Which genetic concept explains why a trait might disappear in one generation but reappear in the next?

The concept of recessiveness explains why a trait might disappear in one generation but reappear in the next. Recessive traits are expressed only when an individual has two copies of the recessive allele, often denoted as "homozygous recessive." In cases where an allele is recessive, it can be carried by individuals who are "heterozygous," meaning they possess one dominant allele and one recessive allele. These heterozygous individuals do not show the recessive trait themselves because the presence of the dominant allele masks the effect of the recessive one.

When two heterozygous individuals mate, there is a chance that some offspring will inherit two recessive alleles (one from each parent), which will allow the trait to be expressed again in that generation. Thus, a trait can be hidden in a generation when it is only carried by heterozygous individuals, then reappear in subsequent generations when the appropriate genetic combinations occur.

Other concepts, like codominance, epistasis, and incomplete dominance, describe different mechanisms of trait expression and inheritance, but they do not specifically address the ability of a recessive trait to seemingly vanish and then resurface in later generations.