Speciation Flashcards
What genetic factors cause variations in phenotype?
- mutations
- meiosis
- random fertilisation of gametes
How do these genetic factors cause genetic variation?
- mutations are the primary source of variation and causes new alleles to arise, increasing the size of the gene pool
- meiosis produces new combinations of alleles through crossing over and independent segregation
- random fertilisation means that gametes fuse randomly, further creating new genetic differences for offspring
How do environmental factors cause genetic variation?
- the environment has a large influence on how an organisms genes are expressed and affects the phenotype of an individual
- this includes climate, temperature, PH and food avaliability
What three factors cause an organism to be subjected to selection pressures?
- predation
- disease
- competition
What do selection pressures determine?
- the frequency of alleles in a gene pool
What do selection pressures cause?
- natural selection
- this means that there are differential reproductive successes on allele frequencys
Why do organisms over reproduce?
- to ensure a sufficient population survives and can reproduce, producing the next generation
- However, this can cause intraspecific competition to occur as there is a high population for a limited amount of resources
- also in larger populations, there is more genetic variation, increasing the chances of an individual developing a beneficial allele
What is the effect of stabilising selection?
- the extremes of a phenotype are eliminated, leaving the average phenotype
- however, when environmental conditions fluctuate, extremes can be favoured
What is the effect of directional selection?
- extreme phenotypes are favoured and normal distribution will move in one direction due to fluctuating environmental conditions
What is disruptive selection?
- the opposite of stabilising selection
- this occurs when an environmental change exists in two distinct forms, favouring the two extremes
Define evolution
the change in allelic frequencies within a population
Define speciation
The reproductive isolation leading to the evolution of a new species from existing ones
How does speciation occur?
- reproductive seperation
- this occurs when there is a change in alleles and phenotypes of some individuals in a population which prevents successful breeding with other individuals in a population
What changes can cause reproductive seperation?
- seasonal changes
- mechanical changes
- behavioural changes
What does reproductive isolation mean?
- two populations of a species no longer interbreed and can not produce fertile offspring
What are the two types of speciation?
- Allopatric speciation
- Sympatric speciation
What occurs during allopatric speciation?
- two populations are geographically seperated due to geographical barriers such as lakes and oceans
- this means they are reproductively seperated and if there are environmental differences, they face different selection pressures
- this means natural selection pressures will occur and each population will evolve differently
- this eventually leads to two different species forming
What occurs during sympatric speciation?
- this takes place when there are no geographic barriers and two populations are split due to ecological or behavioural changes
Give an example of sympatric speciation
- two populations of fish feed in different places
- one population feeds in open water whereas the other feeds in deep waters
- this ecologically seperates the populations
- there are different selection pressures in the different environments
- for example, longer jaws may be more suitable for deeper waters, this causes natural selection to occur
- this means over time they will continue to diverge until they become different species
What is genetic drift?
- when chance affects which individuals in a population survive, breed and pass on their alleles
What type of population does genetic drift affect?
- it affects smaller populations
Why does genetic drift only affect smaller populations?
- In smaller populations, there is a small gene pool and little genetic variation
- this means that there is not an even chance for alleles to be passed on
- alleles that are passed on affect the whole population, causing genetic drift
- in large populations, genetic drift is limited as alleles are diluted in a large population
