5.4: Evolution Evolution is the cumulative change in the
heritable characteristics of a population.
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SPECIES AND POPULATIONS EVOLVE INDIVIDUALS DO NOT EVOLVE
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5.4.2: Fossil record A fossil is any physical evidence about a
dead organism. Some fossils are only fragments of bone, teeth or
shells. Amber fossils sometimes contain intact bodies of insects
and small amphibians. Rock fossils show complete details of
external structures.
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5.4.2: Homologous structures Structures derived from the same
body part of a common ancestor are called homologous structures.
One example of a homologous structure is the pentadactyl limb,
which is an appendage comprised of five bones.
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5.4.2: Selective breeding Selective breeding is the process
used by breeders to develop a plant or animal over time with
desired characteristics.
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5.4.3: Overpopulation STATE: Populations tend to produce more
offspring than the environment can support
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5.4.4: Struggle for survival Populations tend to produce more
offspring than the environment can support; and this
over-production of offspring results in a struggle for survival.
The fittest individuals are those with the best genes; in other
words, those with the most favorable heritable variations. The
fittest individuals are the most likely to survive long enough to
reproduce and pass on their genes; and the weakest individuals are
more likely to die young and not pass on their genes.
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N09/4/BIOLO/SP2/ENG/TZ0/XXExplain how sexual reproduction can
lead to variation in a species. [3] allows characteristics from
both parents to appear in offspring; crossing over (during prophase
1) changes chromosome composition; produces gametes which are all
different; random chance of which sperm fertilizes ovum; greater
variation (resulting from sexual reproduction) favours survival of
species through natural selection; [3 max] Accept independent
assortment during meiosis from AHL.
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M08/4/BIOLO/SP2/ENG/TZ1/XX+ (b) Outline how sexual reproduction
can give rise to genetic variation in a population. meiosis;
crossing over; independent assortment; sexual
reproduction/fertilization/recombination; mutations; environmental;
[2 max]
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5.4.5: Variation within a species STATE: Members of a species
show variation
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5.4.5: Sexual reproduction Variation exists between members of
one species, which means that some individuals are better suited
for survival than others. The sources of variation are: 1)mutation,
which creates new alleles in the first place; 2) meiosis, which
enables each parent to produce millions of different gametes (each
with a unique combination of chromosomes); and 3) sexual
reproduction, fertilisation and mate selection
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Individuals that are better suited to changes in the
environment survive and pass on their genes for surviving
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5.4.7: Natural Selection Deduction 1: Populations produce more
offspring than the environment can support. Deduction 2: The
over-production of offspring results in a struggle for survival and
nature selects the fittest individuals. Deduction 3: The fittest
individuals survive long enough to reproduce and pass on their
genes; the weakest individuals die young and fail to pass on their
genes. Thus natural selection leads to the increased reproduction
of individuals with favorable heritable variations. Charles Darwin
Alfred Wallace
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5.4.8: Evolution in Response to Environmental Change Name of
population: The tuberculosis bacterium Characteristic under
evolution: Resistance to the antibiotic Rifampicin Environmental
change: Exposure to an inadequate dose (or inadequate duration) of
the antibiotic Response 1: When patients receive an inadequate dose
(or inadequate duration) of the antibiotic then some of the
bacterial population may survive. Each bacterium that is killed by
the antibiotic has a particular allele that codes for the
particular protein that the antibiotic targets. And conversely,
each bacterium that survives the antibiotic must be lacking the
particular allele that codes for the particular protein that the
antibiotic targets. Response 2: When a surviving bacterium divides
it passes on its antibiotic- resistant allele to its two daughter
cells. Having inherited the antibiotic-resistant allele, the two
offspring survive, reproduce and increase the antibiotic-resistance
gene in the population. After several generations the population
can become resistant to the antibiotic.
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Natural Selection DDT Resistance in Anopheline Mosquitoes
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The malarial parasite is spread by anopheline mosquitoes The
spread of malaria can be controlled by controlling mosquito numbers
One way of controlling mosquito numbers is to use an insecticide
like DDT DDT
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Not every mosquito will be killed each time we spray Some will
survive to repopulate the area, so we must spray frequently.
