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Plant Reproduction Mitchell and Emma are senior students that share a biology class. Their high school has a section on school property that has been used to grow various plants over the years. Each student is required to select a plant to study for their final project. The pictures show some of the plants that are grown on school property. The tulips, irises, and daffodils reproduce asexually. The snapdragons and the roses reproduce sexually. Mitchell is interested in the snapdragons that reproduce sexually. He knows that purple (P) is dominant to white (w). Mitchell crosses a homozygous purple plant with a homozygous white plant. If he breeds two of the first generation offspring together, what percentage of the second generation offspring can Mitchell predict will most likely be white? a 25% b 50% c 75% d 100%

1 answer

To solve the problem, we can use a Punnett square to determine the genotypes of the offspring from the crosses.

  1. Initial Cross: Mitchell is crossing a homozygous purple snapdragon (PP) with a homozygous white snapdragon (ww).

    • The possible gametes from the PP parent are all P (since it is homozygous).
    • The possible gametes from the ww parent are all w (since it is also homozygous).

    Therefore, when we make the cross:

    \[ \begin{array}{|c|c|c|} \hline & P & P \ \hline w & Pw & Pw \ \hline w & Pw & Pw \ \hline \end{array} \]

    All first-generation offspring (F1) will have the genotype Pw, which are all purple flowers since purple (P) is dominant over white (w).

  2. Second Generation Cross: Now, Mitchell breeds two of the F1 offspring together (Pw x Pw):

    • The possible gametes from each Pw parent are P and w.

    To find the genotypes of the F2 generation, we make another Punnett square:

    \[ \begin{array}{|c|c|c|} \hline & P & w \ \hline P & PP & Pw \ \hline w & Pw & ww \ \hline \end{array} \]

    From this Punnett square, we can see the genotypes of the F2 generation:

    • PP (purple)
    • Pw (purple)
    • Pw (purple)
    • ww (white)

    The ratios of the genotypes are:

    • 1 PP
    • 2 Pw
    • 1 ww

  3. Calculating Percentages: Out of a total of 4 offspring (1 PP + 2 Pw + 1 ww), 1 offspring is white (ww).

    Therefore, the percentage of the second generation offspring that will most likely be white is:

    \[ \frac{1 \text{ (ww)} }{4 \text{ (total)}} \times 100% = 25% \]

The answer is a 25%.