Variation

• Differences between individuals

  presence of differences between individuals is called variation

  • while the two original cells (identical twins after mitosis) had same genetic information, the subsequent replication of DNA + cell divisions may have introduced changes to the DNA

  →also slight environmental differences in the womb or after birth can mean two individuals show physical differences
• Variation within species

  • almost any characteristics you will be able to find differences between members of the population

  →these differences are called intraspecific variation; the greater the genetic diversity, the greater the intraspecific variation
• Interspecific

  the variation that is used to separate members of one species from another

  →variation between species is called interspecific variation
• Intraspecific - Continuous Variation

  where there are two extremes + a full of range of intermediate values between those extremes

  • continuous variation is often regulated by more than one gene + can be influenced by the environment in which the organism lives

  examples :

  • height in humans
  • length of leaves of an oak tree
  • length of stalk (reproductive hypha) of a toadstool
  • number of flagella on bacterium
• Intraspecific - Discontinuous Variation

  when there are two or more distinct categories with no intermediate values

  • discontinuous variation is usually regulated by a single gene + is not influenced by the environment in which the organism lives in

  examples :

  • gender - mammals are either male or female, plants are male, female or hermaphrodite
  • some bacteria have flagella, but others do not
  • human blood groups - either A, B, AB, O group
• Causes of variation

  genetic

  • inherited from parents

  → the combination of alleles that we inherit is not the same as that in any other living thing (except identical twins)

  o we many share many alleles with other members but never a complete match

  →many of the approximately 20,000 genes, in human cells, may have more than one allele

  • the chances of any two individuals having exactly same combination of alleles is remote
• Causes of variation

  environmental

  • many characteristics can be affected by the environment

  → e.g. an overfed pet becomes obese

  an individual may contain a set of alleles, but environment may limit their expression (phenotype)
• Combined effects

  both genetically + environmentally

  • past century, humans have become taller due to better diet

  → however no matter how great your diet is, you’re less likely to grow taller if rest of your family are short

  • not all genes are active at any one time e.g. puberty, body changes as there are different genes activating

  →changes in the environment also directly affect which genes are active
• intraspecific variation

  difference between organisms of same species

  • produce fertile offspring
  • similar appearance
  • similar genetic makeup
• interspecific variation

  difference between organisms of different species