The main focus here is the unique set of 6 genes that each CAThlete has: muzzle, arms, body, tail, ears, environment. When 2 CAThletes are bred, the offspring may inherit traits from one of its parents, or get a new one as a result of mutation. This applies to each of the 6 genes: for each gene, there is a chance of taking after one or the other parent, or having a completely new one from mutation.
Below is the inheritance probability per level table, showing the percentage of possible genetic contribution of each parent as well as mutation:
The inheritance probability is calculated per each parent. That means that if a level 6 CAThlete is bred with level 9 CAThlete, the inheritance probability of their genes is calculated separately, applying the corresponding percentages for level 6 and for level 9.
Mutations rate. There are 5 rarity categories in Walken: common, uncommon, rare, epic, legend. For levels 6, 7, 8, there is a mutation rate applied that lowers the rarity of the resulting genes inherited by the offspring in case of mutation. At levels 9 and 10, the rarity of the mutating genes is not affected by the mutation rate. For example, the maximum rarity of genes that can be passed down to an offspring by a 6-level rare CAThlete in case of mutation would be common since the -3 mutation rate is applied.