In a diploid organism, an allele that must be present in two copies to be expressed is called?

• A. Dominant
• B. Recessive
• C. Genotype
• D. Phenotype

Answer: (B)

In diploid organisms, genes come in pairs, so how a trait shows up depends on whether an allele is expressed when paired with another allele. An allele that must be present on both chromosomes to affect the phenotype is a recessive allele. When one recessive and one dominant allele are present, the dominant allele usually masks the recessive one, so the trait associated with the recessive allele isn’t seen. Only when the organism has two copies of the recessive allele do you observe the recessive trait. This is different from the genotype, which is simply the pair of alleles an individual has, and the phenotype, which is the outward trait you observe.