Population Genetics Flashcards
Give the 4 characteristics of an Ideal Population
- All genes are equally likely to copy themselves
- No mutations
- No immigration or migration
- Random mating
What is the Hardy Weinberg Equilibrium?
p^2 = frequency of AA
q^2 = frequency of aa
2pq = frequency Aa
p + q = 1
Give an example of how carrier frequency is greater that sufferer frequency
Cystic fibrosis- 1 in 25 ar Ff and only 1 in 2500 have ff
Name the 5 ways in which the H-W equilibrium can be altered
- Bottlenecks in the Population
- Genetic Drift
- Inbreeding
- Selection
- Mutation
- Migration
What is meant by Genetic Drift?
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
What decreases the effect of Genetic drift?
A large population.
What is the formula for Shift in allele frequency?
=(pq/N)^1/2
N= is the average no. of parents per generation
p and q are allele frequencies
Define the term Bottleneck
When a population’s size is reduced for at least one generation.
What effect does Bottleneck have on GD ?
It can increase GD and decrease genetic variation as a consequence. Any past bottleneck decreases N
What is the formula to calculate the Harmonic Mean (of N)
= K ÷ (1/N1 + 1/N2 + 1/N3 + … + 1/NK)
K = number of generation Nk = number of parents in that generation.
Give an example of how Bottlenecks can reduce genetic diversity.
Tristan Da Cunha and Retinoblastoma- Island populated by 5 founders and grew. Bottlenecks: fishing accidents, mass emigration, volcanic eruption- Consequently lots of inbreeding
Explain what is meant by the Founder Effect.
A reduction in genetic diversity which results when a population is descended from a small number of colonizing ancestors
Explain how the Island Tristan Da Cunha is an example of the Founder effect
Only 5 founders- increased incidence of Retinoblastoma (eye cancer) due to homozygosity by descent.
Give another example of the Founder effect
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.
Explain how Migration can affect the H-W equilibrium.
Populations admix (new alleles introduced) this interferes with native allele frequencies.
Give an example of how Migration has affected allele frequencies.
Skin colour in the UK - introduction of darker skin allele due to immigration.
Define Assortative Mating and how does this affect the H-W equilibrium?
Selective Mating (non Random). Some alleles (phenotypes) may be preferentially selected by mates
Give an example of Positive Assortative Mating
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.
Give an example of Assortative Mating in Humans
Levels of Education- a graduate is 5x more likely to marry another graduate than someone who has no GCSE’s
Give an example of Negative assortative mating
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.
What is the Bruce Effect? What is this an example of?
In mice, aka pregnancy block. Pregnant females will terminate preg if exposed to urine of non-self line males.
What are the mechanisms behind the Bruce Effect?
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.
How can Natural Selection affect the H-W equilibrium?
NS is the inherited difference in ability to survive and reproduce - not all genotypes have equal chance
Define the Selective value given to genotypes
The value is a measure of a genotypes ability to contribute to the next generation.
When aa is lethal, what are the relative allele frequencies after selection?
AA = p/1+q Aa = 2q/1+q
Give an example of Natural Selection
Antibiotic resistance- clear correlation between high antibiotic use and resistant bacteria.
How is antibiotic resistance passed on?
Horizontal gene transfer- plasmids containing resistance are copied and passed on to daughter cell. An example is MRSA.
