Inheritance, Variation & Evolution

12 methods · 27 questions

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Selection acts only on variation already present in a population, and that variation comes from random mutation, never from the environment or the selection pressure that later favours it. Any statement that a pressure or an environmental change CAUSED or DIRECTED a mutation is wrong, and any statement that a population had NO variation is wrong.

Trigger: a multi-statement question about evolution, resistance or adaptation where one option makes the environment the source of the useful variant.

Instances:
(i) a claim that a selection pressure (pesticide, antibiotic, drought, food type) caused the advantageous mutations to appear is false, mutations arise at random and the pressure only selects among them;
(ii) a claim that the losing group showed no genetic variation is false, every population varies, the group simply lacked the variant that helped;
(iii) natural selection needs variation to act on, so maintaining variation (for example untreated refugia) slows adaptation, and multiple alleles being present is what makes selection possible;
(iv) a selection pressure is anything that changes who survives and reproduces (habitat loss, a new predator, an antibiotic, an insecticide all qualify).

Linked questions (3)

NSAA 2016 Section 1, Part D (Biology questions) · Q55

Between 1954 and 1971 a mine in Northern Australia was releasing excess copper into the nearby Finnis River. Copper ions are poisonous and most of the types of fish living in the river died. The river still remains polluted with copper, but scientists have discovered one type of rainbow fish that is able to survive and live in the river.

A student wrote the following statements in order to explain this information.

1. One type of rainbow fish did not die out in the river because this type was able to adapt to the changing environment.
2. None of the other types of fish showed any type of genetic variation.
3. The presence of copper ions acted as a selective pressure.

Which of the student's statements could be correct?

A1 only
B1 and 2 only
C1 and 3 only
D2 and 3 only
E1, 2 and 3

Worked solution

Answer:C

Statement 3 is correct: the copper ions killed most of the fish, so they acted as a selective pressure favouring any individuals that could tolerate copper.

Statement 2 cannot be correct. Every population shows some genetic variation; the other types of fish died out because none of their variants happened to give copper tolerance, not because variation was absent.

Statement 1 could be correct when "this type" is read as the population: a variety of rainbow fish that already contained tolerance alleles survived and reproduced, so the type as a whole became adapted to the new conditions. Since no option offers statement 3 on its own, the only consistent choice is 1 and 3.

The answer is C.

NSAA 2018 Section 1, Part D (Biology questions) · Q71

Bt pesticide is used by farmers to kill insect pests. However, widespread use has resulted in the evolution of resistance to this pesticide. A recessive allele causes resistance.

Scientists have suggested that in areas where the Bt pesticide is used, a small number of fields are left untreated. These untreated fields are known as refugia. This method has been shown to slow down evolution of resistance to the pesticide.

Which of the following statements explain why refugia could slow down the evolution of resistance to Bt pesticide?

1. When resistant insects breed with pesticide-sensitive insects that do not have the allele for resistance, the offspring produced will be sensitive to the pesticide.
2. When fewer insects are exposed to pesticide, fewer mutations occur that produce alleles for resistance.
3. The refugia help to maintain genetic variation in the population of insect pests.

Anone of them
B1 only
C2 only
D3 only
E1 and 2 only
F1 and 3 only
G2 and 3 only
H1, 2 and 3

Worked solution

Answer:F

Resistance is recessive, so a resistant insect (rr) that mates with a sensitive insect carrying no resistance allele (RR) produces heterozygous offspring (Rr), which are sensitive to the pesticide. The untreated refugia keep plenty of sensitive insects alive to breed with any resistant survivors, so statement 1 explains the effect.

Statement 2 is wrong: the pesticide does not cause the resistance mutations, it only selects the resistant insects that arise anyway, so exposing fewer insects does not reduce the number of mutations.

Statement 3 is correct: the refugia preserve the sensitive alleles and so maintain genetic variation in the pest population, instead of letting the resistant allele take over.

The answer is F.

NSAA 2020 Section 1, Part D (Biology questions) · Q69

The table shows information about a human genetic condition called sickle cell anaemia and an infection called malaria. Both sickle cell anaemia and malaria can be fatal.

genotype MM Mm mm phenotype does not show sickle cell anaemia does not show sickle cell anaemia shows sickle cell anaemia comment can be infected with malaria shows resistance to malaria shows more resistance to malaria than Mm

Which of the following statements is/are correct?

1. In areas without malaria, human populations are likely to have a low number of people with the m allele.
2. In areas with malaria, only those individuals that are heterozygous will be able to pass on their alleles to the next generation.
3. Presence of malaria has caused a mutation of the M allele to the m allele leading to an increased chance of survival in the heterozygous state.

Anone of them
B1 only
C2 only
D3 only
E1 and 2 only
F1 and 3 only
G2 and 3 only
H1, 2 and 3

Worked solution

Answer:B

Where there is no malaria the m allele brings no advantage and mm can be fatal, so natural selection keeps the allele rare (1).

Statement 2 is wrong: MM people can survive malaria and breed, and so can some mm people, even if fewer of them do. Heterozygotes are favoured, but they are not the only ones that reproduce.

Statement 3 is wrong: mutations arise at random and are not caused by malaria. Malaria only selects for the heterozygotes among the variants already present in the population.

The answer is B.