Question at position 4 Two pea plants are among the F1 offspring of a true-breeding violet flowering plant with full, green pods, and a true-breeding white flowering plant with constricted, yellow pods. What percentage of the F2 offspring will produce violet flowers with full, yellow pods?35%0%21%14%BlackTom题目解析

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Question at position 4 Two pea plants are among the F1 offspring of a true-breeding violet flowering plant with full, green pods, and a true-breeding white flowering plant with constricted, yellow pods. What percentage of the F2 offspring will produce violet flowers with full, yellow pods?35%0%21%14%BlackTom题目解析

BlackTom AI · Accepted Answer

We start by outlining the genetics of the cross. The parental phenotypes are violet flowers with full green pods, and white flowers with constricted yellow pods. This implies three traits that assort independently: flower color (violet vs white), pod shape (full vs constricted), and pod color (green vs yellow).

For each trait in the F1 generation, the dominant phenotype appears with a 3/4 probability and the recessive phenotype appears with a 1/4 probability in the F2 from a heterozygous cross (assuming independent assortment and rounding to simple Mendelian ratios):
- Flower color: violet is dominant over white. The F1 plants are heterozygous for color, so in the F2, violet flowers appear in 3 of 4 plants (probability 3/4).
- Pod shape: full is dominant over constricted. The F1 plants are heterozygous for shape, so full-shaped pods appear in 3 of 4 plants (probability 3/4).
- Pod color: green is dominant over yellow. The F1 plants are heterozygous for pod color, so yellow pods appear in 1 of 4 plants (probability 1/4).

We are asked for F2 offspring that have violet flowers (dominant color), full pods (dominant pod shape), and yellow pods (recessive pod color). Assuming independence among these three traits, multiply the probabilities:
- Violet flowers: 3/4
- Full pods: 3/4
- Yellow pods: 1/4
Product = (3/4) × (3/4) × (1/4) = 9/64 ≈ 0.140625, or about 14%.

Now consider the other options: 
- 35% would require a combination of probabilities that do not align with the 3/4, 3/4, and 1/4 product for these three distinct traits, so it misrepresents at least one trait’s likelihood.
- 0% would imply impossibility, which isn’t the case here since each trait has a nonzero probability in the F2.
- 21% corresponds to a different combination of trait probabilities and would not equal the exactly derived product for violet color, full shape, and yellow pod color.

Thus, the calculation that yields roughly 14% is the consistent Mendelian expectation for the described triple-trait cross in the F2. The remaining options do not match the independence-based product of the three trait probabilities.

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