10.8 Changing population characteristics

10.8 Changing population characteristics

1. Natural Selection

   • 1. Variation
     • Organisms of a species show variation due to genetics
     • Mutations can occur giving rise to new alleles
   • 2. Selection (survival of the fittest)
     • Organisms with favorable characteristics to a particular selection pressure have an increased chance of survival and therefore reproduction
   • 3. Individuals with an advantage will survive and reproduce hence passing on genes
   • 4. Adaptation
     • Over many generations the frequency of the advantageous allele will increase
     • Hence overtime a group of organisms becomes well adapted to its environment
   • 5. Speciation
     • With the involvement of multiple genes and over many generations its possible for a new species to form

2. Antibiotic resistant bacteria

   • A mutation giving resistance gives the individuals a selective advantage
     • It survives
       • It reproduces
         • Passes on resistant allele to offspring
           • Overtime number of resistant types of bacteria increase
   • Some antibiotics are now ineffective
     • Methicillin resistant staphylococus aureaus (MRSA) is now resistant to an increasing range of antibiotics

3. Pesticide resistance

   • Insecticide applies some selection pressure on insect populations to develop resistance
     • Due to short life cycles resistance spreads quickly through a whole population
   • Resistance is developed due to
     • Breakdown of insecticide using enzymes
     • Modification of target receptor proteins on cell membranes

4. Pre-adaptation

   • Pre-adaptation = when an organisms pre-existing trait is advantageous to a new situation
     • This may help predict future resistance

5. Peppered moth

   • Due to an increase in pollution in the 19th century moth's with then allele for a darker colour were more camoflaged
     • This increases its chances of survival and reaching reproduction age
       • The gene is then passed on - overtime more moths become darker

6. Flavobacterium

   • Most evolution occurs as a result of negative selection pressures
   • However flavobacterium have evolved due to oppertunities that have arisen, they now digest nylon as a way of sustaining themselves