Revision: evolution (66 marks Paper 2) Artificial selection and Natural Selection

differences between these two processes.

- Organisms of a particular species/any example show a great deal of variation√

- Humans√/farmers/scientists select organisms

- with a particular desirable characteristic√

- and interbreed √ them

- with other organisms that also √ have the same desirable characteristic

- to improve this characteristic further √ in the offspring

- They may also choose organisms with different √ desirable characteristics

1. 
   Choose the animal or plants that have the best characteristics
   
2. 
   Breed them with each other
   
3. 
   Choose the offspring with the best combination of characteristics
   
4. 
   Allow them to breed with each other
   
5. 
   Repeat the procedure many times to improve the characteristics
   

• 
  Produced cattle with more meat
  
• 
  cows that give more milk
  
• 
  wheat that produces more seeds
  
• 
  sheep that produce more offspring
  

• 
  Usually closely related organisms are bred – leading to inbreeding
  
• 
  Inbreeding reduces the gene pool of a species
  
• 
  This could cause the entire species to be wiped out if exposed to a disease against which it has no resistance
  

- Most species produce a large number of offspring

- Some individuals may have characteristics such as small beak size √ that are favourable √

for the environmental conditions

- Others may have characteristics /any example that are unfavourable √

- These offspring compete √ with each other for food, shelter, etc.

- Offspring that have desirable features for obtaining these resources will survive √

- Selective pressure by the environment √ due to competition / changing environmental

conditions

- Organisms with favourable characteristics survive and reproduce √ to pass favourable

characteristics to their offspring √

- while organisms with unfavourable characteristics will die out √

- Over time the whole population will have this favourable trait √

- the gene pool of the population has changed √

• 
  Mutation
  
• 
  Meiosis : - independent assortment / crossing – over
  
• 
  Random mating
  
• 
  Chance fertilization
  

Question 2

Below is a sequence of diagrams (A, B and C) representing the changes

in a population of cactus plants on which bucks feed over a period of time.