Investigation: Comparing DNA Sequences to Understand Evolutionary Relationships with BLAST

Name______

Investigation: Comparing DNA Sequences to Understand Evolutionary Relationships with BLAST Using bioinformatics as a tool to determine evolutionary relationships.

Between 1990–2003, scientists working on an international research project known as the Human Genome Project were able to identify and map the 20,000–25,000 genes that define a human being. The project also successfully mapped the genomes of other species, including the fruit fly, mouse, and Escherichia coli. The location and complete sequence of the genes in each of these species are available for anyone in the world to access via the Internet.

Why is this information important? Being able to identify the precise location and sequence of human genes will allow us to better understand genetic diseases. In addition, learning about the sequence of genes in other species helps us understand evolutionary relationships among organisms. Many of our genes are identical or similar to those found in other species.

Suppose you identify a single gene that is responsible for a particular disease in fruit flies. Is that same gene found in humans? Does it cause a similar disease? It would take you nearly 10 years to read through the entire human genome to try to locate the same sequence of bases as that in fruit flies. This definitely isn’t practical, so a sophisticated technological method is needed.

Bioinformatics is a field that combines statistics, mathematical modeling, and computer science to analyze biological data. Using bioinformatics methods, entire genomes can be quickly compared in order to detect genetic similarities and differences. An extremely powerful bioinformatics tool is BLAST, which stands for Basic Local Alignment Search Tool. Using BLAST, you can input a gene sequence of interest and search entire genomic libraries for identical or similar sequences in a matter of seconds.

In this laboratory investigation, you will use BLAST to compare several genes, and then use the information to construct a cladogram. A cladogram (also called a phylogenetic tree) is a visualization of the evolutionary relatedness of species. A cladogram is treelike, with the endpoints of each branch representing a specific species. The closer two species are located to each other, the more recently they share a common ancestor.

Cladrograms can also include additional details, such as the evolution of particular physical structures called shared derived characters. The placement of the derived characters corresponds to when (in a general, not a specific, sense) that character evolved; every species above the character label possesses that structure. Historically, only physical structures were used to create cladograms; however, modern-day cladistics relies heavily on genetic evidence as well. For example, chimpanzees and humans share 95%+ of their DNA, which would place them closely together on a cladogram. Humans and fruit flies share approximately 60% of their DNA, which would place them farther apart on a cladogram.

PRE-LAB: 1) Use the following data to construct a cladogram of the major plant groups (“1” = characteristic is present within group):

Organisms Vascular Tissue Flowers Seeds Mosses 0 0 0 Pine trees 1 0 1 Flowering plants 1 1 1 Ferns 1 0 0

2) GAPDH (glyceraldehyde 3-phosphate dehydrogenase) is an enzyme that catalyzes the sixth step in glycolysis, an important reaction that produces molecules used in cellular respiration. The following data table shows the percentage similarity of this gene and the protein it expresses in humans versus other species. For example, according to the table, the GAPDH gene in chimpanzees is 99.6% identical to the gene found in humans, while the protein is identical.

Species Gene Percentage Similarity Protein Percentage Similarity Chimpanzee (Pan troglodytes) 99.6% 100% Dog (Canis lupus familiaris) 91.3% 95.2% Fruit fly (Drosophila melanogaster) 72.4% 76.7% Roundworm (Caenorhabditis elegans) 68.2% 74.3% a) Why is the percentage similarity in the gene always lower than the percentage similarity in the protein for each species? (Hint: Recall how a gene is expressed to produce a protein.)

b) Draw a cladogram depicting the evolutionary relationships among all five species (including humans) according to their percentage similarity in the GAPDH gene.

PROCEDURE (Part One): Step 1: Make a hypothesis as to where you believe the fossil specimen should be placed on the cladogram based on the morphological observations that you made of the fossil. Mark (and label) your hypothesis on the cladogram above.

OBSERVATIONS: ______

Step 2: Download the sequences of the four gene samples taken from the unknown fossil. These can be found on my website under the ‘Labs & Lab Notebook’ link. Step 3: Use the following website for your genetic analysis— BLAST – use this website to compare gene sequences with genomic DNA from representative organism in a data base. http://blast.ncbi.nlm.nih.gov/Blast.cgi

Step 4: Go to the BLAST website. Click on the green rectangle labeled ‘nucleotide blast.’ Copy-and- paste the gene sequence for FOSSIL GENE 1 into the ‘Enter Query Sequence’ box on the BLAST webpage. Under ‘Choose Search Set- database,’ make sure that “others (nr etc.)” is selected. Under ‘Program Selection,’ make sure that “Highly similar sequences (megablast)” is selected.  Then, click the blue “BLAST” button to search for gene sequences in different species that are similar to the unknown fossil gene sequence.

