In the F1 generation of 915 pea plants, tall is dominant over short. What was the parental cross?

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Study for the 9th Grade Biology SOL Test. Prepare with flashcards and multiple choice questions, each featuring hints and explanations. Get ready for your exam!

Multiple Choice

In the F1 generation of 915 pea plants, tall is dominant over short. What was the parental cross?

Explanation:
The trait tall being dominant means you only need one T allele for a tall plant. To get every F1 offspring tall, each zygote must receive a tall allele from one parent and a short allele from the other, which happens when the parents are pure-breeding for opposite traits: one parent is TT and the other is tt. Crossing TT with tt gives all offspring as Tt, so all are tall despite being heterozygous. If both parents were heterozygous (Tt x Tt), you would expect a mix of offspring: some tall (TT and Tt) and some short (tt). That would not produce an F1 generation consisting entirely of tall plants. So the parental cross that would yield all tall F1 offspring is a cross between a true-breeding tall plant and a true-breeding short plant.

The trait tall being dominant means you only need one T allele for a tall plant. To get every F1 offspring tall, each zygote must receive a tall allele from one parent and a short allele from the other, which happens when the parents are pure-breeding for opposite traits: one parent is TT and the other is tt. Crossing TT with tt gives all offspring as Tt, so all are tall despite being heterozygous.

If both parents were heterozygous (Tt x Tt), you would expect a mix of offspring: some tall (TT and Tt) and some short (tt). That would not produce an F1 generation consisting entirely of tall plants. So the parental cross that would yield all tall F1 offspring is a cross between a true-breeding tall plant and a true-breeding short plant.

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