Investigating Variation.

• INTERSPECIFIC:
  • one species differs from another species.
• INTRASPECIFIC:
  • when members of the same species differ

Even identical twins, who are born with the same DNA, vary as a result of their different experiences.

Why is it so difficult? 

• It is difficut to make measurements as a Biologist because they are usually measuring some aspect of a living thing, and all living things differ from each other. 

• They cannot measure every member of the species in question, so they take samples.

• They make averages and conclusions from this data.

SAMPLING:

• Taking measurements from a selected proportion of the population

• These should be, in theory, a true representation of the species we are measuring. 

Sometimes a sample may not be representative of the whole population, this can be down to two main factors:

Sampling Bias:

• Where the selection process may be biased. Eg. throwing quadrates in another direction to nettles.
• We reduce sample bias by:
  • making the study area into a grid,
  • generate random numbers on a computer
  • take samples at the intersection of the co-ordinates.
  • Chance:

• Even if samping bias is avoided, the individuals chosen may, intentionally or unintentionally, not be representative.
• To reduce chance we:
  • use a larger sample to gain a more reliable result
  • use statistical tests to work out the pobability that chance will influence the data.

Genetic differences:

• Mutation
  • sudden changes in the species will be passed on to offspring.
• Meiosis
  • special form of nuclear division forms gametes. This mixes up the genetic material before its passed into the gametes, all of which will be different.
• Fusion of gametes
  • in reproduction, offspring inherit some of different from both when gametes fuse its a random process which adds to the variety of offspring the parents can produce.
• Asexual reproduction

Environmental influences