Phenomenon in biology that two types of pollen grains (carrier of allele "A" and "a" respectively) form pollen tubes that grow through the style of the flower with different speed. The effect of certation becomes obvious when a plant breeder makes reciprocal crosses between a heterozygous hybrid and a homozygous recessive plant; in that case certation causes different segregation results in both crosses.
BT: non-Mendelian inheritance
RT: incompatibility ↔ incongruence