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A Level Biology Paper 2 > Section 7 - Chapter 18: Populations and Evolution - old > Flashcards

Section 7 - Chapter 18: Populations and Evolution - old Flashcards

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1
Q

What is discontinuous data and name examples

A
  • Data falls into distinct categories (no intermediate types)
    • Gender, Blood Group
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2
Q

What is continuous data and name examples

A
  • Data can have intermediate values - no distinct categories
  • Arm span, skin tone, height
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3
Q

What are the 2 different types of factors that show variation in phenotype

A
  • Genetic and environmental factors
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4
Q

Genetic variation arises as a result of…

A
  • Mutations - changes in DNA base sequence
  • Meiosis - creates new combinations of alleles
  • Random Fertilisation of gametes
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5
Q

Where variation is due to genetic factors organisms fit into …. known as …..

A

Where variation is due to genetic factors organisms fit into a few distinct categories known as discontinous data

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6
Q

What is genetic variation controlled by and how can this be graphically represented

A
  • Controlled by a single gene
  • Bar chart or pie chart
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7
Q

Name sone environmental factors that can influence how genes are expressed

A
  • Climatic conditions, temperature, rainfall, soli conditions, food availability
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8
Q

What is a continuum and how is environmental factors controlled by

A
  • Some characteristics grade into 1 another
  • Not controlled by a single gene but by many genes (polygenes)
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9
Q

How can environmental variation be graphically presented

A

Line-graph, bell-shaped curve, normal distribution curve

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10
Q

What are the environmental factors that limit the population of species called and name examples

A
  • Selection Pressures - these determine the frequency of alleles within a gene pool
  • Predation, competition and disease
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11
Q

What is a gene pool

A
  • Is the total number of all the alleles of all the genes of all the individuals within a particular population at a given time
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12
Q

What are the factors that the process of evolution by natural selection depends on

A
  • Organisms produce more offspring than can be supported by the available supply of food, light, space
  • There is genetic variety within the populations of all species
  • A variety of phenotypes that selection operates against
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13
Q

What is the link between natural selection and over production

A
  • When there are too many offspring for the available resources, there is competition amongst individuals
  • The greater the numbers, greater the competition - more death
  • Individuals best suited survive and breed and pass on favourable alleles to offspring
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14
Q

What is the role of variation in natural selection

A
  • Conditions change over time and having a wide range of different alleles means some will have combinations needed to survive.
  • These survive and pass on favouable alleles - change allele frequency
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15
Q

What happens to populations that show little genetic variation

A
  • More vulnerable new diseases and climate change
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16
Q

What are the 3 main types of selection that affect characteristics of a population

A
  • Stabilising Selection
  • Directional Selection
  • Disruptive Selection
17
Q

What is Selection

A
  • A process by which only the organisms better adapted to their environment, survive, breed and pass on favourable alleles
18
Q

What is Stabilising Selection and name an example

A
  • Eliminates the extremes of the phenotype. It favours the mean
  • It tends to occur when environmental conditions are constant over a period time
  • Reduces range of phenotype
  • Human birth weight
19
Q

What is Directional Selection and name an example

A
  • 1 extreme phenotype more likely to survive
  • Environment changes characteristics of the population changes over time
  • Peppered moths
20
Q

What is Disruptive Selection

A
  • 2 different extremes are favoured
  • When an environmental factor such as temperature takes 2 or more distinct forms
21
Q

What is allelic frequency

A
  • The number of times an allele occurs in a gene pool this affected by selection
22
Q

What is speciation

A
  • Is the evolution of new species from existing ones
  • Members of a species are reproductively separated from other species
  • It is through speciation that evolutionary change has happened over millions of years
23
Q

How are new species formed

A
  • Through reproductive separation followed by genetic change due to natural selection
24
Q

What is adaptive radiation

A

Different phenotypes each combination of alleles produces due to selection pressures that will lead to the population being adapted and results in changes in the allele frequencies

25
Q

How a new species is formed summary

A
  1. Population becomes separated (could be due to geographical isolation which causes reproductive isolation/separation)
  2. Within a population genetic variation exists (due to mutations)
  3. No interbreeding
  4. Each new environment exerts different selection pressures and species become adapted to their own environment (adaptive radiation)
  5. Best adapted are selected - natural selection
  6. Causes change in allele frequency
  7. If 2 populations come back they can’t interbreed - speciation. Gene pools are different
26
Q

What is genetic drift

A
  • Takes place in small populations - possess small variety of alleles
  • This is when chance rather than the environment dictates which organisms survive and breed
27
Q

What are the 2 forms of speciation

A
  • Allopatric
  • Sympatric
28
Q

What is Allopatric Speciation

A
  • Where 2 populations become geographically separated
  • These barriers include oceans, rivers, mountains
  • Physical barriers prevent interbreeding (reproductively isolated)
  • Environmental conditions can vary either side, then natural selection will influence 2 populations differently and each will evolve leading to changes in allelic frequencies
29
Q

What is sympatric speciation

A
  • Speciation that results within a population in the same area leading them to be reproductively isolated
  • Not Geographically isolated
30
Q

Why populations maybe reproductively isolated if there is no Barrier

A
  • Mutations
  • They develop differences in their gene pools e.g. changes in courtship behaviours, seasonal differences
    • Therefore, different alleles selected for and passed on - changes allele frequency
    • Example of disruptive natural selection
31
Q

Name some reproductive isolation mechanisms

A
  • Behavioural - produce different songs/ colourings - don’t attract mates
  • Mechanical - change in genitalia - physically not possible
  • Temporal - Different flowering times
32
Q

How can speciation occur in plants

A
  • A random mutation that causes plants to become polyploidy (extra set of chromosomes)
  • Those with polyploidy can’t breed to produce fertile offspring - therefore reproductively isolated
  • If species reproduces asexually and survives the mutation, a new species can develop.
    *
33
Q

Exam Question: The 2 species diverged from each other after the island was formed 6.5 million years ago. The flowering times of the 2 species are different. Suggest how the 2 species arose by sympatric speciation

A
  1. Occurs in the same environment
  2. Mutations cause different flowering times
  3. Reproductive separation/isolation
  4. Different alleles passed on/ change in frequency of alleles
  5. Disruptive natural selection
  6. Eventually different species can’t interbreed to produce fertile offspring
    7.
34
Q

What are the factors that affect allele frequencies

A
  • Natural Selection
  • Mutations
  • Genetic Drift - when chance rather than the environment dictates which survive - impacts smaller populations
35
Q

What is the founders effect

A
  • The loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population
36
Q

What is Genetic Bottlenecks

A
  • A sharp reduction in population sizes due to environmental events and human activities
  • Population bottlenecks produce a smaller population with reduced genetic diversity
  • In subsequent generations, genetic diversity remains lower only increase by mutations.

A Level Biology Paper 2 (10 decks)

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