Genes don't "exist"

Chromosomes exist, you can see them with a microscope. "Genes" are an abstraction. A gene is simply a section of a chromosome, but there is no objective dividing line between one gene and another. A gene can be split up ("chromosomal crossover") when the chromosome divides. A "gene" can refer to a deletion, an absence, where one person has no base-pair where one is normally found.