Chapter 18 - Populations and Evolution Flashcards
What is a gene pool
All the alleles for a particular gene in the breeding individuals at a particular time
What is the allele frequency?
the number of times an allele occurs in a gene pool, compared to the total number of alleles in that pool for the same gene
What is the Hardy-Weinberg Principle?
What assumptions do Hardy-Weinberg work off?
Random mating
No mutations
No immigration or emigration
All genotypes are fertile
Large population
What genetic factors lead to variation?
Mutations
Meiosis- independent segregation and crossing over
Random fertilisation of gametes
How does evolution by natural selection lead to an increase in allelic frequencies?
There area variety of phenotypes in a population
A change in the environment causes a change/ introduction of a new selection pressure
Individuals that possess advantageous alleles have a selective advantage so will survive and reproduce
These advantageous alleles are passed to their offspring and overtime the frequency of the allele will increase
What is stabilising selection?
In stabilising selection, an average phenotype is selected for and extreme phenotypes are selected against
What is directional selection?
Type of selection where one extreme phenotype is selection for and means that over time the mean will shift in that direction due to selection pressure
What is disruptive selection?
Type of selection where the extreme phenotypes are selected for and the intermediate phenotypes are selected against
How does allopatric speciation work?
Geographical isolation of species which mean there is no interbreeding
Selection pressure such as changing environment causes mutations to occur in line with advantageous alleles (directional selection)
No gene flow between different gene pools
Change in frequency of alleles
Eventually different species cannot breed to produce fertile offspring
How does sympatric speciation work?
Organisms in the same area become reproductively isolated and mutations occur
Leads to a change in allele frequency due to disruptive selection
This means over a long period of time, different species cannot interbreed to produce fertile offspring
What is genetic drift?
Change in allele frequency within a population between generations
Why is genetic drift only important is small populations?
Smaller genetic diversity
Those alleles that are passed on will affect the whole population
Allele frequency will be high
Mutations that lead to selectively favoured alleles will affect the whole population
High allele frequency
