Question

how can a wildlife called as "gene Bank"

Answer 1

genetic material is frozen and thawed may vary from species to species.

Answer 2

Gene banks are a type of biorepository which preserve genetic material. For plants, this could be by freezing cuttings from the plant, or stocking the seeds (e.g. in a seedbank). For animals, this is the freezing of sperm and eggs in zoological freezers until further need.