Humber Admissions Practice Test

What is a characteristic of a dominant allele?

1. It is only expressed in homozygous conditions

2. It masks the effect of a recessive allele

3. It can only be inherited from one parent

4. It never appears in the phenotype

The correct answer is: It masks the effect of a recessive allele

A dominant allele is characterized by its ability to mask the effects of a recessive allele when both are present in an organism. This means that if an individual has at least one copy of a dominant allele, the phenotype (observable characteristics) associated with that allele will be expressed, regardless of the presence of a recessive allele. This characteristic is fundamental to the principles of Mendelian genetics, where dominant traits can be identified and understood through the study of inheritance patterns. In contrast to the other choices, the idea of being expressed only in homozygous conditions applies to recessive alleles, not dominant ones. Additionally, a dominant allele can be inherited from either parent, not just one, and it always influences the phenotype when present, ensuring it does appear in the phenotype. Therefore, the ability of a dominant allele to mask the presence of a recessive allele is a key feature that defines its nature in genetic inheritance.