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The causes of variation within a species are:

  1. Environment:
    • Various environmental factors like food, light, heat, etc. play an important role in somatogenic variations.
  2. Changes in genetic pattern:
    • Changes in the genetic pattern due to any factor results in some minor or major changes in the organism inheritable in the next generation.
  3. Crossing over:
    • Results in recombination of genetic pattern during meiosis.
  4. Dual parentage:
    • An organism developed from the zygote is formed as a result of fusion of male and female gametes (50% each from father and mother).
    • Mother and father also have dual parentage.
    • Hence, a child has 50% characters from parents, 25% from their grandparents and 25% from their great grandparents.
    • Thus, dual percentage plays a key role in variations.