Nothing is different about sex-links as far as being able to reproduce. They will reproduce, but because they are hybrids, they won't necessarily reproduce themselves. In others words, a Red Star roo and a Red Star hen won't produce Red Star chicks. They might have characteristics of any of the constituent breeds that produce the Red Star, or they may actually look like Red Stars, or combinations of all of the above. When people say sex-links can't reproduce, what they mean is a sex-link is not a breed that can reliably reproduce itself by mating with its own kind like two barred rocks can, for instance. They are essentially mutts like any other crossbreed, but they have been bred for the specific male and female color and marking characteristics that allow you tell their sex by those colors and markings.
UGCM