Origin
In most sheep, a white fleece is not albinism but a dominant gene that actively switches color production off, thus obscuring any other color that may be present. As a result, a black fleece in most sheep is recessive, so if a white ram and a white ewe are each heterozygous for black, in about 25% of cases they will produce a black lamb. In fact in most white sheep breeds only a few white sheep are heterozygous for black, so black lambs are usually much rarer than this.
Read more about this topic: Black Sheep
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