Variation

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.

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.

Environmental Influences:

• 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.

Genetic Factors:

• Few distinct forms, no intermediate types e.g. blood group.
• Controlled by a single gene.

Environmental Influences:

• 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.