Modern Classification Techniques

Taxonomy - 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 (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 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.

Carbon Dating Half - life Useful range C14 ----------> 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 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” 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)

(ii) comparative anatomy Comparing 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 Cladistics

Phylogeny and Phylogenetic Tree A hypotheses about the evolutionary history of an organism. The roots of the phylogenetic tree show the oldest ancestral species. The upper ends of the branches show current species. Each fork represents the adaptation that changed the common species into two new species. Use the example on page 116.

Cladistics Cladistics is a classification scheme based on phylogeny. A Cladogram is similar in design to the phylogenetic tree, but used to test hypotheses about how the branches could have occurred. Which of the following 3 cladograms makes the most sense.

Homework PAGE 121: 1, 2, 5,6, 9 (paragraph), and 12