Download DNA, Genes, and Chromosomes

DNA, Genes, and Chromosomes
Explore piece from Science Education Foundation General Atomics
Modified by: Kirstin Bittel and Rachel Hughes
Time :
Preparation Time :
Materials :
1 class period
5 minutes copying lab protocol for each group
5-10 minutes setting up materials
One spool of thread for each class.
DNA, Genes, Chromosomes Overhead
Abstract
During this lesson students will review the structure and function of DNA, genes, and
chromosomes.
Students are engaged by a demonstration illustrating the relative size of DNA, genes and
chromosomes.
Keywords
DNA, genes, chromosome, model,
Objectives
Students will be able to:1. Describe through analogy and model the structure and function of DNA, genes, and
chromosomes.
National Science Education Standard:
Content Area C – The Molecular Basis of Heredity
 In all organisms, the instructions for specifying the characteristics of the organism are
carried in DNA, a large polymer formed from subunits of four kinds (A, G, C, and T). The
chemical and structural properties of DNA explain how the genetic information that
underlies heredity is both encoded in genes (as a string of molecular "letters") and
replicated (by a templating mechanism). Each DNA molecule in a cell forms a single
chromosome. [See Content Standard B (grades 9-12)]
Teacher Background
Related and Resource Websites
www.sci-ed-ga.org/modules/dna/anals/genedna.html
http://www.gm.govt.nz/images/dna.gif
http://www.harcourtschool.com/glossary/science/images/gr6/genes6.jpg
http://www.medceu.com/images/molecularmachine.jpg
Activity:
Engagement (What exactly is DNA?)
1. “Yesterday we extracted DNA from Kiwifruits. What did that DNA looks?” (pause for students
answers) “We know from our study of the cell that there are many organelles in cells. We also
know that we extracted DNA from kiwi cells. That leaves us with the questions…just what is in
those cells and what does it do?”
2. Show students the spool of thread and ask them to describe what substances (wood and
cotton) and structures (spool and thread) they see. As students describe the thread being wound
around the spools, ask them to make an analogy between the thread and spool and what they did
yesterday. What is the thread (DNA)? What is the spool (proteins that hold DNA together)?
3. After students are able to use the models being easily, unwind a good bit of the thread, until it
begins to accumulate in your hand, and try to throw it to one of the students. Of course, it doesn’t
make it. Ask students what would be a better way to transfer the DNA from one place to another
(roll it back up on the spool)? What does the thread wrapped around the spool represent (a
chromosome)? Stress that when DNA is being transferred (like during mitosis and DNA
replication) it must be “wound up,” but when it is being used (during interphase) it is no longer
wound up.
3. Uncoil about 2 feet of thread and color it red. What do students think this represents (a
nucleotide sequence for a gene – perhaps a gene for a red pigment)? Color another 2-foot
segment blue. This might represent a gene for a blue pigment. Recoil the thread so that the red
and blue appear in the linear order of the thread. This will illustrate to students how genes
appear stacked on chromosomes.
4. Review with students what each material was used to represent the DNA, genes, and
chromosomes (thread, colored sections of thread, and thread on spool).
5. Take time now to show students real models of DNA and chromosomes. Take time to discuss
the shape of each piece. You may use Overhead 1 or any other overheads or illustrations
available to you. Other excellent examples can be found at …
http://www.harcourtschool.com/glossary/science/images/gr6/genes6.jpg
http://www.medceu.com/images/molecularmachine.jpg
This clearly illustrates that genes are long segments of DNA and are located on chromosomes.
Ask students to come up with their own analogy for DNA, genes and chromosomes. Give them
the Matt Ridley (author of Genome) example: the genome is like a book. The chromosomes are
like chapters in that book. The genes are like the words and paragraphs that are in each chapter.
The DNA bases are like the letters used to write those words.
This is an excellent opportunity to assess prior knowledge.
Have students record concluding thoughts in their science notebooks.