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Students need to complete Visualizing Codon Expansions (Part A) prior to beginning this activity.

 Background: 

The change in genes over time in the arena of natural selection is the driving force of evolution. Some genes are highly conserved and show low rates of change. On the other end of the spectrum some genes are highly variable and may lead to more rapid rates of evolutionary change. One of the goals of evolutionary biologists is to reconstruct "family" histories, DNA is one tool that is used to accomplish this task.

This lab activity continues from Visualizing Codon Expansions and compares phenograms (visual representation of relatedness) using two different types of gene regions in Drosophila. The glass gene is variable between species (some species have many repeats, some have none). A second gene, the "sia" gene is considered highly conserved. This will serve as a basis for comparison. From the data, students will make comparisons of two gene trees and gain an understanding of the importance of using many pieces of evidence to construct the evolutionary past. 

Objectives:

1. To compare a highly conserved gene region to a rapidly evolving region

2. To create a gene phenogram using DNA sequences

3. Introduce students to bioinformatics using computer data bases

Materials:

1. Computer with Internet access

2. Sequence data in digital format (Word or Text document)

3. Printed Direction Sheet

 Procedure:

PART C -

 Print this page before beginning the activity, but do not close it to maintain the hot links.

Importing the DNA Sequences:

1.Open your Internet Browser and go to Dolan DNA Learning Center

2. Enter DNA sequences for all fly species and both gene regions using the procedure in Part A.

3. When all data has been entered you will have a total of 10 sequences.

4. Select all the flies of your assigned gene region.

5. Then select phylogenetic tree from the pulldown menu to the right of COMPARE.

6. Select COMPARE.

7. In the pop-up window select phenogram from the pulldown menu.

8. SKETCH your resulting tree.

Questions:

1.Compare and contrast the phenograms for each gene region.

2. If another highly conserved gene region was analyzed what do you think that phenogram would look like relative to the glass and sia gene?

3. What other information do scientists use to construct evolutionary relationships?

4. Highly variable regions are considered hot spots in your genome. Why would some gene regions be more conserved than others?

5. Scientists have reported that codon repeats in genes associated with human disease are also found in non-human primates. These repeats are smaller and less harmful. How can animal models aid in an understanding of the evolution of human disorders?

References:

Djian, P. et.al. Codon repeats in genes associated with human diseases: Fewer repeats in the genes of nonhuman primates and nucleotide substitutions concentrated at the sites of reiteration. Proc. Natl. Acad. Sci. USA. vol. 93. pp. 417-421.

Zilversmit (2002) unpublished data

Standards:

National Benchmarks

Resources: 

The Dolan Learning Center. www.dnalc.org/