A "single cross" is another name for an F1 hybrid. When two IBLs are crossed the F1 hybrid, or single cross, is the result. This type of cross has the most uniformity and hybrid vigor which makes it the best choice for the home gardener.
A "double cross" is made by crossing two single crosses which come from four separate IBLs. A double cross will be somewhat more variable than a single cross, but will have a wider range of adaptability. This adaptability makes the double cross good for diverse indoor environments.
The "top cross" and the "three way cross" are used as testers. A top cross is an IBL crossed with a variety, and it is used to test for general combining ability.(Ed.note:Only GCA can be found in a topcross.SCA is not sought because one half of the topcross is from a single genotype and the other half is from mixed gametes,therefore,one gene donor is unspecified.) A three way cross is an IBL crossed with an F1. The result of this cross will be one of the parents of the double-cross, and it is used to test for specific combining ability.
A "backcross" is crossing the progeny back to one of its parents,and on another level, to any plant with the same genotype as a Parent. It is designed to improve the parent by retaining most of its qualities and adding a new one. After a series of backcrosses,some degree of uniformity is realized as a result of increased gene frequencies,fixing of some loci through selection and some incidental homozygosity. However, the offspring can only become completely homozygous if the recurrent parent was completely homozygous,and will remain heterozygous for the loci that were heterozygous in the recurrent parent.
A "self cross" is the result of a female Cannabis plant pollinating herself, whether by artificial induction or natural hermaphrodite tendencies. A female that has produced seed from its own pollen is said to be the S0 generation and the resulting seeds are the S1 progeny.
A "full sib" cross is a straight male-female cross between brothers and sisters.
A "half sib" cross uses sister females and unrelated males.