If you wanted to obtain 100% roan calves, then it si required to cross parents who are homo-zygous (pure lines) for the genes associated with this trait.
What is a homo-zygous individual?
A homo-zygous is an individual who has the same gene variants or alleles for a given gene locus.
Conversely, a heterozygous is an individual who has different gene variants or alleles for a given gene locus.
In breeding, pure lines (or purebred) are homo-zygous individuals that may be crossed to obtain the desired trait in the descendence.
Learn more about homo-zygous individuals here:
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