evolution

• evolution


  descent with modification from a common ancestor
• micro vs macro evolution


  both occurs due to a change in allele frequency in a population over successive generations

  micro evolution occurs over a shorter period of time

  no new species formed for microevolution
• natural selection

  1. all organisms produce a large number of offspring, leading to an exponential increase in population IF all OS survive
  2. however, size of population remains relatively constant as many offspring die before they reach reproductive age
  3. as individuals of a species are constantly competing with each other for limited resources
  4. individuals of a population differ from each other genetically, and thus phenotypically. these variations act as a raw material for NS to act on
• 5. among variety of individuals, some will have fav characteristics that are better adapted to the environment and will be selected for by the environment, survive to reproductive age to produce viable, fertile offspring. less well adapted individuals will be eliminated

  6. individuals with fav characteristics are likely to breed successfully and produce offspring similar to themselves, thus passing on fav characteristics to offspring so that frequency of fav alleles will increase

  7. over thousands of generations, reproductive isolation can occur and a new species can form
• variation

  • phenotypic differences between individuals in the same species
  • is the raw material for NS to act on
  • arises from mutations, meiosis and SR
  • if not for variation, all organisms will either be selected for or selected against and extinction can occur
• types of NS

  directional, disruptive, stabilizing
• importance of completing antibiotics course

  ensure dosage sufficient to clear most of susceptible bacteria, leaving only antibiotic-resistant bacteria for immune system to clear
• genetic drift


  random change in AF from 1 gen to another that is not due to NS, but due to random sampling or chance events

  i)founder effect: small grp of indiv leave ancestral population, not likely to carry all alleles from ancestral population, some genes under / over represented

  ii) bottleneck effect: population size decrease drastically due to catastrophe
• why the population is the smallest unit that can evolve

  A population is a group of interbreeding individuals of the same species. Evolution is a measure of changes in allele frequencies in a population over successive generations. variation exists in a population, survivors of NS will pass on FA to next gen, overtime contri to AF change that can be measured in a population over successive generations over time, and not an in an individual, the population is the smallest unit that can evolve.
• biological


  A species is a group of organisms capable of interbreedingand producing fertile, viable offspring.

  • reproductively isolated from other species
  • A: can be interbred to see if they produce fertile, viable offspring
  • L: cannot be applied to asexually reproducing organisms and extinct species, whose breeding behavior cannot be observed
• genetic


  a species is a group of genetically compatible interbreeding organisms in a natural population that isgenetically isolated from other such groups

  • diff genetic species do not interbreed in nature
  • A: Genetic data from mitochondrial and nuclear DNA is unambiguous in deducing evolutionary relationships.
  • L: technology required to study DNA sequences is relatively expensive
• Ecological


  A species is a group of organisms sharing the same ecological niche (both the place where an organism lives and its interactions with the environment)

  • A: Every organism has a niche
  • L: Sometimes unrelated species that occupy similar niche
• Morphological 


  A species is a group of organisms sharing similar body shape, size and other structural features.

  • A: this definition can be applied to all organisms
  • L: difficult to determine the degree of difference that is required to indicateseparate species as well as what structural features should be used to distinguish thedifferences. Some organisms may be superficially similar but have different evolutionary origins. Large morphological differences can exist even within a species.
• Phylogenetic


  A species is the smallest group of organisms that share amost recent common ancestor and can be distinguished from other such groups. They occupy a branch on a phylogenetic tree.

  • A: avoid mistakenly classifying organisms based onsuperficial morphological similarities
  • L: accuracy of phylogenetic tree dependent on availability and accuracy of source data.
• speciation


  process which one or more new species arise from a previously existing species
• For speciation to occur, gene flow must be disrupted. Then evolutionary changes could occur independently in each sub population.
• allopatric speciation


  geographical isolation
• sympatric speciation


  physiological or behavioural isolation
• how speciation occurs

  1. Ancestral population was separated into 2 subpopu due to geographical/reproductive barrier
  2. The barrier prevented interbreeding and resulted in the disruption of gene flow between the 2 sub popu
  3. Each sub population was exposed to different SP in their differing niches
  4. [NS]
  5. As sub popu evolved indep of each other, their AF changed. This is because as they accumulated different genetic mutations, and were subjected to genetic drift and NS
  6. Over thousands of gens, each sub popu became two distinct, repro iso species can no longer interbreed to produce viable, fertile OS.
• The genus name always begins with a capital letter & the species name always begins with a lower case letter. Both names must be underlined separately
• Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
• Biological classification is the organization of species according to their shared characteristics in a hierarchical manner, into increasingly inclusive groups/taxons based on anatomical and more recently molecular data
• Phylogeny is the organization of species to show their evolutionary relationships
• adv of molecular methods

  • Nucleotide data can be used to compare organisms that are morphologically indistinguishable due to convergent evolution / they are closely related.
  • Specimens need not be complete or alive for comparative analysis so long as the molecules survive degradation.
  • Since all known life is based on nucleic acids, nucleotide data can be used to compare all organisms which share common genes
  • Nucleotide data is objective as molecular character states are unambiguous
• why dna yield more info than a.a

  some diff in dna seq not reflected in a.a seq due to degeneracy of genetic code
• Homology


  refers to similar anatomical & molecular characteristics found in different species due to common ancestry
• • The pentadactyl limb is a homologous structure in forelimbs of all tetrapods
  • The forelimbs have the same arrangement of bones but have different functions and superficially look different
  • The limb structure in the common ancestor was altered by natural selection in the different organisms to suit their specialised environments, resulting in variations of the pentadactyl limb structure
• • Anatomically homologous structures that are greatly reduced in size or have little to no function are called vestigial structures
  • Organisms with vestigial structures share common ancestry with organisms in which the structure is still functional
• Biogeography: the study of the past and present geographical distribution of organisms

  common ancestor establishes itself in one location and as speciation occurs, the new species disperseout of the center of origin
• molecular homologies:

  • greater the sequence similarity between homologous genes, the more closely related the 2 species are
  • Cytochrome C and p53 are homologous genes, and when expressed produce proteins that have the same function in all organisms that possess them (CA)
  • Nucleotide sequences in the ancestral genes were modified due to accumulation of mutations (NS)
• Polyploidy: 3n / 4n

  Aneuploidy: down syndrome
• How recessive alleles are preserved in a natural population

  1. heterozygote protection
  2. heterozygote adv: eg. SCA (homo rec SCA, homo dom malaria, hetero carrier)
  3. frequency based selection
• mtDNA

  • doesnt undergo recombination, any change in dna seq is due to accumu of mut over time
  • relatively fast rate of mut due to poor proof-reading mech: differences in sequence sufficient to distinguish btwn diff species and closely related indiv of the same species