Final answer:
A dominant trait is expressed when there is at least one copy of the dominant allele present, while a recessive trait is only expressed when two copies of the recessive allele are present.
Step-by-step explanation:
Dominant Trait vs. Recessive Trait
In genetics, traits are determined by alleles, which are different forms of a gene. A dominant trait is one that is expressed when there is at least one copy of the dominant allele present. It masks the expression of the recessive allele. On the other hand, a recessive trait is only expressed when two copies of the recessive allele are present. It is masked by the presence of a dominant allele.
For example, in pea plants, the color trait is controlled by two alleles: dominant allele (Y) for yellow color and recessive allele (y) for green color. If a plant has at least one copy of the dominant allele (YY or Yy), it will have yellow color, because the dominant allele masks the expression of the recessive allele. Only if a plant has two copies of the recessive allele (yy) will it have green color, as the recessive allele is not masked by any dominant allele.
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