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A level Biology > Section 7 - 18 Populations and evolution > Flashcards

Section 7 - 18 Populations and evolution Flashcards

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1
Q

What is a population?

A

A group of organisms of the same species that occupies a particular space at a particular time and that canpotentially interbreed

Any species exists as one or more populations.

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2
Q

What is a 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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3
Q

What is the allelic frequency?

A

The number of times an allele occurs within the gene pool.

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4
Q

What does cystic fibrosis effect?

A

Mucus produced by affected individuals is thicker than normal.

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5
Q

How can we work out the allele frequency of mixed populations?

A

The Hardy-Weinberg principle

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6
Q

What does the Hardy-Weinberg principle provide?

A

A mathematical equation that can be used to calculate the frequencies of the alleles of a particular gene in a population.

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7
Q

What assumption is made in the Hardy-Weinberg principle?

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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8
Q

What 5 conditions must be met in order to assume that the proportion of dominant and recessive alleles of any gene in a population remains the same from one generation to the next?

A
  1. No mutations arise
  2. the population is isolated - no flow of alleles into or out of the population
  3. no selection - all alleles are equally likely to be passed to the next generation
  4. population is large
  5. mating within the population is random
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9
Q

EQUATION

Hardy-Weinberg principle.

A

The probability of allele A = p

and the probability of allele a = q

p + q = 1.0

There are only 4 possibilities for two alleles -

AA + Aa + aA + aa = 1.0

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

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10
Q

Why must p + q = 1.0?

A

There are only two alleles and so the probability of one plus the other must be 1.0 (100%)

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11
Q

What factors affect variation in species phenotypes?

A

genetic and environmental factors.

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12
Q

What is the cause of three genetic variations?

A
  • Mainly mutations
  • meiosis
  • random fertilisation of gametes during sexual reproduction
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13
Q

How does genetic variation arise from mutations?

A

Sudden changes to genes and chromosomes may or may not be passed on to the next generation.

Main source of variation.

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14
Q

How does genetic variation arise from meiosis?

A

A special form of nuclear division produces new combinations of alleles before they are passed into the gametes, all of which are therefore different.

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15
Q

How does genetic variation arise from random fertilisation of gametes?

A

In sexual reproduction, this produces new combinations of alleles and the offspring are therefore different from parents.

Which gamete fuses with which at fertilisation is a random process further adding to the variety of offspring two parents can produce.

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16
Q

Give environmental influences that affect the phenotype

A
  • Climatic conditions
  • soil conditions
  • pH
  • food availability
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17
Q

What are the three forms of selection?

A

Stabilising

Directional

Disruptive

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18
Q

How does stabilising selection affect the characteristics of a population?

A

Preserves the average phenotype of a population by favouring average individuals in other words, selection against the extreme phenotypes.

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19
Q

How does directional selection affect the characteristics of a population?

A

CHanges the phenotypes of a population by favouring phenotypes that vary in one direction from the mean of the population, in other words, selection for one extreme phenotype.

20
Q

How does disruptive selection affect the characteristics of a population?

A

Favours individuals with extreme phenotypes rather than those with phenotypes around the mean of the population.

21
Q

What is eliminated due to stabilising selection?

A

Eliminate the extremes of the phenotypes

and with it the capacity for evolutionary change.

22
Q

When is it most likely for stabilising selection to occur?

A

Where the environmental conditions are constant over long periods of time.

23
Q

What graph can be formed due to directional selection?

A

normal distribution curve.

A mean that represents the optimum value for the phenotypic character under the existing conditions.

24
Q

What is the result of the directional selection?

A

one extreme of a range or variation being selected against in favour of the other extreme or even the average.

25
Q

What is the opposite of stabilising selection?

A

Disruptive selection

26
Q

What does disruptive selection favour?

A

extreme phenotypes at the expense of the intermediate phenotypes.

27
Q

When does disruptive selection occur?

A

When an environmental factor, such as temperature, takes two or more distinct forms.

28
Q

What is polymorphism?

A

Some species of organisms have two or more distinct forms.

These different forms are genetically distinct but exist within the same interbreeding population.

29
Q

What is the allelic frequency?

A

The number of times an allele occurs within the gene pool.

Affected by selection which is due to environmental factors.

30
Q

What is speciation?

A

The evolution of new species from existing ones.

31
Q

What is a species?

A

A group of individuals that have a common ancestry and so share the same genes but different alleles and are capable of breeding with one another to produce fertile offspring.

Members of a species are reproductively separated from other species.

32
Q

What is adaptive radiation?

A

The different phenotypes each combination of alleles produces will be subject to selection pressure that will lead to each population becoming adapted to its local environment.

33
Q

What is the result of adaptive radiation?

A

CHanges to the allele frequencies of each population and so each population evolves.

Populations will no longer be able to interbreed successfully.

As each population would be a different species each with its own gene pool.

34
Q

When can genetic drift happen?

A

In small populations

35
Q

Why does genetic drift happen in small populations?

A

The relatively few members of small populations possess a smaller variety of alleles than the members of a large population.

Their genetic diversity is less.

36
Q

What are the two forms of speciation?

A

allopatric speciation

sympatric speciation

37
Q

What does allopatric mean?

A

Different countries.

38
Q

What is allopatric speciation?

A

Where two populations become geograohically separated.

This can be the result of any physical barrier between two populations which prevents them interbreeding.

39
Q

What does sympatric mean?

A

Same country

describing the form of speciation that results within a population in the same area leading to them becoming reproductively separated

40
Q

State the 7 types of variation

A
  1. Geological
  2. Ecological
  3. Temporal
  4. Behavioural
  5. Mechanical
  6. Gametic
  7. Hybrid sterility
41
Q

What is the geological variation?

A

Populations isolated by physical barriers such as oceans, mountain ranges, rivers

42
Q

What is ecological variation?

A

Populations inhabit different habitats within the same areas and so individuals rarely meet.

43
Q

What is temporal variation?

A

The breeding seasons of each populations do not coincide and so they do not interbreed.

44
Q

What is behavioural variation?

A

Any mutations which cause variations in courtship patterns may prevent mating.

45
Q

What is mechanical variation?

A

Anatomical differences may prevent mating occuring.

46
Q

What is gametic variation?

A

Prevented from meeting due to genetic or biochemical incompatibility.

47
Q

What is hybrid sterility variation?

A

Hybrids formed from the fusion of gametes from different species are often sterile because they cannot produce viable gametes.

A level Biology (12 decks)

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