Humber Admissions Practice Test

A dominant allele is one that will always express its trait in the presence of another allele, making it the correct choice. When an individual has at least one dominant allele, its expressed trait will be visible, overshadowing the effect of any recessive allele present. This characteristic is foundational in understanding Mendelian genetics, where dominant alleles are represented by uppercase letters and recessive alleles by lowercase letters.

For context, a recessive allele requires two copies (homozygous recessive) to express its trait, so it does not show when paired with a dominant allele. Homozygous recessive refers specifically to an individual with two recessive alleles, which also does not directly relate to the inquiry about which allele exhibits its trait in the presence of another. Heterozygous describes an individual with one dominant and one recessive allele; while it could express the recessive trait if both alleles were recessive, the presence of the dominant allele prevents the expression of the recessive trait. Therefore, understanding the defining properties of dominant alleles clarifies their unequivocal expression in a genetic pairing.