How many dominant alleles MUST be present for the dominant trait to show up?

one

Explanation:

"Dominant traits only require one allele to be present in order for the trait to be expressed, while recessive traits must have both alleles present in order for the trait to be expressed." I HOPE IT HELPS:)

Only one dominant allele must be present.

Explanation:

The reason they are called dominant is because if they are present, then that is the trait that shows up.

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