Lecture 10-11 - Evolution of Resistance

Question 1

Define polygenic inheritance.

Answer 1

Many genes combine to determine a characteristics

Question 2

Explain how resistance to pesticides increases over time.

Answer 2

Let’s take the example in mosquitos. Initially, resistance genes are rare before pesticide is used. Chance of reproduction and passing of resistance within the mosquito population is small. However, with pesticide application, as time goes by, pesticide gets diluted over time. After a while, dose may be low enough for some resistant mosquitos to survive while killing the rest. This increases the rate at which the resistant gene is transmitted within the population (selection).

Question 3

Explain the concept of selection time and zone of selection.

Answer 3

Selection time refers to the time frame in which the dosage is low enough to kill the wild type but not the mutated ones. Zone of selection refers to the dosage level differences acceptable between wild-type and mutated.

Question 4

Mention measures to minimise selection for resistance

Answer 4

• Repeat regularly to keep high dosage
• Use chemical with rapid decay (minimise selection time)
• Prevent unnecessary usage
• minimise edge effects for pesticides

Question 5

Explain how the concept of mutation in pests may not always result in favorable traits. Why then are some mutated traits stay prevalent in the population? What is this phenomenon called?

Answer 5

New mutations always have a bad side effect (including pesticide resistance mutation). Therefore, without the proper environmental pressure, the mutation will be selected against. However, if enough biological pressure is continuously applied (continued use of weak pesticide), the benefits of the mutation may outweigh the side effects. This is referred to stabilization of resistance.

Question 6

Define symbionts

Answer 6

Symbionts: organism living together

Question 7

Explain the Host-Parasite evolution concept.

Answer 7

Under normal condition, virulence of parasites are reduced. This is the case as the host would have a weaker response to the parasite.

Hosts also evolve to be more resistant, as resistant hosts reproduce more.

Question 8

Differ between horizontal and vertical transmission of disease.

Answer 8

Horizontal transmission: between individuals, or via vector or intermediate host

vertical transmission: inter-generational

Question 9

No. of infected individuals is proportional to three factors. Mention them.

Answer 9

Probability of passing disease, effective number of contacts, duration of infectiousness