It tells you what the paragraph is going to be about.
An F1 hybrid (or filial 1 hybrid) is the first filial generation of offspring of distinctly different parental types. F1 hybrids are used in genetics, and in selective breeding, where it may appear as F1 crossbreed. The term is sometimes written with a subscript, as F1 hybrid.
Hybrid cannabis strain is created out of two different pare nt strains genetically. For better understanding, when you happen to mix and cross two unlikely IBL cannabis strains for the very first time, you will produce F1 generation and when you cross two F1 breed, it will produce an F2 generation.