Modern Classification Techniques. Taxonomy - the science of taxonomy also involves other biological sciences such as evolution - taxonomy also attempts.

Modern Classification Techniques

TaxonomyTaxonomy - the science of taxonomy also involves

other biological sciences such as evolution

- taxonomy also attempts to determine the evolutionary history of groups of organisms

- scientists compare characteristics of different species living today with each other and with extinct species

- there are several different types of evidence that scientists can use to classify organisms and study evolutionary relationships

Evidence Used Evidence Used

(i) radioactive dating(ii) comparative anatomy ( Structural Info.)(iii) comparative embryology(iv) biochemical information ( DNA / Proteins ) (v) cellular structure(vi) behavior

(i) Radioactive Dating fossils are dated either through

determining the relative age or finding an absolute age.

relative age - sedimentary rock forms in layers so the age of each layer can be determined in relation to each other the oldest layers are found at the

bottom, and the younger layers are on top.

the age of a fossil can be approximated by the rocks layer it is found in.

Absolute AgeAbsolute Age- The absolute age of a fossil or rock

can be found through radioactive dating.

A radioactive isotope (atom with additional neutrons) breaks down into a new element at a known rate called a half-life (a half-life is the time it takes for ½ of a radioactive sample to break down). Page 113. Page 113.

Carbon Dating Half - life Useful rangeC14 ----------> C12 5730 yrs 60 000 yrs

note: for fossils too old for carbon dating, an isotope with a longer half - life must be used:

Isotope half - life

U235 700 million years

K40 1.25 billion years

U238 4.5 billion years

Try ThisTry This

Sample Problem:

If you had a fossil with 2 units of C14 left in it and you determined that in the living organism (or one that is similar) has 16 units of C14, you could use one of the following methods to find the absolute age of the fossil:

Method 1:

1. Determine amount of C14 left in fossil.

2. Determine amount of C14 in a living organism of the same size and type living today.

3. Calculate the number of half-lives needed to reduce the C14 in the living organism to the amount that is left in the fossil.

4. Multiply by the half - life ( in this case, 5730 years ) to determine the age of the fossil.

““MATH”MATH”

Method 2: N = No (½) t/H

where: - N = units in the fossil - No = units in the

living organism - H = the half – life - t = time ( this will

most likely be the one you will be finding)

2 = 16 (½)t/ 5730

1/ 8 = (½)t/ 5730

(½)3 = (½)t/ 5730

3 = t/ 5730

t = 3 x 5730

(ii) comparative anatomyComparing the anatomy of organisms indicates a

common ancestry because of:

homologous structures - structures having a common ancestry but with different uses in various species. Eg. Similar bone structure of the forelimb of

a bat, whale, horse and human suggests these different species have a similar evolutionary origin. Page 113,114 & 664

- analogous structures - body parts of organisms that do not have a common evolutionary origin but perform similar functions. Eg. insect wings and bird wings are

similar in function but not in structure. Page 665

- vestigial organs - small or incomplete organs ( or bones ) that have no apparent function in one organism but do have a function in another species. This indicates evolutionary origin from a common ancestor. Page 665 Eg. Human ear muscles, Human appendix, Hip

bones in whales, Human tail bone, Leg bones in snakes, and Forelimbs in the flightless ostrich

iii) Comparative Embryology

Comparing the embryos of organisms can indicate a common ancestry with other types of living organisms because of similar stages of embryonic development. (eg. gill slits and tail in human embryos

indicates humans share common ancestry with birds, reptiles and fish) Page 665

(iv) biochemical information ( DNA / Proteins )

Comparing the biology of one species with another at the molecular level (DNA & Proteins) can indicate a common ancestry. Page 115

- human proteins (amino acid sequences) have more in common with chimpanzee proteins than frog proteins.

- pig or beef insulin is similar enough to humans that it can be used to treat human diabetes.

(v) cellular structure

Studying structures of cells gives clues to their evolutionary history. - Remember only two basic types of cells prokaryotic and eukaryotic (review p. 106)

- fossil evidence has shown the first life forms were prokaryotic (similar in appearance to bacteria) and existed approximately 3.5 billion years ago

-eukaryotes appeared only about 1.5 billion years ago- multicellular organisms only 700 million years ago

(vi) behavior- how organisms are adapted in how they

respond to their environment is called behavioral adaptations - eg. include migration, courtship displays,

foraging behavior

- it is believed that these adaptations have evolved in response to changes in environmental conditions as continents formed and moved millions of years ago

- the favorable adaptations were passed on to the offspring

- note: Biofact p.706

How have classification systems improved as a result of these modern techniques?

- through the use of these techniques, organisms once thought to be closely related, have been found not to be related and vise versa.

Phylogeny and CladisticsPhylogeny and Cladistics

Phylogeny and Phylogenetic Phylogeny and Phylogenetic TreeTree A hypotheses about the evolutionary A hypotheses about the evolutionary

history of an organism.history of an organism. The roots of the phylogenetic tree The roots of the phylogenetic tree

show the oldest ancestral species.show the oldest ancestral species. The upper ends of the branches show The upper ends of the branches show

current species.current species. Each fork represents the adaptation Each fork represents the adaptation

that changed the common species that changed the common species into two new species.into two new species. Use the example on page 116.Use the example on page 116.

CladisticsCladistics

Cladistics is a classification scheme Cladistics is a classification scheme based on phylogeny.based on phylogeny.

A A Cladogram Cladogram is similar in design to is similar in design to the phylogenetic tree, but used to the phylogenetic tree, but used to test hypotheses about how the test hypotheses about how the branches could have occurred. branches could have occurred.

Which of the following 3 cladograms Which of the following 3 cladograms makes the most sense.makes the most sense.

HomeworkHomework

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