Kaplan Nursing Entrance Practice Exam

Which of the following best describes a recessive trait in a genetic cross?

1. A trait that only appears in the homozygous condition

2. A trait that is always expressed in the phenotype

3. A trait that masks the expression of another trait

4. A trait that may be expressed in a heterozygous condition

The correct answer is: A trait that only appears in the homozygous condition

A recessive trait is one that is expressed only when an individual is homozygous for that trait, meaning that both alleles are the same and recessive. In the context of genetic crosses, this means that for a recessive trait to manifest in the phenotype (the observable characteristics), both alleles inherited from the parents must be the recessive form. For example, if we consider a trait such as flower color, a plant might carry two alleles for this trait: one dominant and one recessive. The dominant allele, when present, will overshadow the recessive allele, and the flower will display the dominant color. Only when the plant inherits the recessive allele from both parents will the recessive color be expressed. This understanding distinguishes recessive traits from dominant traits, which can be expressed even when only one copy is present. Therefore, the description of a trait that is only apparent in the homozygous condition accurately captures the essence of what makes a trait recessive.