Population genetics Flashcards
What is the gene pool?
the total information from all the genes and alleles of breeding individuals in a population at a particular time
What is the allele frequency?
the proportion of organisms in the population carrying a particular allele
What does it mean about the population if there is a change in allele frequency?
the population is evolving
In larger populations, allele frequencies remain…
generally stable
What are the two equations for the Hardy-Weinberg principle?
p + q = 1
p^2 + 2pq + q^2 = 1
What does this equation relate to p + q = 1?
alleles of one gene, p = dominant allele frequency, q = recessive allele frequency
What does this equation relate to p^2 + 2pq + q^2 = 1?
individuals in a population, p^2 = frequency of homozygous dominant, 2pq = frequency of heterozygous, q^2 = frequency of homozygous recessive
What does the Hardy-Weinberg principle assume?
that the population is:
-large
-has random mating
-is experiencing no selection
-has no mutation or migration
What is disruptive selection?
selection pressure towards the extremes that creates two modal values
What does disruptive selection cause?
sympatric speciation
What are forces of evolutionary change?
natural selection, genetic drift
What is genetic drift?
a change in allele frequency due to chance rather than selection
What does genetic drift have a bigger impact on?
smaller populations
Use the example of a bird and green/brown bugs to explain the difference between natural selection and genetic drift
-natural selection - a bird is more likely to see the green bug over a brown one
-genetic drift - a random green beetle is stood on
When does natural selection occur?
when alleles that enhance the fitness of the individuals that carry them rise in frequency
What can cause genetic variation?
-mutation
-independent segregation
-crossing over
-random fertilisation of gametes
What causes interspecific variation?
-differences in DNA
-structure and sequence of genes
-the way in which genes are expressed
What can cause intraspecific variation?
a combination of both environmental and genetic factors, and epigenetics
What are the two types of variation?
discontinuous and continuous
What is discontinuous variation?
limited to a fixed number of traits, such as blood group - a few genes with multiple alleles. the environment usually has a lesser effect
What is continuous variation?
controlled by many genes, environment has a significant effect, and is more likely to be a number like weight
How can we make a sample more representative?
-increase study size
-reduce sampling bias by random sampling
What can be used to determine the relative importance of the environment and genes?
twin studies - identical vs non-identical
What happens if a species becomes isolated from the other populations?
-there will be no gene flow between the isolated population and the others
-this may lead to the accumulation of genetic differences
-leading to the isolated population being unable to breed and produce fertile offspring with organisms from the other population
-this reproductive isolation means that a new species has evolved
What is speciation?
an evolutionary process that results in the formation of a new species from a pre-existing species
What are the two ways in which speciation can occur?
allopatric and sympatric
What is isolation?
when two populations are separated, leading to no gene flow
What is allopatric speciation?
-occurs when a geographical barrier physically isolates populations of a species
-the two populations begin to evolve separately as a result of a random mutation, genetic drift, and natural selection
-eventually the two populations reach a degree of genetic difference where they can no longer interbreed to produce fertile offspring
What is sympatric speciation?
-divergence of species within the same geographical location
-may be due to genetic abnormalities/differences
-prevents interbreeding between those species to produce fertile offspring
