The rapid development of resistance to pesticides such as DDT in insect populations is an example of:

Question

BlackTom AI · Accepted Answer

Directional selection occurs when natural selection consistently favors individuals at one end of a phenotypic range, causing the population mean to shift toward that phenotype. Key concepts: variation in traits exists, heritability of resistance alleles, differential survival due to pesticide exposure, and change in allele frequencies across generations.

Step-by-step reasoning:
1. Initial genetic variation: assume a resistance allele R is present at low frequency (p = 0.10) and the susceptible allele r at q = 0.90.
2. Under Hardy-Weinberg, genotype frequencies are: RR = p^2 = 0.01, Rr = 2pq = 0.18, rr = q^2 = 0.81.
3. Pesticide imposes strong selection: suppose rr individuals mostly die (survival = 0), Rr survive at reduced rate (50%), and RR survive fully (100%).
4. Survivors’ proportions: RR = 0.01, Rr = 0.18 × 0.5 = 0.09, rr = 0.81 × 0 = 0. Total survivors = 0.10.
5. New allele frequency p' among survivors = [2( RR ) + (Rr )] / [2 × total survivors] = [2(0.01) + 0.09] / (0.20) = (0.02 + 0.09) / 0.20 = 0.11 / 0.20 = 0.55.
6. The resistant allele frequency jumps from 0.10 to 0.55 — a clear shift of the population toward the resistant phenotype.

Why this is directional selection: the pesticide consistently favors one extreme phenotype (resistance), increasing its frequency and shifting the population distribution in one direction.

Why other choices are incorrect:
- Stabilizing selection favors intermediate phenotypes and reduces extremes; it would not increase resistance allele frequency.
- Disruptive (diversifying) selection favors both extremes and can create bimodality; pesticide exposure favors only the resistant extreme, not both extremes.
- Heterozygote advantage means heterozygotes have higher fitness than either homozygote (e.g., sickle-cell resistance to malaria); pesticide resistance is typically advantageous in any genotype carrying resistance alleles, not specifically heterozygotes.

Conclusion: This example is directional selection, matching the provided answer "directional selection."

The rapid development of resistance to pesticides such as DDT in insect populations is an example of: 单项选择题

类似问题

Like natural selection, adaptation is a haphazard process because:

What interaction is most important in natural selection?

Which statement is NOT one of Charles Darwin's proposed criteria for traits to evolve through natural selection?

Which of the following observations is the best example of evolution at work?

Who was the famous scientist that based a lot of his pivotal conclusions on his observations of orchids

Charles Darwin acknowledged the importance of sexual reproduction when formulating his theory of natural selection.

Charles Darwin recognized the importance of beak variation in finches while visiting the Galápagos Islands.

In formulating his theory of natural selection, Darwin appreciated the fact that population size is limited by availability of food.

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单