Kaplan Nursing Entrance Practice Exam

Which sentence accurately reflects the concept of a dominant allele?

1. A dominant allele is never masked.

2. A dominant allele can be present in only one copy to express a trait.

3. A dominant allele must be homozygous to be beneficial.

4. A dominant allele will always determine the phenotype.

The correct answer is: A dominant allele can be present in only one copy to express a trait.

The choice that highlights the key characteristic of a dominant allele is that it can be present in only one copy to express a trait. This means that if an individual has one dominant allele for a particular gene, that dominant trait will be expressed in the phenotype, regardless of whether the other allele is dominant or recessive. This principle is essential in understanding inheritance patterns in genetics. Dominant alleles require just one copy to manifest the dominant trait, which is why they can override the effects of a recessive allele, leading to the expression of the dominant phenotype. In contrast, other statements do not accurately capture the essence of how dominant alleles work. For instance, stating that a dominant allele is never masked suggests an absolute rigidity that does not consider the presence of interactions with other alleles or varying environmental influences. Saying that a dominant allele must be homozygous to be beneficial implies that it does not have functional effects as a single copy, which contradicts the definition of dominance itself. Lastly, indicating that a dominant allele will always determine the phenotype oversimplifies how traits can be influenced by multiple alleles or other factors beyond simple dominance. Understanding that a dominant allele requires only one copy for a trait to be expressed is crucial for studying inheritance