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Biology  /  Bio 1037  ·  Atom · ~20 seconds

The Testcross

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A testcross crosses an unknown genotype, showing the dominant trait, against a homozygous recessive individual to reveal whether it is homozygous or heterozygous.

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A testcross producing only dominant offspring indicates a homozygous dominant parent; a roughly even split indicates heterozygous.

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A small testcross litter showing only the dominant trait does not rule out a heterozygous parent — larger samples resolve the ratio.