Topic 2: Community of life on Earth Flashcards
define microevolution
refers to the small-scale variations of alleles, in which the descendant is of the same taxonomic group as the ancestor
define macroevolution
the variation of allele frequencies at or above the level of species over geological time - results in the divergence of taxonomic groups
what is evolutionary radiation?
an increase in taxonomic diversity or morphological disparity / rapid increase in the diversity of a clade
define extinction
the reduction of a species to zero individuals
define mass extinction
widespread event defined as a loss of 75% of all species in existence across the planet (over a “short” geological period)
what is comparative genomics
field of biological research in which the genomic sequences and associated gene products of different species are compared using computer-based analysis
define natural selection
the mechanism by which evolution occurs; descent with modification
explain natural selection using the two key terms
individuals that are better suited to the environment have higher VIABILITY and are therefore more likely to survive and have higher FECUNDITY (ability to produce offspring)
what happens to ‘selected traits’
will become more prevalent in the population
what is positive selection
-type of selection pressure
- favours a particular allele, resulting in an increase in frequency
what is negative selection
-type of selection pressure
- acts against a particular alleles, resulting in a decrease in frequency
what are the three types of phenotypic selection
- stabilising selection
- directional selection
- disruptive selection
define stabilising selection
intermediate phenotypes are better suited to environment over extreme phenotypes
- tends to narrow (stabilise) the normal curve, leading to a decrease in genetic variance –> more common when environmental conditions are stable and extreme phenotypes are disadvantageous
define directional selection
occurs when one extreme phenotype is better suited to the environment over all other phenotypes
- shifts the normal curve towards the favoured phenotype - also leads to reduced genetic variation
- (individuals with a moderate phenotype will remain within the population)
- occurs due to gradual or sustained change in environmental conditions
define disruptive selection
- individuals at either end of the ‘normal range’ are favoured over individuals in the middle (both extremes)
- leads to bimodal spread - giving rise to increased genetic variation in two distinct pop.s
what is gene flow
(migration)
- genes flow between populations
- alleles are added/ removed from gene pool due to movement of fertile individuals between populations
what is genetic drift
when chance or random events cause unpredictable changes in allele frequencies from one generation to the next
- founder effect + bottleneck effect are the mechanisms that drive this
explain the founder effect
- colonising chance event
- small group of individs are separated from the larger OG pop. and colonise a new area
- this smaller pop. doesn’t have the same diverse gene pool as the OG - resulting in dif. allele freqeuncies
explain the bottleneck effect
- catastrophic chance event
- OG pop is significantly reduced in number - leading 2 smaller gene pool and large decline in allele frequency
- reduced genetic variation– predisposes species to the risk of extinction
‘recall that speciation and macroevolutionary changes result from an accumulation of microevolutionary changes’
microevolution - observed thru genetic and phentypic changes – lead to new variation but no new species
macroevolution - changes occur over extended period - give rise to a new species (speciation)
microevolution + time =
macroevolution
what is divergent evolution
process by which distinct species arise from a common ancestor (speciation)
- isolated populations experience dif selective pressures - drives different adaptations
what is convergent evolution
different, unrelated species evolve from their respective ancestral species to have similar analogous structures that perform comparable functions
- exposed to similar selective environmental pressures
- still remain different species
what is parallel evolution
two species w/ a common ancestor evolve similar traits independent of one another
- similar selective pressures post separation
what is coevolution
the influence of species on each other and their evolution
- dif species evolve in tandem by exerting selection pressures on each other
what does allopatric mean
- speciation - occurs as a result of geographic isolation separating pop.s of a species (e.g. mountain or river)
- leads to reproductive isolation - where alleles are no longer exchanges between pop.s
what is parapatric speciation
occurs when pop/s from the same species become reproductively isolated without geographical separation - while continuing to exchange genes
- signif. variation in habitat conditions
what is sympatric speciation
when pop.s from the same species become reproductively isolated and diverge w/out geographical separation
- can occur via temporal (time) isolation (e.g. breeding times dont align with each other)
define spatial isolation
any form of isolation that leads to physical separation (e.g. natural disasters)
what is habitat fragmentation
- the breakup of a species’ territory
- isolated gene pools - preventing exchange of alleles and results in genetic drift
what is geographical isolation
- pop. separated by physical barriers
what is temporal isolation
- isolated in time
- individs prevented from mating because they breed at dif times
what is reproductive isolation
any form of isolation that prevents gene flow
- sptial and temporal both result in this
- can also link to behavioral isolation
what does SNPs stand for/ mean
Single Nucleotide Polymorphism
- a point mutation (single base) in a segment of DNA that occurs in MORE THAN 1% of the pop.
why dont SNPs impact cellular function
- mostly occur in the introns (DNA between genes) and therefore has little effect on cellular function
- as a result - not ‘selected’ out of the population and can be used to determine the timing of splits between species
