All sharingan users we have seen thus far are male. Which in my onpinion means its only a dominant trait for male Uchiha's. Any woman Uchiha would only be a carrier for said trait, which means to increase the probability of getting the Sharingan you would have to inter-breed which would cause deformities. The other option would be to mate outside Uchiha blood, which would weaken the sharingan because each new generation would be half the uchiha as the previous.
Som my question to you is how did the sharingan remain so strong?
Som my question to you is how did the sharingan remain so strong?