Lecture 7- the origin of species Flashcards
what does evolution require to occur?
Changes in allele and genotype frequency
what are the evolutionary changes that effect changes in allele and genotype frequency?
- genetic drift
- mutation
- gene flow
- natural selection
what is mutation?
changes in the genetic code
when is mutation more successful at causing evolution?
when it occurs in cells that produce gametes, as the mutation can be passed onto the offspring
on which genes does selection not occur on?
ones that affect the phenotype
why may mutations not be beneficial?
often organisms are already well adapted to their environments, so changes may reduce this adaptability and not be beneficial
what rate does mutation occur at?
1/100000 genes per generation, low impact on population
what is gene flow?give an example
- the genetic exchange between populations
- the movement of fertile individuals or movement of gametes (pollen) between populations
how does gene flow reduce genetic differences between populations?
there’s an increased amount of shared genetic material between the two
what is genetic drift?
the Chance alterations in the allele frequencies of populations
what are the two main mechanisms of genetic drift?
- bottleneck effect
- foundler effect
explain the bottleneck effect
- the parent population undergoes a massiv ereduction in population size, this may be as a result of a natrual disaster
- a small random assortment of survivors with random genes survive,with different allele frequencies to the prior population and some may be missing entirely
- this significantly reduces genetic diversity, and diversity may take a long time to recover after this event
explain the founder effect
- a few induviduals of a species migrate and colonize a new region (eg. a volcanic island) ,and become founders of this new isolated population
- this new gene pool differs significantly to the new population
- rare alleles may be significant as they will be the genes passed on the future generation
- this leads to a loss of genetic variability and non random distribution of genes
how does genetic drift impact a species ability to adapt to an environment?
it leads to a loss of genetic variation. evolution requires variation in order for adaptation to occur, so this impacts how well suited these organism are to their environment
explain natural selection in genetic terms
occurs from individuals passing on alleles to the next generation, that differ in frequency to the current one
what are the three modes of natural selection?
- stabilizing
- diversifying
- directional
what is directional selection?
- when the conditions favour individuals exhibiting one extreme of the phenotype range.one sided outlier advantage
- common in changing environments
which method of natural selection is a one sided outlier advantage?
directional
what is disruptive selection?
when the extremes of the phenotype range are favored over the intermediate ones
what is stabilizing selection?
-when the intermediate phenotype variants are favored over the intermediate ones
what is k selection? what is it dependent on
- k selection occurs in high density populations, where traits that use lesser resources are favored
- its density dependent
what is r selection?
at low density populations, with no pressure on resources, selection favors traits that allow rapid reprouduction
which one, r or k selection, favours traits that allow rapid reproduction?
r selection
in what type of population does k selection occur?
in a high density one with lesser access to resources
what is allopatric speciation?
- changes in environment cause a population to be isolated
- this population then evolves in isolation, causing division into a new species
what is sympatric speciation?
- occurs in geographical overlapping populations
- changes in environment cause selection to act upon some individuals
- gene flow is reduced (eg. by chromosome mutations or via non random mating)
- the two continue to evolve until they can no longer interbreed
which type of speciation occurs in geographically overlapping populations?
sympatric speciation
explain the concept of a ring species
a ring species is where two species within the same environment become to genetically different to interbreed, however they are connected by a geographical ring of species that cannot interbreed
what is a reproductive barrier of sympatric speciation?
once the species have evolved they can no longer interbreed, as they are now too distantly related
what is the difference between a prezygotic and a post zygotic barrier?
prezygotic barrier prevent fertilisation from occurring, postzygotic barriers prevents offspring from being fertile
what does post zygotic barriers refer to?
the non viable offspring produced as a result of hybridisation between two species.
what is hybrid inviability?
a postzygotic barrier. when the offspring dies as an embryo
what is hybrid sterility?
when the offspring produced by hybridisation is unable to breed(sterile). this is a postzygotic barrier
what is hybrid breakdown?
the first generation of hybrids (produced by two species interbreeding) is able to produce offspring. however, the second generation is infertile and cannot breed with similar crosses, or backcrosses to the parent species
what are the three postzygotic barriers?
- hybrid inviability
- hybrid breakdown
- hybrid sterility
what are the five forms of prezygotic barriers?
- habitat isolation
- behavioural isolation (eg. different mating calls)
- temporal isolation (mates in different seasons)
- mechanical isolation
- genetic isolation
what is phyletic gradualism?
a slow but steady rate of evolutionary change. small changes accumulate steadily over long periods of time, resulting in speciation
what is punctuated equilibrium?
the theory of evolution that species show no evolution for long periods of time, and then have rapid burst of speciation.
which rate of evolution theory does adaptive radiation relate to?
punctuated equilibrium
how can genetic variation be described on a gene level?
The average amount of loci that are heterozygous
what does the harvey Weinberg equilibrium state?
that allele and genotype frequencies will remain fixed in a population provided there is no evolutionary influence
which evolutionary force results in adaptive evolution? why?
- natural selection
- the other three can introduce harmful genes into a population, whereas only beneficial traits survive selection in natural selection
what is frequency dependant selection?
where the fitness of a phenotype depends on how prevalent it is in a population
