Population Genetics

Question 1

Give the 4 characteristics of an Ideal Population

Answer 1

• All genes are equally likely to copy themselves
• No mutations
• No immigration or migration
• Random mating

Question 2

What is the Hardy Weinberg Equilibrium?

Answer 2

p^2 = frequency of AA
q^2 = frequency of aa
2pq = frequency Aa
p + q = 1

Question 3

Give an example of how carrier frequency is greater that sufferer frequency

Answer 3

Cystic fibrosis- 1 in 25 ar Ff and only 1 in 2500 have ff

Question 4

Name the 5 ways in which the H-W equilibrium can be altered

Answer 4

• Bottlenecks in the Population
• Genetic Drift
• Inbreeding
• Selection
• Mutation
• Migration

Question 5

What is meant by Genetic Drift?

Answer 5

The random changes in gene frequency through accidents of sampling- the variation of allele frequencies due to disappearance of particular genes as individuals fail to reproduce. Drift is caused by large Shifts in allele frequency

Question 6

What decreases the effect of Genetic drift?

Answer 6

A large population.

Question 7

What is the formula for Shift in allele frequency?

Answer 7

=(pq/N)^1/2

N= is the average no. of parents per generation
p and q are allele frequencies

Question 8

Define the term Bottleneck

Answer 8

When a population’s size is reduced for at least one generation.

Question 9

What effect does Bottleneck have on GD ?

Answer 9

It can increase GD and decrease genetic variation as a consequence. Any past bottleneck decreases N

Question 10

What is the formula to calculate the Harmonic Mean (of N)

Answer 10

= K ÷ (1/N1 + 1/N2 + 1/N3 + … + 1/NK)

K = number of generation
Nk = number of parents in that generation.

Question 11

Give an example of how Bottlenecks can reduce genetic diversity.

Answer 11

Tristan Da Cunha and Retinoblastoma- Island populated by 5 founders and grew. Bottlenecks: fishing accidents, mass emigration, volcanic eruption- Consequently lots of inbreeding

Question 12

Explain what is meant by the Founder Effect.

Answer 12

A reduction in genetic diversity which results when a population is descended from a small number of colonizing ancestors

Question 13

Explain how the Island Tristan Da Cunha is an example of the Founder effect

Answer 13

Only 5 founders- increased incidence of Retinoblastoma (eye cancer) due to homozygosity by descent.

Question 14

Give another example of the Founder effect

Answer 14

The Amish Community of North America. Colonial ancestors originated from Europe. Have the highest incidence of a rare Ellis-van-Creveld syndrome which can be traced back to one person.

Question 15

Explain how Migration can affect the H-W equilibrium.

Answer 15

Populations admix (new alleles introduced) this interferes with native allele frequencies.

Question 16

Give an example of how Migration has affected allele frequencies.

Answer 16

Skin colour in the UK - introduction of darker skin allele due to immigration.

Question 17

Define Assortative Mating and how does this affect the H-W equilibrium?

Answer 17

Selective Mating (non Random). Some alleles (phenotypes) may be preferentially selected by mates

Question 18

Give an example of Positive Assortative Mating

Answer 18

Rhagoletis Pomonella- a fly that inhabits hawthorn and now apples. Apple inhabiting flies prefer to mate with each other same with hawthorn flies despite both being of the same species.

Question 19

Give an example of Assortative Mating in Humans

Answer 19

Levels of Education- a graduate is 5x more likely to marry another graduate than someone who has no GCSE’s

Question 20

Give an example of Negative assortative mating

Answer 20

Hermaphrodite Plants- are self sterile enforced by Self incompatibility alleles, if pollen (n) and style (2n) share one allele in common, no pollen tube made, no fertilisation.

Question 21

What is the Bruce Effect? What is this an example of?

Answer 21

In mice, aka pregnancy block. Pregnant females will terminate preg if exposed to urine of non-self line males.

Question 22

What are the mechanisms behind the Bruce Effect?

Answer 22

The Vomeronasal organ in the nose of mouse can detect MHC 1 types (secreted in urine) females can detect non-self MHC1 and will preferentially want to mate.

Question 23

How can Natural Selection affect the H-W equilibrium?

Answer 23

NS is the inherited difference in ability to survive and reproduce - not all genotypes have equal chance

Question 24

Define the Selective value given to genotypes

Answer 24

The value is a measure of a genotypes ability to contribute to the next generation.

Question 25

When aa is lethal, what are the relative allele frequencies after selection?

Answer 25

AA = p/1+q
Aa = 2q/1+q

Question 26

Give an example of Natural Selection

Answer 26

Antibiotic resistance- clear correlation between high antibiotic use and resistant bacteria.

Question 27

How is antibiotic resistance passed on?

Answer 27

Horizontal gene transfer- plasmids containing resistance are copied and passed on to daughter cell. An example is MRSA.