Genetics Picture

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Incomplete dominance

The dominance of one allele over an other is not always complete. Sometimes one can distinguish a homozygotic individual from a heterozygotic one. One clear example of this one can find in the Four O-Clock flower, Mirabilis. Here the red color is incomplete dominant over the white. Heterozygotic flowers get at color in between red and white - they become pink. This is called incomplete dominance.

If one crosses a red and a white Mirabilis all the offspring will have pink flowers. If one crosses two pink flowers we get the following breeding chart:

_______________________________________
|    |              |                 |
|    | fr           |  fw             |
|____|______________|_________________|
|    |              |                 |
| fr | frfr         |  frfw           |
|    | red          |  pink           |
|____|______________|_________________|
|    |              |                 |
| fw | frfw         |  fwfw           |
|    | pink         |  white          |
|____|______________|_________________|

We then get the splitting ratio 1 red : 2 pink : 1 white - 1:2:1.

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