F1

F1 ("filial 1," from Latin filius/filia, "son/daughter") is the first-generation offspring of a controlled cross between two genetically distinct, homozygous (true-breeding) parents, following Mendelian genetics (Mendel 1866; Acquaah 2012). In a proper F1, offspring are uniformly heterozygous at segregating loci and often express hybrid vigor (heterosis) — increased size, yield, or vitality exceeding either parent. For cannabis, a true F1 requires two homozygous inbred parental lines; most commercial cannabis "F1s" are actually polyhybrids between heterogeneous parents and therefore do not exhibit true F1 uniformity (Clarke & Merlin 2013; Lewis et al. 2018 emphasized Mendelian breeding for cannabinoid predictability). Crossing a Type I (B^T/B^T) parent with a Type III (B^D/B^D) parent yields uniformly heterozygous Type II (B^T/B^D) F1 offspring (de Meijer et al. 2003). → See also: F2, BX, IBL, Hybrid.