The original idea of coupling implied that there was actually some undefined force that kept two dominant alleles from two different genes together during the process of gamete formation. Thus the gamete containing the dominant alleles A & B (and its counterpart gamete ab) deviated from independent assortment. This coupling could be partial or complete. In 1911 Bateson and Punnett discovered gametes with one dominant and one recessive allele (i.e., Ab & aB). These they called repulsion gametes.

Coupling refers to the case where dominant alleles are on the same homologue chromosome and both recessive alleles are on the other homologue chromosome. Thus, the parental gametes are AB and ab. Some authors call this cis. Repulsion refers to the case where each homologous chromosome has one dominant and one recessive allele from the two genes. Thus, the parental gametes are Ab and Ab. Some authors call this Trans.