Question at position 3 If two of the offspring produced in the previous question are crossed, what are the expected phenotypes of their offspring, and in what proportions?Full, green pods = 16 Full, yellow pods = 0 Constricted, green pods = 0 Constricted, yellow pods = 0Full, green pods = 0 Full, yellow pods = 0 Constricted, green pods = 0 Constricted, yellow pods = 16Full, green pods = 9 Full, yellow pods = 3 Constricted, green pods = 3 Constricted, yellow pods = 1Full, green pods = 4 Full, yellow pods = 4 Constricted, green pods = 4 Constricted, yellow pods = 4BlackTom题目解析

Question

Question at position 3 If two of the offspring produced in the previous question are crossed, what are the expected phenotypes of their offspring, and in what proportions?Full, green pods = 16 Full, yellow pods = 0 Constricted, green pods = 0 Constricted, yellow pods = 0Full, green pods = 0 Full, yellow pods = 0 Constricted, green pods = 0 Constricted, yellow pods = 16Full, green pods = 9 Full, yellow pods = 3 Constricted, green pods = 3 Constricted, yellow pods = 1Full, green pods = 4 Full, yellow pods = 4 Constricted, green pods = 4 Constricted, yellow pods = 4BlackTom题目解析

BlackTom AI · Accepted Answer

First, restating the problem in my own words: two offspring from the previous cross are mated, and we are asked to identify the expected phenotypes of their offspring and the correct proportions. The answer choices present four possible phenotype class tallies for pod color (green vs yellow) and pod shape (full vs constricted).

Option A: Full, green pods = 16; Full, yellow pods = 0; Constricted, green pods = 0; Constricted, yellow pods = 0.
- This option describes a single phenotype class making up all offspring. In a typical dihybrid cross with independent assortment and complete dominance, we expect multiple phenotype classes in a 9:3:3:1 ratio, not a single homogeneous class. Therefore, this option is inconsistent with Mendelian dihybrid expectations and is incorrect.

Option B: Full, green pods = 0; Full, yellow pods = 0; Constricted, green pods = 0; Constricted, yellow pods = 16.
- This is the exact opposite of Option A, again indicating all offspring fall into a single phenotype class (constricted, yellow). The same reasoning applies: a monomorphic outcome does not align with a dihybrid cross producing four phenotypic classes in a 9:3:3:1 proportion. This makes Option B incorrect.

Option C: Full, green pods = 9; Full, yellow pods = 3; Constricted, green pods = 3; Constricted, yellow pods = 1.
- This pattern matches the classic phenotypic ratio of a dihybrid cross with complete dominance, 9:3:3:1. Here, the four classes are present in the expected proportions: 9 offspring with full green pods, 3 with full yellow pods, 3 with constricted green pods, and 1 with constricted yellow pods. This aligns with independent assortment of two genes, each with complete dominance, producing two phenotypes per gene and their combinations.

Option D: Full, green pods = 4; Full, yellow pods = 4; Constricted, green pods = 4; Constricted, yellow pods = 4.
- This option shows equal counts for all four phenotypes (4 each), suggesting a 1:1:1:1 ratio. While this might occur in some genetic scenarios (for example, certain gene dosages or random sampling under constraints), it does not reflect the classic dihybrid 9:3:3:1 expectation under independent assortment with complete dominance. Therefore, this choice is not correct for the described cross.

To summarize the reasoning across all options: Options A, B, and D fail to reproduce the established four-phenotype ratio expected from a dihybrid cross with independent assortment and complete dominance. Only Option C provides the standard 9:3:3:1 distribution, matching the typical genetic outcome for such crosses. The key misconception in A and B is treating the cross as yielding a single phenotype; in D, the equal 4:4:4:4 distribution contradicts the 9:3:3:1 expectation. The correct understanding is that two independently assorting genes with two phenotypes each produce four phenotypic classes in the 9:3:3:1 ratio, as shown in Option C.

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