What is the difference between a dominant and recessive trait?

A dominant trait is characterized by its ability to manifest in the phenotype whenever at least one dominant allele is present. This means that if an organism has one or two copies of the dominant allele, the dominant trait will be expressed. On the other hand, a recessive trait will only be expressed if the organism carries two copies of the recessive allele—one from each parent. This fundamental distinction between dominant and recessive traits is rooted in Mendelian genetics, where the presence of a dominant allele not only masks the effect of the recessive allele but also determines the observable characteristics of an organism.

Understanding this concept is crucial, as it forms the basis for predicting inheritance patterns in offspring. For example, in a genetic cross involving a dominant trait (like brown eyes) and a recessive trait (like blue eyes), any offspring with at least one allele for brown eyes will exhibit that trait, while those with two alleles for blue eyes will show the recessive trait. This principle is a key aspect of understanding how traits are passed down through generations.