Reappearance of an ancestral trait after several generations because of recessiveness or masking effects is known as

The reappearance of an ancestral trait after several generations because of recessiveness or masking effects is known as Atavism.
An atavism is a modification of a biological structure whereby an ancestral genetic trait reappears after having been lost through an evolutionary change in previous generations.
Evolutionarily traits that have disappeared phenotypically do not necessarily disappear from an organism's DNA. The gene sequence often remains but is inactive. Such an unused gene may remain in the genome for many generations.