Passage IV

Four students observed that in a population of land plants, Population A, a plant could have a green stem or a purple stem. Each student proposed an explanation for this observation.

Student 1

All plants in Population A produce the green pigment chlorophyll. If a plant receives 8 hr or more of sunlight each day, it also produces a purple pigment, causing its stem to be purple. If a plant receives less than 8 hr of sun­light each day, it does not produce this purple pigment, so its stem is green. All plants in Population A are genetically identical, so they all have the ability to produce both pigments.

Student 2

All plants in Population A produce the green pigment chlorophyll. If a plant receives too little phosphorus (a nutrient), it also produces a purple pigment, causing its stem to be purple. If a plant receives enough phosphorus, it does not produce this purple pigment, so its stem is green. All plants in Population A are genetically identical, so they all have the ability to produce both pigments. The amount of sunlight received by a plant does not affect stem color.

Student 3

All plants in Population A produce the green pigment chlorophyll. The production of purple pigment is deter­mined by Gene Q, which has 2 alleles (Q and q) and 3 pos­sible genotypes (QQ, Qq, and qq). A plant with either the Gene Q genotype QQ or the Gene Q genotype Qq produces the purple pigment, causing its stem to be purple. A plant with the Gene Q genotype qq does not produce this purple pigment, so its stem is green. The amount of sunlight or nutrients received by a plant does not affect stem color.

Student 4

All plants in Population A produce the green pigment chlorophyll. The production of purple pigment is deter­mined by Gene Q, which has 2 alleles (Q and q) and 3 pos­sible genotypes (QQ, Qq, and qq). A plant with the Gene Q genotype qq produces the purple pigment, causing its stem to be purple. A plant with either the Gene Q genotype QQ or the Gene Q genotype Qq does not produce this purple pigment, so its stem is green. The amount of sunlight or nutrients received by a plant does not affect stem color.

24. Suppose 2 of the purple-stemmed plants in the popu­lation were crossed and 52 purple-stemmed and 15 green-stemmed offspring were produced. If all the parents and offspring in the cross were grown under the same conditions, these results would best support the explanation of which student?

Answer and Explanation

Your Answer is

Correct Answer is H

Explanation

First of all, it grows in the same environment but has different colors, then 12 cannot be correct, and then there is less green in the offspring, which shows that green is a recessive trait, which is consistent with the point of view of 3