Lecture 8: Variation, selection and adaption

Question 1

Classic example of natural selection (moth) INFO

Answer 1

Peppered moth (Biston betularia)
Two morphs:
1) Typical (typical) form
2) Melanic (carbonara) form
GENETICS: -controlled by a single gene with 2 alleles.
-Melanic allele (M) is dominant to the typical allele (+)

Question 2

Classic example of natural selection (moth) HISTORY

Answer 2

The melanic form was first seen in Manchester in 1848
-its frequency increased 1-10% in industrial areas by 1898
-had a freq of >99% in Manchester in 1948.
Typical form remained common in rural areas

Question 3

Typical form:

Answer 3

grey/ lighter form

Question 4

Melanic form:

Answer 4

Black form

Question 5

The relative fitness of different genotypes is calculated by..

Answer 5

taking the most favoured genotype as the standard with a fitness of 1.0 from % recaptured

Question 6

The selection coefficient (s) against a disfavoured genotype is calculated by

Answer 6

difference between the fitness of the standard (taken as 1.0) & the relative fitness of the genotype in question.

Question 7

The increase in frequency of the melanic form in polluted areas was driven by

Answer 7

POSTIVE SELECTION

Question 8

After the clean air act-

Answer 8

1959 onwards.

As pollution declines the melanic form is no longer cryptic to birds and so it loses its fitness advantage.

Question 9

Adapted melanism in rock-pocket mice (Chaetodipus intermedius)

Answer 9

-coat colour determined by the melanocortin 1 receptor gene (MC1R).
D (dark) is dominant to d (light)

Question 10

Rock-pocket mice two different environments..

Answer 10

• light-coloured sandy substrate in most of its range. Mice generally have lighter hair.
• In area with a lot of BASALT (black rock from volcano), the dark form i common.

Question 11

Rock-pocket mice predators

Answer 11

owls and mammalian carnivores

Question 12

HIV..

Answer 12

human immunodeficiency virus

Question 13

HIV and AIDS

Answer 13

HIV is the pathogen causing aids (acquired immunodeficiency syndrome), with almost 100% fatality

Question 14

When was AIDS first recognised & how many

Answer 14

in 1981; 42 million people infected worldwide, 5 million new infections per year

Question 15

AID is a single/ double strand of DNA/RNA virus??

Answer 15

single stranded RNA virus

Question 16

HIV makes an enzyme called..

Answer 16

reverse transcriptase (RT). RT converts RNA into double-stranded DNA; key step in the life cycle of HIV; prerequisite for replication

Question 17

Whats 3TC and what does it do?

Answer 17

HIV drug.
It interferes with the normal RT, blocking the reproduction of HIV. HIV strains with mutant RTs that differ from the normal RT at the 184th a.a. are resistant to 3TC. The mutants have functional defects (rare in the absence of 3TC)
In 4 Weeks host becomes resistant, drug no longer effective.

Question 18

Whats helping HIV to evade the drug 3TC?

Answer 18

• reverse transcriptase is error prone (HIV has a very high mutation rate [~3.4 X10^-5/site/generation])
• Generation time of 2.5 days
• An extremely large population size

Question 19

HIV lifecycle and recombination

Answer 19

Recombination is an integral part of the HIV lifecycle, occurring when reverse transcriptase switches between alternative genomic templates during replication

Question 20

Examples of positive selection

Answer 20

• peppered moth, rock-pocket mice, HIV
• evidence from genotypes and phenotypes
• positive selection can drive advantageous phenotypes and genotypes to high frequencies

Question 21

Positive selection is just one example of

Answer 21

natural selection

Question 22

Sickle-cell anaemia

Answer 22

• a recessive disorder caused by a mutation in the beta-haemoglobin gene; 80% die before reproduction
• S (disease form) is recessive to A (normal form)
• AA: no anaemia
• AS: usually healthy some with mild anaemia
• SS: severe anaemia

Question 23

link between anaemia and malaria

Answer 23

Anaemia kills the malaria.
AA: susceptible to severe malaria
AS: quite resistant
SS: mostly killed by anaemia

Question 24

AS red blood cells and sickling

Answer 24

Do not normally sickle. They do when they become infected with Plasmodium falciparum (causes malaria). The cell is destroyed and the parasite killed in the process.

Question 25

The S allele (for anaemia) is maintained at..

Answer 25

high frequencies by natural selection

Question 26

Balancing selection..

Answer 26

another form of natural selection; it can happen when heterozygotes are fitter than homozygotes. (such as S allele in africa malaria infested parts)

Question 27

Kuru and the PRNP gene

Answer 27

cannibalism banned in the 1950s.

Heterozygotes have highest fitness. PRNP was under balancing selection when kuru was present.

Question 28

Kuru:

Answer 28

a prion disease similar to mad cow disease and Variant CJD (vCJD); no cure, fatal. Spread by consumption of prion infected meat. When men die women and children consume flesh in cannibalistic rituals. Genetic variation at the prion protein gene (PRNP) is associated with susceptibility to prion disease in various species.

Question 29

Two forms of natural selection

Answer 29

1) positive selection e.g drug resistance

2) Balancing selection e.g. Kuru