When a plant with red flowers (c rc r) is crossed with a plant that has white flowers ( c wc w), the resulting offspring has pink flowers ( c rc w). if two pink flowers are crossed, what is the probability of having a white flower?

If a plant with red flowers is crossed with a plant with white flowers and the resulting offspring have pink flowers, this is incomplete dominance. So the red flowered plant is RR and the white flowered plant is rr and the pink plant is Rr. If two pink flowered plants are crossed, that is RrxRr. The resulting offspring are: 1:RR, 2: Rr, 1: rr. There are 1/4 or 25% white flowered plants. 

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