||1 class period
coping lab protocol for each group
5-10 minutes setting up materials
||One spool of thread for each class.
DNA, Genes, Chromosomes Overhead
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.
DNA, genes, chromosome, model,
Students will be able to:
1. Describe through analogy and model the structure
and function of DNA, genes, and chromosomes.
National Science Education Standards
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)]
Related and Resource Websites
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.
4. 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
5. Review with students what each material was used to represent the DNA, genes,
and chromosomes (thread, colored sections of thread, and thread on spool).
6. 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 …
This clearly illustrates that genes are long segments of DNA and are located
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.