Interspecific Variation - 1 species differs from another.
Intraspecific Variation - members of the same species differ from one another.
Sampling- measuring individuals selected from population may not be representative due to: sampling bias - because of process or or unrepresentative choices; or chance.
- Random sampling:
- 1. Divide area into grid.
- 2. Use random co-ordinates.
- 3. Take samples at each point.
- Minimise sampling effect by:
- 1.Using large sample size - more reliable, less chance.
- 2. Analysis of data collected - determine extent chance has on data.
Causes of Variation.
Genetic Differences - change between generations and arise because of:
- Mutations - sudden changes in genes/chromosomes may be passed down.
- Meiosis - mixes up genetic material before passed to gametes.
- Fusion of gametes - offspring inherit characteristics from both parents and fuse randomly.
- Variation, in asexual only, increased by mutation. Sexual has 3 methods so more varied.
- Affects expression of genes.
- Genes set the limits but environment determines where within these limits an organism lies.
- Includes, climate, soil conditions, pH and food availability.
Types of Variation.
- Few distinct forms, no intermediate types e.g. blood group.
- Controlled by a single gene.
- Some characteristics grade into 1 another (continuum) e.g. height.
- Controlled by many genes (polygenes).
- Height depends on polygenes and environment.
Mean and Standard Deviation:
- Normal distribution curve differs in its max height and width.
- Mean - measures max height, provides average value and used in comparisons.
- Standard deviation - measures width, indicates range of values either side of mean. It is distance from point where curve changes from convex to concave.