Variation, Mutation and Evolution

• Variation


  The differences found within the same species
• Causes of variation


  • Sexual reproduction
  • Environmental influences
• Individuals in a population are usually similar to each other, but not identical
• Genetic variation


  Variation caused by inheritance because of genes
• Environmental variation


  Variation caused by factors such as climate, diet, accidents, culture and lifestyle
• Genetic and environmental causes combined

  Features vary because of a combination of genetic and environmental causes
• Features that show environmental variation


  • Scar
  • Accent
  • Flower colour in hydrangeas
• Identical twins inherit exactly the same features from their parents, but if twin A eats more than twin B, twin A is likely to end up heavier
• Variation


  The differences found within the same species
• Causes of variation


  • Sexual reproduction
  • Environmental influences
• Continuous variation


  A characteristic that changes gradually over a range of values
• Characteristics with continuous variation


  • Height
  • Weight
  • Hand span
• Discontinuous variation


  A characteristic with only a limited number of possible values
• Characteristics with discontinuous variation


  • Gender (male or female)
  • Eye colour
  • Blood group
• Human beings have one of four blood groups: A, B, AB or O
• There are no intermediate values between the blood groups, so this shows discontinuous variation
• Variation


  The differences found within the same species
• Causes of variation


  • Sexual reproduction
  • Environmental influences
• Asexual reproduction


  Only one parent is needed, no fusion of gametes, offspring are clones
• Mitosis


  The process used in asexual reproduction to create identical copies (clones) of the parent cell
• Sexual reproduction


  Requires two parents, male and female, each producing gametes that fuse to form a zygote
• Gametes


  Sex cells (sperm in males, ova/eggs in females)
• Haploid


  Having half the total number of chromosomes (23 in humans)
• Diploid


  Having the full number of chromosomes (46 in humans)
• Zygote


  The fertilised egg cell
• As half the genetic make-up of the offspring is from one organism and half from another, it is genetically different from its parents, showing variation