👉 In genetics, an "opalotype" is a specific genetic marker used to identify and differentiate different species of organisms. It refers to a single DNA sequence that is unique to each organism in its own species. This characteristic makes it possible to distinguish between individuals by their appearance, behavior, and genetic differences. For example, in humans, the opalotype (also known as the X-chromosome) is the single X chromosome, which is found on the X chromosome of a sperm cell during fertilization