B18 - Population genetics Flashcards
What is population genetics?
The study of genes and alleles of an entire population, not just how it is passed on from one individual to another
What is a gene pool?
All the alleles of all the genes of all the individuals in a population at a given time
What is allele frequency?
The number of times an allele occurs within the gene pool
What are the 2 Hardy-Weinberg equations?
P + Q = 1 - determines the allele frequency
P² + 2PQ + Q² = 1 - determines the genotype frequency
What are 3 causes of genetic variation?
Mutations
Meiosis
Random fertilisation of gametes
What is stabilising selection?
Preserves average phenotype
Eliminates extreme phenotypes therefore usually occurs when environmental conditions have been constant for a long period of time
What is directional selection?
Favouring one phenotype in one direction from average
If environmental conditions change, so will the optimum value of phenotype for survival. Some individuals on the left or right will have a combination of alleles with the new optimum for the new conditions
What is disruptive selection?
Favours individuals with extreme phenotypes
It arises when an environmental factor take two or more distinct forms.
With the fur example, if temperatures alternated between 5oC in winter and 15oC in summer, ultimately two separate species of the mammal could occur, one which active in the winter and one which active in the summer
What does having a phenotype with selective advantage allow?
Phenotypes with selective advantage will allow organisms to survive, produce offspring and pass on the favourable alleles
What is speciation?
Evolution of a new species from existing ones
What is a species?
A group of individuals that have common ancestry and so share the same genes but different alleles and are capable of breeding with one another to produce fertile offspring
What is allopatric speciation?
Due to geographical separation, like a physical barrier which separates populations and potentially have different environmental effects on either side. Therefore no gene flow between populations
Different environments → different selection pressures
Different mutations result in different beneficial alleles
Allele frequency changes
Accumulation of differences in the two gene pools prevent interbreeding
What is sympatric speciation?
Speciation within a population in the same area, due to new or shared resources
Speciation happens in time. Different breeding seasons
Different mutations
Allele frequency changes
Accumulation of differences in the two gene pools prevent interbreeding
What is genetic drift?
Occurs in small populations. Some individuals (with their alleles) are randomly removed from the original population (random event). This results in a reduction in genetic variation as there is a smaller variety of alleles. Those that get passed on will affect the whole population quickly and their frequency will be high. Can result in separate species
