Download Evolution

Starter
Outline how variation, adaptation and selection are
major components of evolution [4]
 Variation must exist before evolution can occur
 Environment can select those variations that give an
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advantage
Selection pressure
Those with advantage survive and reproduce
Next generation has that advantageous characteristic
Over time species becomes better adapted to its
environment
Natural selection
Learning Objectives
 To understand modern day examples of evolution
Success criteria
 Outline how variation, adaptation and selection are
major components of evolution
 Discuss why the evolution of pesticide resistance in
insects and of drug resistance in microorganisms has
implications for humans
Evolution in action
 Drug resistance in microorganisms
 Pesticide resistance in insects
Video
Antibiotic resistance
Staphylococcus aureus is a bacterium that can
be found on the skin and in the throat.
It causes a range of illnesses from minor skin infections
to life-threatening diseases such as meningitis and
septicaemia.
Antibiotic resistance and MRSA
Some strains of Staphylococcus aureus have evolved become
resistant to one or more of the commonly used antibiotics
including methicillin.
 These are termed methicillin-resistant Staphylococcus
aureus (MRSA).
 Methicillin Susceptible Staphylococcus aureus (MSSA).
This form is still contained by the use of the antibiotic
Methicillin.
 MRSA is especially prevalent in hospitals:
 Here patients tend to be more vulnerable to the infection i.e.
older, sicker and weaker.
 People live together and are examined by doctors and nurses
that have just touched other patients.
 Many antibiotic strains are used, any resistant strains
therefore have an advantage.
This image shows the increase in the increased
frequency of MRSA from samples in USA hospitals
The genome for S. aureus was completed at the Sanger
Institute and published in June 2004.
Comparison of the genomes for the two forms shows
significant differences between MRSA and MSSA.
Antibiotic resistance
Evolution by natural selection:
 Applying an antibiotic to a population of bacteria
applies a very strong selection pressure in favour of
mutants able to resist the antibiotic.
 This resistance is then inherited by offspring or it can
be passed on via plasmids between bacteria. The
resistance gene increases in frequency in the
population
 The species has evolved into two new forms – resistant
(MRSA)and non-resistant (MSSA).
Antibiotic use
 Antibiotics are used very widely, sometimes unnecessarily
through patient pressure.
 If used appropriately when a disease has been diagnosed
then the infection may be eradicated. However, the patient
must complete the whole course of antibiotic.
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Sometimes patients stop taking the antibiotic as soon as they feel
well. Doing this aids the development of resistance, as some of the
bacteria may still be alive at this point, and these are going to be the
very ones that are most resistant to the drug’s effects.
 Antibiotics are sometimes used to treat viral diseases,
because they may help prevent secondary bacterial
infections to which the patient may be vulnerable.
Pesticide Resistance
 Your turn now, using texbook review pesticide
resistance in insects
Plenary Questions
Explain why evolution occurs in a shorter time in populations
of microorganisms than in populations of mammals
1.
Microorganisms have short life cycle
• Every generation can have mutations arise
• Selection pressure can change species in just a few
generations
In mammals life cycle is longer and mutations less frequent
Explain why evolution tends to happen in short bursts
2.
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When environment changes this applies new selective pressures.
If variations are advantageous these are selected, species
changes.
Once species is well adapted to new environment changes slow
or stop.