A. The gene for the toxic compound was inherited from an ancestor of the plant population.
B. A mutation during DNA replication, prior to meiosis, resulted in a DNA sequence that codes for the compound.
C. The enzyme needed to produce the compound was transferred by a plant from another population.
D. Individuals in the plant population mutated in response to the pressure from herbivores. Markscheme
参考答案:
B
本题详细解析:
The appearance of new traits in a population can only occur if the genetic sequence for the trait is introduced to the population. Novel genetic sequences can result from several processes, one of which is through random mutations that occur during DNA replication. If the mutated DNA sequence codes for a functional protein product, it can produce a new trait in the offspring. If the trait is beneficial, the offspring will be more likely to survive and reproduce than other individuals in the population, and so the gene sequence for the trait will increase in frequency in the population.
In the case of the plant population, the ability to secrete a toxic compound could initially occur if a mutation during DNA replication resulted in a DNA sequence that codes for the compound (Choice B). Since this trait would likely be beneficial, as it protects against herbivores, it would likely increase in frequency over time until the entire population expresses the trait.
Choice A is incorrect because if the gene had been inherited from an ancestor of the population, the population would have always had the ability to secrete the toxic compound, rather than having no resistance to herbivores.
Choice C is incorrect because enzymes (proteins) cannot be transmitted between generations, so the receipt of an enzyme by one individual would have no effect on the ability of future generations to produce the toxic compound.
Choice D is incorrect because mutations are random, not directional. An organism cannot mutate its DNA in response to an environmental pressure. However, random mutations do sometimes occur which result in a selective advantage when selection pressures change.
