Genetic Causes of Variation

Genetic cause of variationWhat happens?Why does it cause variation?Example?
AllelesDifferent versions of genesProduces different proteins and therefore different structures and effectsBlood group
MutationsMistake in DNAChanges in protein that are coded forCystic fibrosis
MeiosisGametes form which have half the genetic material of parent cells. Crossing over and independent assortment also occur to make every gamete genetically different.Different gametes have different mix of allelesVariation in gametes
Sexual reproductionInherit genes from both parentsIndividual produced is genetically different from parentsChildren
ChanceChance which gametes fertiliseUnique combination of genetic material for each offspringSiblings different from each other

Environmental Causes of Variation

Environmental cause of variationWhat happens?Why does it cause variation?Example?
Conditions for plantPlants in different conditions grow to different sizes Plants in different pH soils can grow different coloured flowers Lack of nutrients for plantMore sunlight for photosynthesis to make glucose for respiration and growth Acidic soil makes blue flowers. Alkali makes pink flowers ProteinsRose bush in higher light intensity grows bigger Different coloured flowers of hydrangeas Nitrates
Injury/DiseaseDamaged tissueDamages cell, leaves marks on skinScars

Combined Environmental and Genetic Causes of Variation

Environmental and genetic effect of variationHow do genetics play a part?How does environment play a part?
HeightInherited genes from parentsMalnourishment
Skin colourGenes instruct melanin levelsSunlight can increase melanin production

Discrete Variation

  • Discontinuous/discrete variation is normally only controlled by a single gene (or very few).
  • There are no in-between values, only specific ones.
  • Normally represented through a bar chart.

Continuous variation

  • A characteristic that can take any value in a range (quantitative) is said to show continuous variation.
  • Characteristics that show continuous variation such as height show a normal distribution pattern
  • These characteristics are usually controlled by a number of genes (polygenic) and influenced by the environment