paper 2: Evolution May Lead to Speciation Flashcards
how does natural selection cause populations of species to become better adapted to thier environment
- random mutation results in a new allele
- gives organism an advantage with certain selection pressure
- organisms with allele more likely to survive and reproduce
- offspring inherit advantageous allele
- allele freuence increases over time
- causing direction/ stabilising/ disruptive selection
what factors cause variation
genetics
environment
whta produces further genetic variation
- meiosis and the random fertilisation of gametes during sexual reproduction
decsribe discontinuous variation
- only discrete categories
- results from genetics only
- environment has little/ no influence
draw a graph showing discontinuous variation
describe continuous variation
- can take any value in any range
- results from many different genes
- environmental factors have a large impact
draw a graph showing continuous variation
what is a phenotype
the appearance of a characteristic due to the expression of genetic constitution and interaction with the environment
what causes variation in phenotyoe
- mutations which create new alleles which produce non-functional proteins
what is directional selection
- selection pressure that favours the extreme phenotype
give an example of directional selection
antibiotic resistance in bacteria
draw a graph showing directional selection
what happens to allele frequenceis in directional selection refering to antibiotic resistant bacteria
- resistant allele increases overtime as it survives and reproduces so gets passed down
what is stabilising selection
- selection spressure at both ends of distribution
- favours the intermediate phenotype and eliminates the extreme
example of stabilising selection
human birth mass
explain what happens to allele frequencies of stabilising selection using human birth mass
- small babies struggle to regulate body temperature due to a large SA:V ration
- large babies during birth so intermediate is favoured and normal birth mass allele frequency increases
draw a graph showing stabilising selection
what is disruptive selection
selection pressure favours both extremes of phenotype
give an example of disruptive selection
- finches with large beaks feed on large seeds and finches with small beaks feed on small seeds
what is speciation
the process through which new species arise
what is a gene pool
all alleles of all the genes in a population
what is allopatric speciation
2 populations of same species become geographically isolated from eachother so cannot interbreed
model answer for allopatric speciation
- populations of same species become geographically isolated
- they cannot interbreed so forms separate gene pools
- areas have different selection pressures
- in each population mutations occur and form new alleles
- different alleles passed onto offspring
- allele frequency chnages over time
- when barries is removed the populations cannot interbreed to produce fertile offspring
what is sympatric speciation
individuals become reproductively isolated from oher individuals in the same area
model answer for sympatric speciation
- occurs within the same area
- mutations form different alleles in population
- populations become reproductively isolated
- offspring inherit different alleles changing the allele frequency over many generations
- causes disruptive selection
- populations cannot interbreed to produce fertile offspring
what is genetic drift
in small populations, by chnace one allele is inherited more often and becomes more frequent
what is the difference between genetic drift and natural selection
- natural selection only causes alleles and phenotypes to become more common if they increase chance of survival
- genetic drift makes alleles become more common by chance
