"The affinities of all the beings of the same class havesometimes been represented by a great tree... Asbuds give rise by growth to fresh buds, and these ifvigorous, branch out and overtop on all sides many afeebler branch, so by generation I believe it has beenwith the great Tree of Life, which fills with its deadand broken branches the crust of the earth, andcovers the surface with its ever branching andbeautiful ramifications."Charles Darwin, 1859Charlie sure could spit out a quotable piece of writing
D.5.1 Outline the value of classifying organisms Identification of Organisms Unknown organisms are easily identified if data about organisms is organised. Classification allows for the creation of keys. Remember 5.5 Classification?
Evolutionary Links Classification allows us to see evolutionary relationships. Organisms that are grouped together share a lot of similar features (homologous structures). These shared characteristics help us see how organisms have evolved from a common ancestor. e.g. Llamas were originally compared to sheep but a study of their morphology later placed them in the camel familyhttp://www.flickr.com/photos/mrapplegate/2423991076/ http://www.flickr.com/photos/doug88888/3458057235/
Prediction of CharacteristicsCharacteristics that are shared by organisms within agroup would be expected to be found in otherspecies that are closely related. e.g. no doubt more fossils that can be categorised in the Homo genus will be found. We can expect them to have relatively big brains (crazy “Hobbit” finds excepted!) http://commons.wikimedia.org/wiki/File:Hominins_2002.png
D.5.2 Explain the Biochemical evidence provided by the universality of DNA and proteinstructures for the common ancestry of living organisms 1) All known organisms use DNA as genetic material The genetic code is universal. Gene sequences inserted in different organisms express the same proteins http://commons.wikimedia.org/wiki/File:Bdna.gif
2) The same 20 amino acids are used to make all proteinshttp://commons.wikimedia.org/wiki/File:Protein_primary_structure.svg
3) Most amino acids can exist in left or right- handed forms, i.e. as mirror images Yet all living things use left-handed amino acids It is believed that this was a chance occurrence in the oldest common ancestor The panspermia hypothesis may help explain this asmore amino acids found in meteorites are left-handed than right-handed http://commons.wikimedia.org/wiki/File:Chirality_with_hands.jpg
4) Cytochrome c is a protein involved in theelectron transport chain.It consists of 100-104 amino acids and isfound in plants, animals, and manyunicellular organismsIt is too complex to have evolvedindependently and so must come from acommon ancestor Further evidence of common descent http://en.wikipedia.org/wiki/File:Cytochromec.png
D.5.3 Explain how variations in specific molecules can indicate phylogeny Taking the example of the protein cytochrome c. It is not identical in all species because single point mutations in the DNA that codes for it can lead to different amino acids making up the protein. Both humans and chimpanzees have the identical cytochrome c molecules, while rhesus monkeys share all but one of the amino acids: the 66th amino acid is isoleucine in the former and threonine in the latter. This suggests that humans and chimpanzees are I didn’t want to be more closely related to each other than to rhesus monkeys closely related to stinking humans anyway! http://www.flickr.com/photos/stuffinhergoose/571672799
TOK Read this article: Closer to man than ape What reasons are given for including chimps in genusHomo? Do you think humanswill ever be reclassified Pan?
This is part of a molecularphylogeny of all of the livingprimates.It clearly shows chimpanzees (Pan)as being more closely related tohumans than to gorillas.It was made bycomparing 34,927base pairssequenced from54 genes takenfrom each of asingle species ineach genus.
D.5.4 Discuss how biochemical variations can be used as an evolutionary clock An evolutionary clock involves calculating the time since species diverged by comparing the number of differences in their DNA and/or protein sequences. Scientists who originated the idea calibrated the amino acid differences in haemoglobin with times derived from the fossil record. http://commons.wikimedia.org/wiki/File:Nature_Clock.gif
The assumption is that these changes occur at a regular rate.(which may not always be the case)Therefore if species A had 5 differences from species B and 10differences from species C, then the lineages for A and C musthave split twice as long ago as for A and B C B A Time
D.5.5 Define clade and cladistics Cladistics (From the ancient Greek for "branch") is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants (and nothing else). Wikipedia http://www.flickr.com/photos/aussiegall/4149475009/
For example, birds, dinosaurs, crocodiles, and all descendants (living http://www.flickr.com/photos/kev http://www.flickr.com/photos/mo http://www.flickr.com/photos/tam or extinct) of their om/photos/emraya/2929959881/ most recent common ancestorform a clade Wikipedia
Characteristics change over time,thus the amount of change canhelp determine relationships Groups of organisms are descended from a common ancestor There is a branching pattern in the evolution of species and when a split occurs, two distinct species eventuate.
