The main gameplay of CryptoKitties, beside collecting, is breeding. Breeding is influenced by both primary and hidden genes. While their are sire and matron roles, CryptoKitties can take on either role. After the cooldown from breeding, the matron will birth a new CryptoKitty and both kitties will be available for breeding again. Since each kitty can have a different cooldown, often the matron is the kitty with shortest cooldown and thus a new CryptoKitty is produced as soon as possible.
One of the first tools developed by the community were breeding calculators. These tools help predict the possibilities of certain outcomes based on the parent kitties genes.