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A-Level Biology - AQA > ✅18 - Populations And Evolution > Flashcards

✅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 can interbreed.

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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 allelic frequency?

A

The number of times an allele occurs within the gene pool

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4
Q

How does the number of organisms compare to the number of alleles in a gene pool?

A

The number of alleles is twice the number of organisms as every organism has two copies in each of their cells

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5
Q

What is the Hardy-Weinberg principle?

A

Provides 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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6
Q

What assumptions does the Hardy-Weinberg principle make?

A

No mutations arise
The population is isolated, so no flow of alleles in and out
No selection, so all alleles equally as likely to be passed on
Population is large
Mating within population is random

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7
Q

What is the equation for Hardy-Weinberg?

A

p2 + 2pq + q2 = 1.0

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8
Q

What are the factors which can cause variation?

A

Mutation
Meiosis
Random fertilisation of gametes

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9
Q

How can mutation cause variation?

A

The sudden changes to genes and chromosomes may or may not be passed on to the next generation. Mutations are the main source of variation

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10
Q

How can meiosis cause variation?

A

Produces new combinations of alleles before they are passed into gametes, so all are different

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11
Q

How can random fertilisation of gametes cause variation?

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 random.

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12
Q

How can environmental factors affect an organism?

A

Factors such as height can be influenced by environmental factors, and they influence where on the normal distribution curve the organism lies.

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13
Q

What are selection pressures?

A

The environmental factors that limit the population of a species

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14
Q

What factors does natural selection require to happen?

A

Organisms produce more offspring than can be supported by the available supply of food, light, space etc
There is genetic variety within the populations of all species
A variety of phenotypes that selection operates against

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15
Q

Why do many species produce more offspring than they can support?

A

To ensure a sufficiently large population survives to breed and produce the next generation.

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16
Q

What do high reproduction rates compensate for?

A

High death rates, predation, competition, natural disaster, extremes of temperature etc

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17
Q

What is intraspecific competition?

A

Competition between organisms of the same species

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18
Q

What does the selection process depend on?

A

Individuals being genetically different

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19
Q

Why is having a wide range of genetically different organisms beneficial to a population?

A

Because it means that there will likely be an individual who can survive in almost any new set of circumstances

20
Q

What is stabilising selection?

A

Preserves the average phenotype around the mean of a population by favouring average individuals. Selects against extreme phenotypes

21
Q

What is directional selection?

A

Changes the phenotypes of a population by favouring phenotypes that very in one direction from the mean of the population. Selection for one extreme phenotype

22
Q

What is disruptive selection?

A

Favours individuals with extreme phenotypes rather then those with phenotypes around the mean

23
Q

What is an example of stabilising selection?

A

Fur length in mammals where temperature is constant

24
Q

What is an example of directional selection?

A

Antibiotic resistance in bacteria

25
Q

What is an example of disruptive selection?

A

Coho salmon - small males can sneak up on females in spawning grounds and large males are fierce competitors, intermediate sized ones die out

26
Q

What is an example of evolutionary changes in recent years?

A

The peppered moth

27
Q

What type of selection has the peppered moth undergone?

A

Directional

28
Q

What is evolution by natural selection?

A

A change in the allelic frequencies within a population

29
Q

What is speciation?

A

The evolution of new species from existing ones

30
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

31
Q

How are new species formed?

A

Through reproductive separation followed by genetic change due to natural selection

32
Q

What is adaptive radiation?

A

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

33
Q

What is genetic drift?

A

Takes place in small populations, less genetic diversity, alleles passed on quickly affects whole population and frequency becomes high

34
Q

What is allopatric speciation?

A

Two populations become geographically separated, and if environmental conditions vary then natural selection influences two populations differently

35
Q

What is sympatric speciation?

A

Formation of a new species that results within a population in the same area leading to them becoming reproductively separated

36
Q

What is an example of allopatric speciation?

A

The Galapagos finch - populations spread over different islands and each evolved according to environment

37
Q

What is an example of sympatric speciation?

A

Apple maggot fly - originally laid eggs in hawthorns, but apples introduced later. Females lay eggs on type of fruit which they developed in, same for males they mate with, so flies raised in apples lay eggs on apples, and vice versa for hawthorns

38
Q

What are the isolating mechanisms?

A 
Geographical 
Ecological
Temporal
Behavioural
Mechanical
Gametic
Hybrid sterility
39
Q

What is geographical isolation?

A

Populations isolated by physical barriers eg oceans, mountains rivers

40
Q

What is ecological isolation?

A

Populations inhabit different habitats within same areas, so individuals rarely meet

41
Q

What is temporal isolation?

A

Breeding seasons of each population do not coincide and they do not interbreed

42
Q

What is behavioural isolation?

A

Mating preceded by courtship, which is stimulated by colour or markings of opposite sex, or actions of mate. Any mutations which cause variation in these prevent mating

43
Q

What is mechanical isolation?

A

Anatomical differences may prevent mating occurring

44
Q

What is gametic isolation?

A

Gametes may be prevented from meeting due to genetic or biochemical incompatibility, eg sperm destroyed by chemicals in female

45
Q

What is hybrid sterility isolation?

A

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

A-Level Biology - AQA (22 decks)

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