BIO 3.5

BIO 3.5

1. GENETIC DRIFT

   • cumulative changes in the allele frequency in a gene pool due to chance events
     • BOTTLENECK EFFECT
       • a severe reduction in population numbers resulting in a new population from the few surviving individuals, the allele frequency may not be representative of the original population
     • FOUNDERS EFFECT
       • a new population from only a few individuals, the allele frequency may not be representitive of the original population
     • GENE FLOW
       • caused by different kinds of barriers
         • GEOGRAPHICAL ISOLATION
           • physical barriers that prevent gene flow between populations
         • ECOLOGICAL BARRIER
           • due to lack of overlap of ecological niche, reduced opportunities for mating to occur
         • REPRODUCTIVE ISOLATION
           • reproduction between closely related species is prevented
       • exchange of alleles between populations by immigration and emigration
         • MIGRATION
           • IMMIGRATION
             • movement of individuals into a population/gene pool
           • EMIGRATION
             • movement of individualS out of a gene pool

2. SELECTION

   • NATURAL SELECTION
     • indiviuals in a population that are best suited to the environmental conditions will leave the most offspring
       • FITNESS
         • the relative breeding success of an individual, individuals that leave the most offspring in the next generation are the fittest
       • TYPES OF SELECTION
         • STABILISING SELECTION
           • favours the average phenotype over the extreme
         • DISRUPTIVE SELECTION
           • favours the extreme phenotypes over the average
         • DIRECTIONAL SELECTION
           • favours one end of a range of phenotypic variation over the other extreme and average phenotype
       • SURVIVAL OF THE FITTEST
         • foundation of natural selection, individuals best suited to environmental conditions have highest success rates of survival and reproduction
   • ARTIFICIAL SELECTION
     • occurs when people select individual organisms to breed from to produce populations with the desired traits
   • NON-RANDOM MATING
     • occurs when an individual selects another individual with a certain phenotype with which to mate

3. SPECIATION

   • ALLOPATRIC
     • emergence of new species from populations that are geographically seperated from each other
     • VICARIANCE
       • when large-scale allopatric speciation occurs as a result of a major geophysical event
         • formation of a new ocean/ river or mountain
   • SYMPATRIC
     • speciation not involving geographic isolation but biological changes resulting in reproductive isolation
   • INSTANT SPECIATION
     • generally refers to polyploidy, where a new species appears instantly

4. REPRODUCTIVE ISOLATION MECHANISMS

   • blocks the exchange of genes between species and keeps gene pools separate
     • overtime results in a new species being formed, as each isolated population develops permanent changes in its gene pool through natural selection, genetic drift, and random mutations
   • PREZYGOTIC
     • barrier to gene flow which occurs before zygote formation
     • geographical, ecological, temporal, structural/morphological, behavioural and gametic isolation
       • prevent or reduce the likelihood of genetic transfer to members of other species.
   • POSTZYGOTIC
     • barrier to gene flow which occurs after zygote formation
     • reduces the survival of hybrid zygotes or reduces the reproductive success rate of the hybrids.
       • HYBRID INVIABILITY
         • a hybrid embryo forms but its ability to survive is reduced
       • HYBRID STERILITY
         • offspring of two different species form but are infertile
       • HYBRID BREAKDOWN
         • first generation (F1) is fertile but not future generations (F2) which are inviable or sterile.

5. NZ BIOGEOGRAPHY

   • formation of the Southern Alps
     • produced two distinct climates
       • West: higher rainfall and milder winters
       • East: lower rainfall but extremes of temperature.
       • Mobile species such as birds and insects can move to where areas and climates are better for them but things like snails and plants are unable to move so have to adapt - form subspecies.
   • formation of the Cook Strait
     • Sea level rose up to 150m after the last ice age, not only separating terrestrial species but also freshwater ones as rivers now isolated on each island.
   • BIOGEOGRAPHY
     • the geographic distribution of organsims

6. PLOIDY

   • POLYPLOIDY
     • having more than two complete sets of chromosomes
       • entire set of chromosomes is duplicated
         • Triploid: 3n Tetraploid: 4n and so on
     • ALLOPOLYPLOIDY
       • a polyploid hybrid resulting from two different closely related species interbreeding and combining their sets of chromosomes
       • hybrid created is sterile, the chromosomes are not able to line up as they are different
         • allopolyploids can undergo somatic doubling
           • produces a tetraploid, making the individual fertile
     • AUTOPOLYPLOIDY
       • a species that has more than two chromosome sets all from the same species
         • A result of non-disjunction during meiosis, all chromosomes end up in one daughter cell (2n), the other cell ends up empty(n-1)
       • SOMATIC DOUBLING
         • the doubling of chromosomes in an individual derived from an interspecific hybrid that would have two different sets of chromosomes, to make it fertile
           • in the case of an autopolyploid having an uneven number of chromsomes, they cannot align and reproduce, so they double to form an even number to make the individual fertile
       • HYBRID VIGOUR
         • hybrids which exhibit improved growth or other positive phenotypes compared to either parent
   • ANUEPLOIDY
     • more than two of a particular chromosome
     • Occurs as a result of non-disjunction - this occurs during meiosis when there is a failure to separate due to the spindle not functioning properly.

7. PATTERNS OF EVOLUTION

   • DIVERGENT EVOLUTION
     • when one species evolves into two or more species
       • the new species all share a recent common ancestor
         • DICHTOMY
           • hybrids which exhibit improved growth or other positive phenotypes compared to either parent
       • generally a result of allopatric speciation
     • ADAPTIVE RADIATION
       • evolutionary diversification of related species into different environments or niches
       • rapid divergent evolution causes a large number of species to arise from a common ancestor over a short period of time
         • may be a result of new availability in a habitat or competition being removed from an environment
   • CONVERGENT EVOLUTION
     • when largely unrelated species evolve similar features
       • organisms of different species face similar selection pressures which result in similar evolutionary adaptations
       • no recent common ancestor
     • PARALLEL EVOLUTION
       • when two or more related groups evolve along similar lines independently
   • CO-EVOLUTION
     • a change in the genetic composition of one species in response to the genetic change in another species
       • predator/prey parasite/host competitive species mutualistic species

8. EVIDENCE FOR EVOLUTION

   • FOSSIL RECORD
     • relics and traces of dead plants and animals that have been mineralised in sediments
       • used to observe the rate of evolution in a species and when speciation occured
         • ANAGENESIS
           • new species evolving from an ancestral form and the ancestral form becoming extinct

9. RATES OF EVOLUTION

   • GRADUALISM
     • changes causing speciation occur over a long period of time with steady changes showing
       • intermediate forms can be observed using fossil record
       • slow changes in allele frequencies caused by different selection pressures
   • PUNCTUATED EQUILIBRIUM
     • long periods of little change in a species (stasis) interrupted by short periods of rapid speciation.
       • may be a result of allopatric or sympatric speciation
       • lack of intermediate forms in fossil records due to rapid speciation