B18- Population and Evolution Flashcards
What is population genetics?
Population genetics studies genes and alleles of an entire population, not just how it is passed on from one individual to another.
What is a population?
Population - a group of organisms of the same species that occupy a particular space at a particular time and can potentially interbreed.
What is a gene pool?
Gene pool - all the alleles of all the genes of all the individuals in a population at a given time.
What is allele frequency?
Allele frequency - the number of times an allele occurs within the gene pool
What is a species?
Can interbreed to produce fertile offspring
How can variation occur in phenotypes?
Factors Contributing to Allelic Variation in a Species:
- Random fertilisation: Gametes with different alleles combine randomly
- Meiosis: Random assortment of alleles during gamete formation
- Mutation: Creation of new alleles that can be inherited
- Environmental influences: Impact on phenotypic expression of traits
What is the Harvey-Weinberg principle?
Used to calculate allele frequencies in a particular population
p^2 + 2pq+ q^2=1
p+q=1
What is natural selection?
Process of evolution by natural selection depends on a number of factors:
More offspring is produced than can be supported by resources
Genetic variety in population
Variety of phenotypes that selection operates against
What are selection pressures and what do they determine?
Selection pressures - environmental factors that limit a population
These vary from time to time and place to place.
Selection pressures determine allele frequency within a gene pool (total number of all alleles of all genes of all individuals at a given time).
Why do some species have high reproduction rates?
To ensure that population survives to breed and reproduce the next generation
The more intraspecific competition the more struggle to survive therefore survival based on favourable allele combination. Therefore allele frequency will change.
What is the role of variation in natural selection?
Sexual reproduction means more offspring might be less likely to survive. However the larger the genetic variation in a population, the more likely that some individuals will have favourable allele combinations to adapt and survive.
How does stabilising selection help survival?
Eliminates extreme phenotypes therefore usually occurs when environmental condition have been kept at a constant for a long period of time.
What is directional selection and how does it help survival?
If environment condition change, so optimum phenotype will survive however some individuals on both sides will have allele that are optimum for the new conditions.
How does disruptive selection help survival?
Brings evolutionary change as it arises when environmental factor take two distinctive forms such as 5 degree in winter and 15 degrees in summer ultimately two species are formed.
What is the peppered moth an example of?
Selective predation - predator favours the individual at one extreme, or another one of a range of phenotypes
Directional selection resulting in black populations in industrialised areas and white populations in rural areas.
How is allele frequency affected by selection?
Due to environmental changes affecting the probability certain alleles are able to be passed on and therefore allele frequency in the gene pool.
What is speciation?
Speciation is the process by which new species evolve from existing ones
What is allopatric speciation?
Due to geographical separation, like a physical barrier which separates populations and potentially have different environmental effects on either side.
Different environments -> different selection pressures
Different mutations result in different beneficial alleles
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.
What is adaptive radiation?
Is a process in which organism diversify from a common ancestors in response to environmental change however due to allelic frequencies changing will no longer be able to interbreed and and a new species is formed with its own gene pool.
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.
