Answer:
Two, usually
Explanation:
A diploid plant has two copies (alleles) of every gene. If one copy of the gene is destroyed by a mutation, the plant will likely be okay with its other copy, and the trait will still be expressed.
However, some traits require both copies of the gene to be expressed. For example, if one gene is destroyed that means only half the amount of the gene product is produced. If that is not enough protein for the trait to be expressed, then the trait will be lost.
