GCSE AQA Biology Evolution and Variation

Discontinuous variation is controlled by genes alone                                                                           e.g. nose shape, eye colour

Continous variation is inherited but can be changed by environment                                                   e.g. weight, finger length

Acquired characteristics are caused only by the environment                                                              e.g. piercings, tattoos

If there is a change in DNA then this is called a mutation and produces new characteristics.

How dogs became domesticated using selective breeding

• Wolf
• Possible some puppies were taken by humans, possibly trained
• Animals with desired features are selected by humans
• Selected are bred and reproduce 
  • Offspring with less desirable characteristics are not allowed to breed
  • Offspring with desirable characteristics are kept (selected)
• Repeated until domesticated dogs are achieved

Benefits  /  Risks

• Sales increase
• Dogs bred for specific jobs so the jobs get done better
• Gets rid of negative traits e.g. aggressive
• With a scientific approach, eradication of genetic diseases
• Improved food yield, crop quality
• INCEST - deformities, health problems
• Expensive
• Large amounts killed
• Reduces genetic diversity

There is variation in  a population, some variation is inherited

Reproduction results in many offspring, most of these do not survive

Occasionally there is a new variation, a mutation in the DNA

Only the fittest survive and reproduce, genes are passed on

Gradually a species can change and a new species will arise

New species will occur when two populations are separated

Variation - there is a genetic variation in a population

Mutation - random, the source of a new variation

Survival - of the fittest

Reproduction - the survivors pass on their genes 

Alleles - forms of a gene for fitness that are passed on

Lamark: 'Inheritance of acquired characteristics'                                                                                                animals evolved to suit their environment                                                                                            e.g. giraffes evolved to have longer necks to reach the leaves by stretching them

Darwin: 'The Theory of Evolution'                                                                                                                      natural selection, all animals have one common ancestor, survival of the fittest                                  e.g. the SouthAmerican rhea

Wallace: 'The Theory of Evolution'                                                                                                                      the weakest animals die out, the poorest adapted animals                                                                  e.g. finches

1. Fossils - evidence of extinction, gradual change (e.g. horse), possible to create a timeline

2. Embryology - embryonic development of animals is very similar, suggests relation and a      common ancestor

3. Selective breeding - Darwin's study of pigeons

4. Finches etc on Galapagos, Barnicle variation

5. DNA - found in all living things

6. Genetics - discovered by Mendel

7. Case studies - e.g. Peppered Moth

8. Antibiotic resistance in bacteria

1. An animal dies - if underwater their body sinks

2. The soft parts decompose, the hard parts (e.g. shell, bone) remain

3. It is covered in layers of sediment which settle in layers around/on top of the remains

4. These layers compress/are put under pressure

5. An impression is made 

6. Mineralisation - the bone/shell is converted to stone/rock