Until that time, the cremaster muscles can retract immature testicles into the groin. Cryptorchidism refers to the failure of one or both testicles to descend into the scrotum and remain there by 7 to 8 months of age. While unilateral cryptorchidism is most common, it can be bilateral. The mode of inheritance is suggested to be recessive and polygenic, and cryptorchid males should not be used for breeding. Unilateral cryptorchid males may be fertile and so should be castrated.
Cryptorchidism is an example of a sex-limited trait.
The trait is physically expressed only in the male even though it can be carried by females. Both the sire and dam of an affected cat should be considered to be carriers. Some full siblings of an affected cat will also be carriers. A reduction in the number of cryptorchid cats in a breeding program can be achieved by removing affected males and carrier parents from breeding. If the problem is widespread in a family line, full siblings of an affected cat should also be eliminated from the breeding program.