Put a duckwing (e+, wild type, as in brown leghorn (light)) male onto a barred female. take the barred male from this cross & put onto duckwing females. All things being equal about half of the offspring will be duckwing & about half of the offspring will be barred giving odds of about 1 in 4 being crele. In order to make bred true breed the crele offspring together, females will be fine but select for males wih two barring genes.