DNA carries the instructions for an organism. It is coiled into chromosomes in the nucleus; a gene is a section of DNA that codes for a protein. Alleles are different versions of the same gene.
Unwound, the DNA in one of your cells would be about two metres long. It fits in a nucleus a hundredth of a millimetre across.
In Year 9 you learnt gametes carry half the chromosomes. This lesson: what a chromosome is made of, and what a gene is.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explore: Try it on the board and compare what happens with your prediction.
Explain: Use the particle model to explain what you saw.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: bigger or smaller?
ExploreTry it on the board and compare what happens with your prediction.
Explore: zoom in
Press Zoom in and read each level before going on.
Try it yourselfYour edits are saved in this browser.
Zoom all the way in from the body to a single gene.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: DNA, genes and alleles
In your book: draw a nested diagram (cell, nucleus, chromosome, DNA, gene) and label an allele.
Match each word to its meaning.
DNA
Chromosome
Gene
Allele
Elaborate TypicalUse the same idea in a new context.
Elaborate: from code to characteristic
Put the steps in order.
A gene's sequence of bases (A, T, C, G) is read
The cell builds a protein from that code
The protein does a job (a pigment, an enzyme, a structure)
A characteristic appears (such as eye colour)
Elaborate WiderUse the same idea in a new context.
Elaborate: the same code everywhere
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Write one sentence: "At first I thought… Now I think… because…"
Revision summary
DNA carries coded instructions as a sequence of bases (A, T, C, G).
A chromosome is one long DNA molecule, coiled; humans have 46, in 23 pairs (one of each pair from each parent).
A gene is a section of DNA coding for a protein; alleles are different versions of one gene.
Genotype: the alleles you have (such as A and O). Phenotype: the characteristic that shows (blood group A).
For teachers
Students relate DNA, chromosomes, genes and alleles by size and meaning, and explain chromosome pairs (AC9S10U01, node 1, a hinge node). About 20 minutes.
I can put the cell, nucleus, chromosome, DNA and gene in order of size.
I can define gene and allele.
I can explain why chromosomes come in pairs.
Before class
A concept tutorial for introducing or revising the idea; it does not replace a DNA extraction practical (strawberries or kiwifruit). Set the width with ?width=minimum, typical (default) or wider.
The hinge misconceptions are confusing gene, chromosome and DNA, and thinking there is a separate gene for each version of a characteristic.
Board notes: the zoom is not to scale; the nucleus shows only some chromosomes; the base sequence shown is illustrative, not a real gene.
Running the lesson
Engage: see how many put gene and DNA in the wrong order.
Explore: ask what the red and blue chromosomes mean at the nucleus level.
Explain: the earlobe question is the checkpoint (gene versus allele).
The hard part (on purpose)
Keeping DNA, gene, chromosome and allele apart by size and job. When the words blur, ask which one is inside which, before naming any of them.
When students get stuck
A student says a chromosome and DNA are different things. Ask: What did you see when you zoomed into the chromosome? Fix: A chromosome is DNA, tightly coiled.
A student says there's a gene for blue eyes and a gene for brown. Ask: Is it the same section of DNA, in a different version? Fix: Yes: one gene, different alleles.
Stretch and support
Stretch: The four bases pair up A with T and C with G. Why might that help a cell copy its DNA?
Support: Give a nested-boxes diagram with the five words to place.
Where it leads
Next: meiosis (node 3) and Punnett squares (node 4).
In class: DNA extraction from strawberries.
What each step is for
Engage: bigger or smaller?: Students who confuse gene, chromosome and DNA can't order them by size; the zoom puts them in order.
Explore: zoom in: Zooming from a person to one gene in six steps shows each structure inside the last.
Explain: DNA, genes and alleles: Separating the gene (the section of DNA) from the allele (a version) and the characteristic is the hinge.
Elaborate: from code to characteristic: Ordering the steps from gene to characteristic answers 'what do genes do?'
Elaborate: the same code everywhere: Recognising that all cells hold the same DNA but use different genes links back to specialised cells.
Now you can
Put the cell, nucleus, chromosome, DNA and gene in order of size.