types of variation

• what are the two types of variation?

  • interspecific- variation between species
  • intraspecific- variation within species
• what are two main causal factors of variation?

  • genetic
  • environmental
• what are the causes of genetic variation?

  1. alleles- different forms of the same gene, produce different characteristics
  2. mutations- changes to the DNA base sequence, changes to genes, therefore changes to proteins coded for. This affects physical and metabolic characteristics
  3. meiosis- independent assortment of homologous chromosomes and crossing over- gametes of an individual show variation
  4. sexual reproduction- offspring produced differs genetically from each parent as characteristics inherited from each
  5. random fertilisation- different gametes combine each time-variation between siblings
• what is discontinuous variation?

  • characteristic that only results in certain values, no inbetween
  • determined purely by genetic factors
  • eg sex- male/female
  • qualitative
  • represented using bar chart, but pie chart can be used
  • usually monogenic (controlled by one gene)
• what is continuous variation?

  • can take any value within a range
  • polygenic (controlled by a number of genes)
  • eg- height and mass of plants and animals
  • influenced by environmental factors
  • data collected as a frequency table and then plotted as a histogram/curve is drawn (normal distribution curve)
• what are the characteristics of a normal distribution?

  • bell shaped curve
  • mean median and mode in the middle
  • 50% of values are less than the mean and 50% are greater

  
• state examples of environmental variation

  • plants- light, food available, water
  • scars on the body