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Random mutation may produce mosquitoes which are resistant to
the effects of DDT these are more likely to survive and pass on
their genes to the next generation
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NOTE A resistant mosquito does not need to be totally immune to
the effects of DDT it may just be able to survive higher does of
DDT than normal mosquitoes.
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The next generation contains more resistant mosquitoes Again,
they are more likely to survive to reproduce, so the proportion of
the population which is resistant to DDT increases
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With each successive generation the proportion of the mosquito
population which is resistant to DDT increases.
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Eventually, the whole population may consist of resistant
mosquitoes
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Spraying with DDT produces the selective pressure which favours
the resistant mosquitoes. Because they can resist the effects of
DDT, the resistant mosquitoes are said to have a selective
advantage
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It may not be able to increase the dose of DDT used: - higher
doses may be dangerous to humans - higher doses may be too damaging
to other wildlife Using higher doses of DDT will also produce the
selective pressure which will favour mosquitoes with even higher
levels of resistance
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Explain how natural selection can lead to evolution using
antibiotic resistance in bacteria as an example. [9]
M11/4/BIOLO/SP2/ENG/TZ2/XX members of a population of the same
species show variation; some organisms are more likely to survive
due to selective advantage / survival of the fittest; some
organisms have a reproductive advantage; these variations may be
genetically controlled/heritable; these genes are most likely to be
passed on to offspring; this can change the characteristic of the
population; bacteria can normally be killed with antibiotics;
antibiotics impose a selection pressure; if a few bacteria have
natural resistance to the antibiotic they will survive; if the
resistance is heritable they will pass it on to their offspring;
they will reproduce/evolve to form bacterial colonies resistant to
the antibiotic; example of organism selected by use of antibiotic;
(e.g. MRSA bacteria / resistant TB bacteria) [9 max]
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M08/4/BIOLO/SP2/ENG/TZ1/XX+ (c) Explain two examples of the
evolution of specific populations of organisms in response to
environmental change.[5] [5] [8] Two examples required. Award [4
max] for each example. Example 1 name of population and
characteristic: e.g. antibiotic resistance in bacteria (for example
Gonorrhea); environmental change: exposure to the antibiotic;
response 1: antibiotic-sensitive bacteria die /
antibiotic-resistant ones survive; response 2: pass on
antibiotic-resistance gene/inherited trait; drug-resistance gene
transferred to other bacteria (by plasmids); over time resistance
in the population is increased; Example 2 name of population and
characteristics: Galapagos finches, some with strong/big beaks and
some with small beaks; environmental change: wet years with
abundant small seed change to drought years with only large seeds
(as a prevalent food source); response 1: small beaked finches die
leaving primarily finches with strong/large beaks / vice versa;
response 2: finches with large beaks survive to pass gene/inherited
trait to offspring; over time large beaks predominate; [8 max]
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M06/4/BIOLO/SP2/ENG/TZ1/XX Explain briefly how natural
selection could lead to evolution. [3] species produce more
offspring that can survive; populations will show variation;
individuals with favourable traits will survive; some variations
are inherited; favourable (inherited) variations will increase in
numbers; accept converse answer environmental changes will provide
further selection; sustained selection of favourable traits will
result in evolution / results in speciation; [3 max] Evolution or
speciation must be addressed in order to receive full marks. N.B.
Examples are acceptable only if they support marking points given
above.
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M05/4/BIOLO/SP2/ENG/TZ2/XX Discuss the theory of evolution by
natural selection.[8] species produce more offspring that can
survive; populations will show variation; individuals with
favourable traits will survive; some variations are inherited;
favourable (inherited) variations will increase in numbers; accept
converse answer environmental changes will provide further
selection; sustained selection of favourable traits will result in
evolution / results in speciation; Evolution or speciation must be
addressed in order to receive full marks. N.B. Examples are
acceptable only if they support marking points given above.
