The different types of Variation.
- one species differs from another species.
- 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.
- Taking measurements from a selected proportion of the population
- These should be, in theory, a true representation of the species we are measuring.
Non-representative data. Reasons why.
Sometimes a sample may not be representative of the whole population, this can be down to two main factors:
- 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.
- 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.
Factors affecting variation.
- sudden changes in the species will be passed on to offspring.
- 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