Evolution: Variation

Evolution: Variation

1. Differences within a species

2. Caused by: organisms genes or environment

3. Genetic Variation

   • Differences between organisms due to their genes
   • Alleles: differences in genes for particular characteristics.
     • Meiosis & fertilisation produce new combinations of alleles
       • Possible to have completely new alleles form sometimes
         • Happens when a mistake is made as DNA is being replicated e.g a missing nucleotide, an extra nucleotide or a nucleotide replacing another

4. In sexual reproduction, alleles are shuffled around, each time a new organism is produced there is more chance of variation (More than in a plant) because in principle any male gamete can fuse with any female gamete

   • Gives an almost infinite number of combinations of possible variations

5. Environmental Variation

   • Differences between organisms due to the environment
     • 2 people with the same alleles to make them tall but have very different diets can be very different heights
       • 2 plants with identical genes can be a different size due to one being in the shade & the other being in the sun
   • Can arise throughout the lifetime but can not be inherited as it is not caused by DNA

6. Discontinous Variation

   • Variation where each organism belongs to one of a few clearly defined groups
     • E.g Human ABO Blood Groups: A, B, AB, O. No in-betweens
     • Almost always caused by genes, with little or no environmental influence
       • Usually just 1/2 genes involved each having only a few alleles e.g Human ABO blood groups are controlled by a single gene with 3 alleles
   • Continous Variation
     • Variation where there is a continuous range of values between 2 extremes
       • E.g eye or human skin colour is impossible to categorise in clearly defined colours
         • E.g Oxford Ragwort leaf length can range between 2mm to 180mm, any length between those values is possible
     • May be caused by genes, environment or both
       • E.g human eye colour is genes
         • Skin colour can be both due to how much exposure to sunlight
           • Leaf length is environmental due to how much sunlight they get
     • Most variations in humans is continuous influenced by genes & environment