Classifying Animals by Appearance Versus DNA Sequence

Classifying Animals by Appearance Versus DNA Sequence


Megan E. Rokop
Educational Outreach Program Director
Broad Institute of MIT & Harvard
Cambridge, Massachusetts 02139 USA

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The topic of this video module is how to classify animals based on how closely related they are. The main learning objective is that students will learn how to make phylogenetic trees based on both physical characteristics and on DNA sequence. Students will also learn why the objective and quantitative nature of DNA sequencing is preferable when it come to classifying animals based on how closely related they are. Knowledge prerequisites to this lesson include that students have some understanding of what DNA is and that they have a familiarity with the base-pairing rules and with writing a DNA sequence. However, these topics are covered briefly in the lesson. All necessary hand-outs and worksheets are downloadable in Word and PDF formats, and materials needed for the lesson are only paper and pen/pencil. The types of in-class activities for this lesson include creating phylogenetic trees, calculating pair-wise differences of the gene sequences of 10 animals, and group discussions. This learning video also includes a lesson extension for teachers and students with access to a computer and the Internet. (See Teacher Guide segment) This extension introduces teachers to free online software that will allow students to use the program written by scientists to examine the hundreds and thousands of letters of the DNA sequences of mammals, count the pair-wise differences and make phylogenetic trees.

Instructor Biography

Megan Rokop is Director of the Educational Outreach Program at the Broad Institute of MIT & Harvard, a biomedical research institute located on the MIT campus. Megan earned her Ph.D. in biology at MIT, and has taught biology both to high school students in the Boston area, and to undergraduate students at MIT.

Additional Online Resources

The Tree of Life Web Project (ToL) is a collaborative effort of biologists and nature enthusiasts from around the world. On more than 10,000 World Wide Web pages, the project provides information about biodiversity, the characteristics of different groups of organisms, and their evolutionary history (phylogeny).

ClustalW2 is a general purpose multiple sequence alignment program for DNA or proteins. It calculates the best match for the selected sequences, and lines them up so that the identities, similarities and differences can be seen. Evolutionary relationships can be seen via viewing Cladograms or Phylograms.

Entrez is the integrated, text-based search and retrieval system used at the National Center for Biotechnology Information (NCBI) for the major databases related to biotechnology.

The Basic Local Alignment Search Tool (BLAST) finds regions of local similarity between gene sequences. The program compares nucleotide or protein sequences to sequence databases and calculates the statistical significance of matches. BLAST can be used to infer functional and evolutionary relationships between sequences as well as help identify members of gene families.