Hair Shelled eggsEach clade Amniotic Eggis determined by Four Limbscommon characteristics Bony Skeletonof its members that aredifferent from that of the Vertebrateother species from whichit has diverged http://bridgeurl.com/xrmmmk/all
These traits which tie the clades together are called shared derived characters http://www.flickr.com/photos/29448992@N08/2970804257/
D.5.6 Distinguish, with examples, between analogous and homologous characteristics Homologous structures are inherited from a common ancestor http://www.flickr.com/photos/opoterser/4189239614/
e.g. The fly on the previous page andthe mosquito on this page havemouthparts adapted to their foodsources but the basic componentswere inherited from a commonancestor Other examples include pentadactyl limbs and finches’ beaks http://www.flickr.com/photos/kclama/102002644/
Analogous structures have similar form and function due to convergent evolution, they do not stem from a common ancestor Bats… http://www.flickr.com/photos/tjt195/105694980/
…and bugs all have wings for flight that evolvedindependently Other examples include: -Streamlined shape for dolphins , sharks and ichthyosaurs -Long snout and tongue for capturing ants on the anteater and echidna http://www.flickr.com/photos/hhoyer/3758550410/sizes/o/in/photostream/
D.5.7 Outline the methods used to construct cladograms and the conclusions that can be drawnfrom them ANDD.5.8 Construct a simple cladogram • These two cladograms are identical (although they don’t look it) • The shape and the order of the terminal nodes does not matter. • The only information to be gathered from the cladograms below is the order of nesting of sister clades and the relative relatedness of species http://commons.wikimedia.org/wiki/File:Identical_cladograms.svg
Out group: Defines the ancestral Terminal nodes Sister clades: have a characters common ancestorHuman Chimp Gorilla Chimp Human Gorilla Nodes: Common ancestors Root
Branches on acladogram can bescaled or unscaled.If the branches arescaled, the lengthof the branch oftenindicates how muchevolutionarychange hasoccurred in aspecies since it splitfrom it’s sister cladeat the last node http://www.ncbi.nlm.nih.gov/About/primer/phylo.html
Rooted cladogramsshow evolutionaryrelationships.Unrooted trees justshow therelationshipsbetween clades http://www.ncbi.nlm.nih.gov/About/primer/phylo.html
Cladograms are made by compiling data on homologous characteristics shared by species. These characteristics can be structural, physiological and/or biochemical. With increasing taxa comes increasing complexity.Number of taxa 23 4 5 6 7 8 9 10 NPossible numberof rooted 1 3 15 105 945 10,395 135,135 2,027,025 34,459,425 1*3*5*7*...*(2N-3)cladograms So software is often used to find the best possible tree that has the fewest evolutionary steps.
This cladogram forbacteria iscomputergenerated
1) Compile a table of the characters being compared Characters Shark Frog Kangaroo Human Vertebrae X X X XTwo pairs of limbs X X XMammary glands X X Placenta X Modified from: http://www.bu.edu/gk12/eric/cladogram.pdf
2) Use the data to constructa Venn diagram, Vertebrae:Start with the Sharkcharacteristic Two Pairs ofshared by all Limbs: Frogtaxa in the Mammarybiggest circle Glands:and work Kangarooinwards Placenta: Human
3) Convert the Venn diagram into a cladogram Shark Frog Kangaroo Human Placenta Mammary Glands Lungs Vertebrae
Now you try! Make a Venn diagram for this data.Characters Sponge Jellyfish Flatworm Earth- Snail Fruit fly Starfish Human wormCells with flagella X X X X X X X XSymmetry X X X X X X XBilateral symmetry X X X X X XMesoderm X X X X XHead develops first X X XAnus develops first X XSegmented body X XCalcified shell XChitinous Exoskeleton XWater Vascular system XVertebrae X
It should look Cells with flagella: Spongesomething Symmetry: Jellyfishlike this: Bilateral symmetry: Flatworm Mesoderm Head develops first Anus develops first Segmented Body: Earthworm Water Calcified Vascular Vertebrae: Shell: system: Human Chitinous Snail Starfish exoskeleton: Fruit fly now make the cladogram
It should look something like this: Flat-Sponge Jellyfish worm Snail Earthworm Fruit fly Starfish Human Calcified Water shell Chitinous vascular shell system Vertebrae Segmented body Head develops first Anus develops firstSome of thecharacteristics in thedata table were unnecessary Mesodermfor the construction of this Bilateral symmetrycladogram. Symmetry FlagellaCan you identify them?
Unnecessary to use two characteristics to differentiate between Starfish and Human. Either would do the trick Flat-Sponge Jellyfish worm Snail Earthworm Fruit fly Starfish Human Calcified Water shell Chitinous vascular shell system Vertebrae Segmented body Head develops first Anus develops firstUnnecessary to differentiate Snail.Snail is the only species with head Unnecessary to use Mesodermdevelops first and without two characteristics Bilateral symmetry to split lineagessegmented body Symmetry Flagella
D.5.9 Analyse cladograms in terms of phylogenetic relationships A B C D Of the three nodes, 3 is most recent and 1 3 occurred earliest. Node 3 is the most recent 2 common ancestor for C and D Node 2 is the most recent common 1 ancestor for B and C Node 3 is the common ancestor of all taxa And so on…
D.5.10 Discuss the relationship between cladograms and the classification of living organisms Mammals have the unique homologous characteristic of producing milk They form a clade http://www.flickr.com/photos/chavals/3720930469/
Likewise, birds share thecommon characteristic offeathersThey too form a clade http://www.flickr.com/photos/bestrated1/47581481/
LizardTortoise Reptiles, as a group, consist of the crocodilians, lizards and snakes, tortoises and turtles and tuatara. However, they are not a clade. One of them is actually more Tuatara closely related to birds.Crocodile Care to guess which one? http://www.flickr.com/photos/audreyjm529/155024495/ http://www.flickr.com/photos/mg-muscapix/3288435589/ http://www.flickr.com/photos/8363028@N08/2665814123/ http://www.flickr.com/photos/sidm/5253662054/
Crocodiles are more closely related to birds than to lizards!Monophyletic: A recent common ancestor and all it’sdescendantsParaphyletic: Does not include all descendants from acommon ancestorPolypheletic: A group of organisms that does not What this doesn’tinclude the most recent common ancestor show is that birds are the last descendants of the dinosaurs! http://en.wikipedia.org/wiki/File:Phylogenetic-Groups.svg
*ornithologists study birds, herpetologists study amphibians and reptiles‘herp’ is a polyphylatelic grouping whereas birds are monophylatelicFish are paraphylatelicDinosaurs are paraphylatelic http://xkcd.com/867/
Further information: ↑An excellent series that covers most of the content ↑The tree of life ↑Sir David Attenborough ↓Amazing site, not to be missed! + BBC = Brilliant