Question

in pea plants, tall plant height is dominant over short plant height. if there are 200 short plants in the f2 generation from a cross that followed mendel’s methods, about how many plants will be tall in that generation?
200
300
600
1,000

Explanation:

Step1: Recall Mendel's ratio

For a monohybrid cross (tall vs short in pea plants), the phenotypic ratio in F2 generation is 3 (tall) : 1 (short). So the ratio of tall to short plants is 3:1.

Step2: Set up proportion

Let \( x \) be the number of tall plants. We know that \(\frac{\text{Tall}}{\text{Short}}=\frac{3}{1}\), and short plants = 200. So \(\frac{x}{200}=\frac{3}{1}\).

Step3: Solve for \( x \)

Cross - multiply: \( x = 3\times200=600 \)? Wait, no, wait. Wait, the total ratio parts are 3 + 1 = 4. Wait, no, the ratio of tall to short is 3:1. So if short is 1 part = 200, then tall is 3 parts. Wait, 3 parts would be 3×200 = 600? Wait, no, wait, maybe I messed up. Wait, no, the phenotypic ratio for monohybrid cross is 3 tall : 1 short. So number of tall plants = 3× number of short plants. Since short plants are 200, tall plants = 3×200 = 600? Wait, but let's check again. Wait, the ratio of tall to short is 3:1. So if short is 200 (1 part), tall is 3 parts. So 3×200 = 600. Wait, but let's confirm the ratio. In Mendel's experiments, for a monohybrid cross (like TT × tt, then F1 Tt, then F1 self - cross Tt × Tt), the F2 generation has genotypes TT:Tt:tt = 1:2:1, and phenotypes tall (TT + Tt) : short (tt)= 3:1. So yes, the ratio of tall to short is 3:1. So if short plants are 200 (1 part), tall plants are 3 parts, so 3×200 = 600.

Answer:

600 (corresponding to the option "600")