Next, you perform a cross with a mouse with black fur and a mouse with white fur. Which result(s) for the offspring would confirm that the mouse with black fur was heterozygous?

White fur is recessive, so the white-furred mouse must pass on a recessive allele. If the black-furred parent were homozygous dominant, all offspring would have black fur. Any white offspring shows that the black-furred parent also passed on a recessive allele, confirming it was heterozygous; choices B, C, and D each include white offspring.

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