Even is the english lines have some minorca inside them, they are pure, because the PURPOSE was to be pure and to have the right balance between showing and producing. Also, bear in mind that the TERMINAL CROSSES sold to us from the big companies lack many of the qualities to be excellent parent stock. That's why geneticists call them T E R M I N A L crosses. But, you can use them for hatching your own WL for 1-3 generations. You can achieve feather sexing only if you hatch terminal crosses selected carefully for the feather sexing purpose.