Population Genetics

Question 1

List the factors that can alter the Hardy-Weinberg equilibrium

Answer 1

1. Genetic drift and bottlenecks
2. Migration
3. Positive assortment mating
4. Negative assortment mating
5. Mutation
6. Natural selection

Question 2

How do you calculate sampling variance?

Answer 2

pq/N(population size)

Question 3

What is genetic drift?

Answer 3

Variation in allele frequencies due to chance disappearance of particular alleles

More of an effect in small populations

Question 4

What is a population bottleneck?

Answer 4

Sharp reduction in population due to environmental events

Question 5

Give an example of a population bottleneck

Answer 5

Cheetahs experienced a population bottleneck around 10,000 years ago.
As a result have very low levels of genetic variation

European bison- went through bottleneck in early 20th century. All today are descendants of 12 individuals, and have subsequently very low genetic diversity
(Luenser et al., 2005)

Question 6

Give examples of genetic drift

Answer 6

Drosophila
• Maintain 2 populations of red and white eyed drosophila in a cage and measure phenotype frequency. Eventually one colour goes extinct

In small populations more likely:
Isolated populations like Finland
• Set of 33 damaging recessive alleles found nowhere else in the world (inbreeding)

Question 7

Define inbreeding depression

Answer 7

Reduced biological fitness as a result of inbreeding

Question 8

Give an example of migration affecting HW

Answer 8

Admixture between human populations of African and European origin

Admixture between Cuban brown anole and native lizards when introduced into areas such as Florida- freely interbred

Question 9

Give examples of positive assortment mating

Answer 9

Humans- dependant on factors such as race, religion, education, collar size

Animals- mating more likely between individuals of similar size and colour.

Question 10

Give examples of negative assortment mating

Answer 10

Plants- self-incompatibility alleles act as outbreeding mechanism

Wolves in Yellowstone- grey with black
(Hendrick et al., 2016)

BRUCE effect in mice- terminate pregnancy when exposed to scent of unfamiliar male

Humans- Tay Sachs in Ashkenazi Jews, testing people for heterozygosity and match-making

Question 11

Explain how mutation affects HW and give examples

Answer 11

Allele frequencies will change if new alleles emerge in a population

Cytochrome C mutations often have no effect on fitness so accumulate in populations. Allele frequencies therefore give information on when species diverged from each other

Question 12

Give examples of how natural selection affects HW

Answer 12

Peppered moth
• Black appeared ~1848
• Industrial revolution- black advantage in in polluted areas- incidence of phenotype much higher
• Reduced after pollution reduced

Pesticide resistance in insects and weeds
• rodent poison resistance acquired by house mice from Algerian mice through introgressive hybridisation
(Song et al., 2011)

Humans
• Geographical skin colour variation

Antimicrobial resistance:
Selective pressure results in rapid adaption of resistance
• Antibiotic- MRSA- Methicillin-resistant bacteria
• Antiviral-resistant influenza strains develop

• Flu virus can develop resistance to human antibodies as a result of antigenic drift (mutations within antibody coding genes) and selection pressure. Also from antigenic shift- combined genes from different strains of viruses