5.3: Classification & biodiversity

Charles Darwin quote

Why classify?

Evolutionary Links: Species that are in the same group probably share characteristics because they have evolved from a common ancestor, so classification can be used to predict how they evolved.

Species classification: finding out how life forms are grouped together helps us to identify an unknown organism.

First name always capitalised = genus Binomial nomenclature – process of naming organisms using two names e.g Homo sapiens Rules First name always capitalised = genus Second name always begins with a small letter = species Always use italics or under line the name Carl Linnaeus (Swiss naturalist) created this system 1735 Understanding the biosphere Show evolutionary links Predicting shared characteristics

Organisms can be categorised in other ways Can you think of any? Feeding habits Habitat Daily activity Risk (venom/non-venomous) Anatomy

Kissing Pretty Cute Otters Feels King Phillip Came Over For Good Soup Blue Whale Coast Redwood Kingdom Phylum Class Order Family Genus Species Animalia Chordata Mammalia Cetacea Balaenopteridae Balaenoptera musculus Plantae Coniferophyta Pinopsida Pinales Taxodiaceae Sequoia sempervirens Kissing Pretty Cute Otters Feels Gross Sometimes King Phillip Came Over For Good Supper

Dichotomous Key Review

Video http://www.youtube.com/watch?v=ooLr8d_pDBc http://www.youtube.com/watch?v=mD94D0KAn2U&feature=player_detai lpage

Similarities between living things: All us DNA (or RNA) as their genetic material

Similarities between living things: All use the same 20 amino acids in their proteins

Similarities between living things: All use left, and not right-handed amino acids

Examples of Similarities

Phylogeny-- Tracing evolutionary links and its origins Phylogeny is the evolutionary history of a species or group of related species

The phylogeny of many groups has been studied: Comparative anatomy of fossils by comparing the structure of protein or other biochemicals

Differences in base sequence of DNA and therefore amino acid sequence of proteins accumulate gradually over long periods of time. There is evidence that the differences accumulate at roughly a constant rate. They can therefore be used as evolutionary clocks.

D5.4 Discuss how biochemical variations can be used as an evolutionary clock

D5.4 Discuss how biochemical variations can be used as an evolutionary clock Over the course of millions of years, mutation may build up in a given period of time For example, the gene that codes for the protein alpha-globin (part of hemoglobin) experiences base changes at a rate of 0.56 changes per base per billion years. If this rate is reliable, the gene could be used as a molecular clock.

Molecular Evolution Clocks: When a stretch of DNA does indeed behave like a molecular clock, it becomes a powerful tool for estimating the dates of lineage-splitting events. When a stretch of DNA does indeed behave like a molecular clock, it becomes a powerful tool for estimating the dates of lineage-splitting events. For example, imagine that a length of DNA found in two species differs by four bases (as shown below) and we know that this entire length of DNA changes at a rate of approximately one base per 25 million years. That means that the two DNA versions differ by 100 million years of evolution and that their common ancestor lived 50 million years ago. Since each lineage experienced its own evolution, the two species must have descended from a common ancestor that lived at least 50 million years ago.

Molecular Evolution. For example, imagine that a length of DNA found in two species differs by four bases (as shown below) and we know that this entire length of DNA changes at a rate of approximately one base per 25 million years When a stretch of DNA does indeed behave like a molecular clock, it becomes a powerful tool for estimating the dates of lineage-splitting events. For example, imagine that a length of DNA found in two species differs by four bases (as shown below) and we know that this entire length of DNA changes at a rate of approximately one base per 25 million years. That means that the two DNA versions differ by 100 million years of evolution and that their common ancestor lived 50 million years ago. Since each lineage experienced its own evolution, the two species must have descended from a common ancestor that lived at least 50 million years ago.

Molecular Evolution. That means that the two DNA versions differ by 100 million years of evolution and that their common ancestor lived 50 million years ago. When a stretch of DNA does indeed behave like a molecular clock, it becomes a powerful tool for estimating the dates of lineage-splitting events. For example, imagine that a length of DNA found in two species differs by four bases (as shown below) and we know that this entire length of DNA changes at a rate of approximately one base per 25 million years. That means that the two DNA versions differ by 100 million years of evolution and that their common ancestor lived 50 million years ago. Since each lineage experienced its own evolution, the two species must have descended from a common ancestor that lived at least 50 million years ago.

Molecular Evolution. Since each lineage experienced its own evolution, the two species must have descended from a common ancestor that lived at least 50 million years ago. When a stretch of DNA does indeed behave like a molecular clock, it becomes a powerful tool for estimating the dates of lineage-splitting events. For example, imagine that a length of DNA found in two species differs by four bases (as shown below) and we know that this entire length of DNA changes at a rate of approximately one base per 25 million years. That means that the two DNA versions differ by 100 million years of evolution and that their common ancestor lived 50 million years ago. Since each lineage experienced its own evolution, the two species must have descended from a common ancestor that lived at least 50 million years ago.

A

IB Practice Test Question 1 Define the term clade. (1)

IB Practice Test Question 1 -- Answer A clade is a group of related organisms sharing a common ancestor / a group of organisms containing an ancestor and all of its descendants

IB Practice Test Question 2 Suggest two reasons for using cladograms for the classification of organisms.(2)

IB Practice Test Question 2 -- Answer Methods used to prepare cladograms use a different approach from traditional classification/taxonomy; Cladograms show ancestral relationships; Cladograms reflect how recently two groups shared a common ancestry; cladograms are (objective/accurate because they are usually) based on molecular differences (e.g. differences in DNA/ RNA Proteins); Cladograms should be considered as a good complement to traditional classification;

IB Practice Test Question 3 Using examples, distinguish between analogous characteristics and homologous characteristics.(4)

IB Practice Test Question 3 -- Answer Analogous Structures: [2 max] similar structures but different (evolutionary) origins / different basic structure but same function; e.g. vertebrate and invertebrate eyes / insect and human legs; Accept any other valid example. Homologous Structure: [2 max] structures are of similar origin / same basic structure but different functions; e.g. pentadactyl limbs in vertebrates; Accept any other valid example.

IB Practice Question 4 The cladogram below shows the classification of species A to D. Deduce how similar species A is to species B, C and D. (2)

IB Practice Question 4 -- Answer A is most similar to B; A is equally similar to C and D; A is least similar to both C and D;

IB Practice Test Question 5 Outline the evidence provided by DNA for the common ancestry of living organisms. (2)

Practice Test Question 5-- Answer all living organisms use DNA as genetic/hereditary material; genetic code is universal (e.g. nitrogenous bases code for proteins); The idea that mutations accumulate gradually in DNA; and thus the more differences there are in DNA between species the longer the time it has been since those species shared a common ancestor;

Discuss the relationship between Cladograms & Classification: Classification traditionally based on morphology/ physical characteristics ; While Cladistics is based on molecular differences/base sequences/amino acid sequences. This is a strength of cladistics because it maintain objectivity; Cladistics is based on probability but improbable events do occur, so relationships can be wrong; and this is thus a weakness of cladistics; Clades includes ancestral species/descendants from that species; The Members of clade share set of features not found in more distant relatives; Cladogram is a tree-like diagram where nodes/branches represent the splitting of (two) new groups from a common ancestor; Different cladograms can represent same relationships in a group; Cladogram timescale not necessary; Classification based on cladograms is often same as traditional classification; However, in some groups, cladograms have led to revised classification;

Three domains Bacteria, Archaea & Eukaryota Organisms used to be classified as prokaryotes and eukaryotes, but this is now thought to be limiting.