Variation

Biology AQA new AS level unit 2 variation

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Investigating 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.
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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.

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.
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Types of Variation.

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.
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