What kind of crossing is necessary to prove the purebredity of a black (A) hornless (B) bull?

1) It is necessary to carry out an analyzing crossing. Cross a bull with a red horned cow – a recessive digomozygote.
2) If the resulting offspring are 100% black hornless, it means that the bull is a purebred (AABB), if the offspring is split, at least for one trait – the bull is not a purebred.

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