pack 20 natural selection Flashcards
(21 cards)
what does natural selection cause
natural selection is the process that leads to evolution
what does evolution mean
evolution is the change in the frequency of alleles within a population over many generations
name the 3 cause of genetic variation
-mutations
- meiosis
- random fussion of gametes
what causes selection pressures and how
predation, disease, competition and changes in the environment result in selection pressures giving some phenotypes a selective advantage acting as a trigger for natural selection to occur.
describe the process of natural selection
- there is a variation in a population
- this is due to a mutation, giving rise to new alleles of a gene
- organisms with the advantageous allele, will have a phenotype that gives them a selective advantage in their environment
- organisms with the advantageous alleles are more likely to survive to reproduce or at least have more offspring than others
- these organisms are therefore more likely to pass on their advantageous alleles to the next generation than the others
- this causes an increase in the frequency of the advantageous allele in the population over many generations
name the 3 different adaptations and description
-anatomical- changes to the organisms body
- physiological- haemoglobin with different oxygen affinity
- behavioural - better food search strategies
name the 3 types of natural selections
- directional
- stabilising
- disruptive
what is directional selection
- directional selection acts against one of the extreme phenotypes and selects the other
-results in an increase in the frequency of alleles
what is stabilising selection
- acts against both the extremes in a range of phenotypes i.e favours the middle phenotypes and so acts to prevent change
what is disruptive selection
- individuals with both extremes of a phenotype have a selective advantage over those in the middle so both are selected
what does species mean
a group of organisms with similar characteristics that can interbreed to produce fertile offspring
what does speciation mean
speciation is a process whereby one gene pool gives rise to more than one gene pool.
what are the two types of speciation
- allopatric
- sympatric
where does this occur - allopatric
when two populations of the same species becomes geographically separated by a physical barrier
what is allopatric speciation
- parts of population becomes geographically isolated
- no interbreeding occurs between the populations
- different environments lead to different selection pressures
- different beneficial mutations may occur leading to formation of different advantageous alleles
- in each population organisms with the advantageous phenotype will be more likely to survive an reproduce than those without, and so the allele frequencies in each population will cahnge over many generations
eventually the genotype of the two populations may become so different that, even if members of each grop were reunited, they would no longer successfully interbreed to produce fertile offsprings - the two populations are now classified as different species
what is reproductive isolation
a set of barriers that exist between different species that make them unable to breed and produce healthy offspring - in sympatric speciation it is the presence of a random mutation
what are the causes of sympatric speciation
seasonal temporal
mechanical
behavioural
what is seasonal temporal isolation
members of the two populations reproduce at different times of the year (example flowers)
what is mechanical isolation
anatomical differences may prevent mating occurring, for example, it may be physically impossible for the penis to enter the vagina in mammals
what is behavioural isolation
members of two populations have different courtship patterns
what is sympatric speciation
- occurs in the same habitat / environment / population
- mutations causes different advantage
- this leads to reproductive isolation
- different alleles are passed on
- this causes a change in frequency of alleles
- eventually different species cannot interbreed to produce fertile offspring.
