People who don't:depends which one is the domiantant gene, if it was the sharingan and if the parent with the sharingan was Homozygous dominant and the other with the byakugan was homozygous recessive then all the ofspring would have the sharingan phenotype :/
there will be a chance that ...it will be 2/3 sharingan and 1/3 byakugan........or 2/3 byakugan and 1/3 sharingan ....or even .....1/3 mutated eye new power ...