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Deviations From Mendelian Laws


Incomplete dominance (partial dominance or blended inheritance)

  • The concept of dominance is not universal. In some cases, expression of the dominant gene is incomplete or partial. Thus, in a cross involving such genes, there is incomplete dominance.
  • It was Carl Correns of Germany who discovered the incomplete dominance in the plant, Mirabilis jalapa (4-o’clock plant).
  • When a pure breeding red flowered plant is crossed with a pure breeding white flowered plant, all the F1 hybrids produced pink flowers (see Figure 12.6). This is because the dominant gene R responsible for red colour is not able to mask the recessive gene r completely.
  • When these pink flowered F1 hybrids are crossed among themselves, the F2 plants produce red, pink and white flowers in a ratio of 1 red:2 pink:1 white (1:2:1).

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