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Why is a testcross unnecessary to determine whether a snapdragon with red flowers is homo- zygous or heterozygous?

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Final answer:

A testcross is not needed to determine if a snapdragon with red flowers is homozygous or heterozygous due to incomplete dominance, where heterozygous snapdragons exhibit pink flowers.

Step-by-step explanation:

A testcross is unnecessary to determine whether a snapdragon with red flowers is homozygous or heterozygous due to the phenomenon of incomplete dominance in its flower color inheritance. In snapdragons, a cross between a homozygous red-flowered plant and a homozygous white-flowered plant yields heterozygous offspring with pink flowers, indicating the expression of both alleles in an intermediate phenotype. Hence, a red-flowered snapdragon plant can only be homozygous, as a heterozygous plant would exhibit pink flowers, not red. This is why a testcross, which is typically used to discern between a homozygous dominant and a heterozygous dominant phenotype, is not necessary in this case.

User ROBERT RICHARDSON
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