Step 5: When the results of the BLAST sequence comparison appear, scroll down to the section entitled ‘sequences producing significant alignments.’ The species in the list that appears below this section are those with sequences identical to (or most similar to) the gene of interest. The most similar sequences are listed first.  You’ll need to click on the particular species listed and the ‘accession’ link, where you’ll find more info that includes the common name of the species, the # of nucleotides that match between the gene of interest and the known organism, etc. Using the information from your results, complete TABLE 1. REPEAT STEPS 4 & 5 FOR ALL FOUR FOSSIL GENES. TABLE 1

Fossil Most closely related Most closely related “Max Number of % nucleotide match Next TWO most Gene organism (genus and species (common Score” matching (“Max Identity”) closely related # species name) name) nucleotides organisms (fossil gene (common vs. organism names only) gene)

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Step 6: Based on what you’ve learned from the sequence analysis and what you know from the fossil structure itself, decide where the new fossil species belongs on the cladogram. Mark (and label) your results on the cladogram so that you may compare your results w/ your hypothesis. PROCEDURE (Part Two): Now that you’ve completed Part One of the investigation, you should feel more comfortable using BLAST. The next step is to learn how to find and BLAST your own genes of interest. To locate a gene, you will go to the following website: NCBI Gene – use this website to obtain gene sequences for analysis. http://www.ncbi.nlm.nih.gov/gene

Step 1: Use the search tool at the top of this website to search for the sequences listed in TABLE 2.

Step 2: Click on the first link that appears and scroll down to the “NCBI Reference Sequences.” Under “mRNA and Proteins,” click on the first file name. It will be named “NM_000257.2” or something similar.

Step 3: Just below the gene title, click on “FASTA.” This is the name for a particular format for displaying sequences.

Step 4: Copy the entire gene sequence, and then go to the BLAST website (see Procedure: Part One, Step 3.)

Step 5: Under ‘Basic BLAST’, click on ‘nucleotide blast.’ Paste your gene sequence into the ‘Enter Query Sequence’ box on the BLAST webpage. Under ‘Choose Search Set,’ make sure that “others (nr etc.)” is selected. Under ‘Program Selection,’ make sure that “Highly similar sequences (megablast)” is selected.

Then, click the blue “BLAST” button to search for gene sequences in different species that are similar to the human gene sequence of interest.

Step 6: When the results of the BLAST sequence comparison appear, scroll down to the section entitled ‘sequences producing significant alignments.’ The species in the list that appears below this section are those with sequences identical to (or most similar to) the human gene of interest. The most similar sequences are listed first, as the higher “max score” usually indicates closer genetic relationships.

***For TABLE 2, exclude all Homo sapiens (human) DNA sequence matches. Choose the DNA sequence from the organism other than Homo sapiens within your BLAST results list that most closely matches the sequence of your human gene of interest. For example, Pan troglodytes is the scientific name of the common chimpanzee, where Pan is the genus name and troglodytes is the species name.***

Remember to click on the particular species listed and the ‘accession’ link, where you’ll find more info that includes the common name of the species, the # of nucleotides that match between the gene of interest and the known organism, etc. Using the information from your results, complete TABLE 2. REPEAT STEPS 1-6 FOR ALL FOUR PROVIDED HUMAN GENES OF INTEREST.

Step 7: Think of a human protein NOT listed in the table, search for the gene sequence of this protein, run a BLAST comparison for this protein, and list all results in the final row of TABLE 2.

TABLE 2

Human Most closely related Most closely “Max Number of % nucleotide match Next TWO most Gene organism (genus and related species Score” matching (“Max Identity”) closely related species name) (common name) nucleotides organisms (human gene (common vs. organism names only) gene) Human Estrogen / Receptor

Human Keratin 18 /

Human Catalase /

Human Myosin 7 / (cardiac)

Human ______/ ______Analysis 1) Using your results from TABLE 2, sketch a hypothetical cladogram based upon gene sequence matches. Your cladogram should include humans and ALL animals listed within TABLE 2.

2) What is the function in humans of each of the proteins produced from the genes in TABLE 2? GENE PROTEIN FUNCTION Human Estrogen Receptor

Human Keratin 18

Human Catalase

Human Myosin 7 (cardiac)

Human ______3) Is it possible to find the same gene in two different kinds of organisms but not find the protein that is produced by that gene in both organisms? Why or why not?

4) If you found the same gene in all organisms you test, what does this suggest about the evolution of this gene in the history of life on earth?

5) Does the use of DNA sequences in the study of evolutionary relationships mean that other characteristics are unimportant in such studies? Explain your answer.