variation and classification

• interspecific variation - variation between species
• intraspecific variation - variation within a species
• genetic variation - mixture of alleles of genes inherited affect the phenotype of an organism

  • random mutation - chromosome mutation
  • recombination of alleles - crossing over prophase 1, independent assortment, random fertilisation
• environmental variation - phenotypic variation can be caused by differences in the environment: climate, diet, lifestyle

  • etiolation - plants with little light
  • chlorosis - yellow leaves due to lack of chlorophyll, lack of magnesium in the soil
  • diet - body mass, height
• discontinuous variation

  • phenotypes fall into distinct and discrete categories
  • bar chart
  • controlled by one gene (monogenic)
  • includes codominance and multiple alleles
  • may be two epistatic genes
  • environment has little to no impact
• continuous variation

  • continuous range of values between two extremes, usually forming a normal distribution curve
  • controlled by several genes (polygenic)
  • genes tend to provide additive effect
  • smaller effects of each allele causes quantitative variation in phenotype
  • polygenic characteristics influenced by the environment
• species - group of organisms; similar in appearance, anatomy, physiology and genetics

  members of a species can breed together and produce fertile offspring
• phylogeny - the study of evolutionary relationships between species, it shows how closely related different species are. The relationships between species can be clearly displayed on a phylogenetic tree. Species are more closely related appear closer to another

  when two lines diverge = a common ancestor is now extinct
• convergent evolution - evolution of similar features in distantly related species, creates similar features that have similar form or function but have evolved separately

  adaptations are controlled by the environment, evolutionary distinct species that live in similar niches often evolve similar

  • eg fins on dolphins and sharks
  • marsupial and placental moles - different taxonomic groups
• classification - group organisms using the similarities and differences between organisms
• binomial system - a system of naming organisms using two words, the first word is the genus and the second word is the species. It is universal
• prokaryotes

  • no nucleus
  • loop of dna not arranged in chromosomes
  • naked dna
  • no membrane bound organelles
  • small ribosomes
  • free-living or parasitic
• protoctists - protoctista

  • eukaryotic
  • single celled
  • contain chloroplasts or hydrolytic enzymes
  • mostly free living
  • autotrophic/heterotrophic nutrition
• fungi

  • eukaryotic
  • single close (yeast) or mycelium
  • cell walls made of chitin
  • multinucleate
  • free living
  • saprophytic nutrition - enzymes break down matter
  • glycogen food store
• plants

  • eukaryotic
  • multicellular
  • cell walls made of cellulose
  • autotrophic nutrition
  • contains chlorophyll
  • starch food store
• animal

  • eukaryotic
  • multicellular
  • heterotrophic
  • glycogen food store
• evidence for classical classification - morphology, anatomy, behaviour and fossil record
• evidence for modern classification - embryology, scanning electron microscopy, biological molecule analysis

  • cytochrome c - protein required in respiration, compare amino acid sequence to conclude how related species are
  • dna - compare sequences for similarities
• domains :

  eubacteria became bacteria

  archaebacteria became archaea

  all the rest became eukarya
• bacteria vs Achaea

  • bacteria have different cell membrane structure
  • different enzymes for building rna
  • no protein bound to genetic material
  • different mechanism for dna replication
• Darwins observations

  • species over reproduce
  • populations tend to remain fairly stable, assuming no environmental change
  • variation within a species
  • offspring often resemble their parents - characteristics are inherited
• Darwins deductions

  • struggle for survival, individuals get eaten, die of diseases or compete for resources
  • individuals with characteristics that best adapt them for their environment are most likely to survive and reproduce
  • if these characteristics can be inherited then the organisms pass them onto their offspring
• evidence for evolution

  • fossil record - fossils show different species were alive in the past, fossilised remains show species getting more and more complex as time goes on
  • problems : incomplete, usually only harder parts will fossilise, very rare formation
• recent evidence for evolution

  • biological molecules
  • protein variation of dna and rna
  • dna sequencing
  • mitochondrial dna mutates more frequently
• adaptation - feature that enhances survival and long term reproductive success
• behavioural adaptations - an aspect of behaviour that allows it to survive where it lives

  eg migration, hibernation
• physiological adaptations - internal and biochemical features that ensure the correct functioning of cell processes

  eg antibiotic production
• anatomical adaptations - any structure that enhances the survival of the organism

  eg feathers
• natural selection

  • genetic variation
  • selection pressure
  • reproductive success
  • repeated over many generations
• genetic variation within natural selection

  random mutation cause different alleles of genes, this causes intraspecific variation

  occasionally these alleles are beneficial
• selection pressure within natural selection

  organisms have to compete for survival, selection pressures are environmental factors that determine survival and reproduction.

  can be: predators, food availability, disease
• reproductive success within natural selection

  the organisms with advantageous adaptations are more likely to survive and reproduce

  those that can reproduce will pass on alleles that code for the beneficial characteristics
• repeated over many generations within natural selection

  the process is repeated so the beneficial alleles become more frequent in the population. There fore the proportion of the population possessing the advantageous characteristic increases
• implications of evolution for human populations - pesticide resistance

  the use of pesticides creates a selection pressure for those indivdiuals with some form of resistance to the insecticide

  insects may metabolise the poison or alter receptors on cell membranes

  problems - bioaccumulation, crop loss, development of new pesticides
• stabilising selection - if the environment is stable, the same alleles will be selected for in every successive generation and the same gene pool of the population remains

  extremes of the phenotype are selected against

  intermediate phenotypes are selected for

  eg camouflage coat colour, plant height
• directional selection - if the environment changes there will be a change in the selection pressure on the population. One extreme will be selected for and the other selected against

  over time the alleles frequency shifts

  eg Darwins finches
• inbreeding - breeding of genetically similar parents
• interbreeding - 2 difference species of the same genus
• genetic drift - random fluctuations can occur in allele frequency within a population. Most likely in small populations

  randomness of reproduction, in extreme cases an allele may be eradicated entirely
• genetic bottleneck - a natural disaster or pandemic may kill a large percentage of a population

  this may lead to alleles being lost

  genetic diversity is reduced

  population increases from small gene pool