TOPIC 5.4 - CLADISTICS
5.4 A Clades & Cladograms
https://upload.wikimedia.org/wikipedia/commons/thumb/4/46/clade-grade_ii.svg IB BIO 5.4 3 U1: A clade is a group of organisms that have evolved from a common ancestor. Cladistics is a system of classifying organisms based on shared characteristics derived from common ancestry. A clade is a group of organisms that evolved from a common ancestor and are related. Cladistics Clade
https://s-media-cache-ak0.pinimg.com/originals/f4/b2/db/f4b2dba017458b6e6a90f7633dcde5f2.jpg IB BIO 5.4 4 Clades include all species U1: A clade is a group of organisms that have evolved from a common ancestor. currently alive, together with their ancestral species and any species that evolved and became extinct. Some clades can include many species, while others can have just a few. Cladistics The Ginkgo biloba is the only member of its clade while birds form a large clade with thousands of members. Clade
http://science.kennesaw.edu/~jdirnber/bio2108/lecture/lecphylogeny/26_labeled_images/26_15parsimonyexample_4-l.jpg IB BIO 5.4 5 U2: Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein. It is not always clear whether species evolved from a common ancestor and if they should be included in the same clade. DNA or amino acid sequences can be used to determine relatedness.
http://science.kennesaw.edu/~jdirnber/bio2108/lecture/lecphylogeny/26_labeled_images/26_15parsimonyexample_4-l.jpg IB BIO 5.4 6 U2: Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein. The graph to the left shows the differences in traits between a set of organisms. Quantifying these differences can be used to construct a basic cladogram. The same procedure is used with DNA and amino acid sequences.
http://faculty.uca.edu/johnc/cladogram_c.jpg IB BIO 5.4 7 U3: Sequence differences accumulate gradually so there is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor. Changes in DNA and protein sequences are the result of mutations. These occur at a roughly constant rate and accumulate over time. This means DNA can be used as a molecular clock. By observing the differences between DNA sequences, scientists can estimate the point at which populations diverged.
http://schoolbag.info/biology/living/living.files/image478.jpg IB BIO 5.4 8 U3: Sequence differences accumulate gradually so there is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor. As shown here, the use of DNA as a clock can help in the constructing a cladogram of species. This cladogram shows the timeline of divergence of members in the Felidae (cat) family.
https://s3.amazonaws.com/classconnection/216/flashcards/4943216/jpg/26_11bconstructphylotree-l-14925fc89025187f6f6.jpg IB BIO 5.4 9 U5: Cladograms are tree diagrams that show the most probable sequence of divergence in clades. Cladograms are tree diagrams based on similarities and differences between clade species. They show the most probable sequence of divergence in clades. Cladogram
http://www.vanderbilt.edu/peabody/novick/cladograms.jpg IB BIO 5.4 10 U5: Cladograms are tree diagrams that show the most probable sequence of divergence in clades. The structure of cladograms is now determined by computer programs. They calculate how species could have evolved with the fewest number of changes in DNA or protein sequence Cladogram
https://s3.amazonaws.com/classconnection/216/flashcards/4943216/jpg/26_un02summary_c1-l-14925fd281b24aa1cdf.jpg IB BIO 5.4 11 U5: Cladograms are tree diagrams that show the most probable sequence of divergence in clades. Branch points in cladograms are called nodes. These points represent when a single species branched into multiple. Cladogram Node
http://d3rzbccgedqypw.cloudfront.net/content/jbjsam/91/supplement_4/26/f1.large.jpg IB BIO 5.4 12 Applications A1: Cladograms including humans and other primates. Cladogram Humans can also be studied using cladograms. DNA analysis has shown that our closest relatives are the bonobo and chimpanzee. The red box to the left shows the clade of primates.
http://genealogyreligion.net/wp-content/uploads/2013/03/primate-clade-tree.jpg IB BIO 5.4 13 Skills S1: Analysis of cladograms to deduce evolutionary relationships. The pattern of branching in cladograms is assumed to match evolutionary origins of each species. Therefore the sequence of splits at nodes should mirror that of ancestral divergance.
https://sites.google.com/a/canacad.ac.jp/sl-hl-1-biology-4-ferguson/_/rsrc/1403598223535/unit-11-ecology/5-4-cladistics/primate%20cladogram.jpg IB BIO 5.4 14 Skills S1: Analysis of cladograms to deduce evolutionary relationships. The use of molecular clocks can also enhance the information shown in a cladogram by giving an approximate timeline. Species separated by few nodes diverged later and so are more related. Species separated by many nodes diverged further apart and so are less related.
5.4 C - Reclassification
http://group4cladistics.weebly.com/uploads/5/3/1/7/53179435/119029908.jpeg IB BIO 5.4 16 U4: Traits can be analogous or homologous. Structural similarities between organisms can be one of two types: Analagous Unrelated organisms evolved similar structures to fulfill a common need. This is also known as convergent evolution. Analogous Structures Homologous Structures Homologous Similarities are due to common ancestry
https://thegenomestale.files.wordpress.com/2012/05/f1-large.jpg IB BIO 5.4 17 U4: Traits can be analogous or homologous. Problems distinguishing between the types of structures have sometimes led to mistakes in classification. So, DNA and amino acid sequences are now used over morphology. Analogous Structures Homologous Structures
http://biology-forums.com/gallery/18099_27_04_12_2_21_45.jpeg IB BIO 5.4 18 U6: Evidence from cladistics has shown that classifications of some groups based on structure did not correspond with the evolutionary origins of a group or species. Reclassifcation The recent development of sequencing technologies have allowed taxonomists to correctly construct cladograms. When clades based on morphology are incorrect, the species can be reclassified.
http://www.hopspress.com/books/images/scrophulariaceae.jpg IB BIO 5.4 19 Applications A2: Reclassification of the figwort family using evidence from cladistics. The figwort family is an example of reclassification. It was originally the 8 th largest family of angiosperm and included 16 genera. Using cladistics, taxonomists studied the chloroplast DNA sequence of the family. Figwort They discovered that five clades had accidentally been combined into one family. So, a major reclassification was carried out.
http://www.hopspress.com/books/images/scrophulariaceae.jpg IB BIO 5.4 20 As a result of reclassification: Applications A2: Reclassification of the figwort family using evidence from cladistics. 2 families were merged 50 genera moved to plantain family 12 genera moved to boomrape family 13 genera moved to a newly created family Figwort 2 genera moved to anoter new family Figworts were originally the 8 th largest angiosperm family, but now is the 36 th largest.
REVIEW IB BIO 5.4 1. Define cladistics, clade & cladogram. 21 2. Outline evidences that can be used to determine whether species are members of the same clade. 3. Describe the use of DNA as a molecular clock. 4. Compare homologous and analagous structures. 5. Outline the role of structures from #4 in classification. 6. Describe the need for reclassification using Figworts as an example.