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.
The F1 is currently the most common cross, which is the poodle crossed with the bernese mountain dog. They are 50% poodle and 50% bernese mountain dog. This is a first generation hybrid and has what is known as the hybrid vigor.