variation

55
Q

What is evolution?

A

A change in allele frequencies in a population over time

56
Q

Natural selection causes what to occur?

A

evolution

57
Q

In terms of alleles what is evolution?

A

when the freq. of alleles in a population changes over time.

58
Q

Explain natural selection

A
  1. Individuals of the same species vary because they have different alleles.
  2. Predation, disease and competition (selection pressures), creates a struggle for survival.
  3. Because individuals vary, some are better adapted to the selection pressures than others.
  4. That means there are differential levels of survival and reproductive success in a population. Individuals with a phenotype that increases chance of survival are more likely to survive, reproduce and pass on their genes and advantageous alleles than individuals with diff phenotypes.
  5. This means that a greater proportion of the next generation inherit the beneficial alleles.
  6. So more likely to survive, reproduce and pass on genes.
  7. The freq. of beneficial alleles in the gene pool increases from generation to generation.
59
Q

What are pressures that affect chance of survival are?

A
  • predation
  • disease
  • competition
60
Q

What are the different types of natural selection?

A
  • Stabilising
  • Directional
  • Disruptive
61
Q

What is stabilising selection?

A
  • Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce. It occurs when the environment isn’t changing, and it reduces the range of possible phenotypes.
  • Eliminates the extremes.
62
Q

Give an example of stabilising selection

A
  • In any mammal population there’s a range of fur length. In a stable climate, having fur at the extremes of this range reduces chances of surviving as its harder to maintain the right body temperature.
  • Animals with alleles for average fur length are most likely to survive, reproduce and pass on their alleles.
  • So these alleles increase the frequency.
  • The proportion of the population with the average fur length increases and the range of fur lenghts decreases.
63
Q

What is directional selection?

A
  • Where individuals with alleles for a single exteme phenotype are more likely to survive and reproduce. This could be a response to an environmental changing so optimum value for survival changes.
64
Q

Give an example of directional selection

A
  • Cheetahs
  • Individuals with alleles for increased speed = more likely to catch prey and survive, reproduce and pass on alleles
  • Overtime the freq. of alleles increases.
65
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. It’s the opposite of stabilising selection because characterisitics towards the middle of the range are lost.
  • It occurs when the environment favours more than one phenotype.
66
Q

Give an example of disruptive selection

A
  • beak sizes in birds
  • birds with large beaks are specialised to eat large seeds
  • birds with small beaks are specialised to eat small seeds
  • birds with medium sized are less likely to survive as unabel to eat eithr big or small.
  • large and small beaks more likely to survive, reproduce and pass on alleles, so increase in frequency.
  • medium size beak alleles decrease in frequency.
67
Q

Anolis sagrei is a species of lizard that is found on some of the smallest Caribbean islands.

Describe how you could use the mark-release-recapture method to estimate the number of Anolis sagrei on one of these islands.

A
  1. Capture / collect sample, mark and release;
  2. Method of marking does not harm lizard / make it more visible to predators;
  3. Leave sufficient time for lizards to (randomly) distribute (on island) before collecting a second sample;
  4. (Population =) number in first sample × number in second sample divided by number of marked lizards in second sample / number recaptured.
68
Q

Explain how the Caribbean species could have evolved.

A
  1. Geographic(al) isolation;
  2. Separate gene pools / no interbreeding / gene flow (between populations)/ reproductive isolation
  3. Variation due to mutation;
  4. Different selection pressures / different abiotic / biotic conditions / environments / habitats;
  5. Different(ial) reproductive success / selected organisms (survive and) reproduce/ pass on alleles / genes to next generation as equivalent to reproduce
  6. Leads to change / increase in allele frequency/ increase in proportion / percentage as equivalent to frequency
69
Q
A

A-Level Biology A2 (11 decks)

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