(Note: text marked with  was omitted for primary students).
I’m going to talk about us - how we grew from a tiny dot. And about why do we all look different from each other. And why we all look like people, and not a cat or a tree.
(show image of DNA on overhead)
This stuff is the answer to all of these questions: DNA is the most amazing thing. You might have seen pictures of it before. There is DNA in every cell of our body - it is a spiral molecule. And it is the instructions to make our body. This is a billion times bigger than real DNA.
We all started as a tiny single cell. The DNA in that cell has instructions to tell the cell to [divide into more cells, and the instructions to tell those cells which to become back which to become front, then where to make a head, where to make a heart or an eye. Gradually, as more and more instructions are read, a human body] grows and develops into you.
(Show a petri dish of my DNA on overhead)
This is my DNA. I got from the cheek cells in my mouth. In that DNA is the instructions to make my body - my eye colour, my hair colour, why I need to wear glasses, even some of my personality. Your DNA looks the same on the outside, but when scientists look up close they see small differences between different peoples’ DNA. Those tiny differences are what make us all look different.
(Show image of DNA again and point out letters)
(Show hefty book of Shakespere)
If a book is the DNA instructions for a person, we need 100 of these books. Tiny parts of DNA are different between us, like spelling changes in words. That is why we look different. Most of our DNA instructions are the same, as we are all people, but those tiny changes are what makes us all look different.
A few of you have a change in your DNA that none of the rest of us have. Who here has red hair? I can show you exactly what change in the DNA makes your hair this colour - scientists have figured this out.
(Show sequence with one letter change in hair colour gene).
This is a part of a page in our book of DNA instructions. Can you find the one letter that is written in red? The rest of us have a G here. The redheads have a C here. This change in the instructions changes the colour of hair.
Theo has a change in his DNA that none of the rest of us has. Theo has a change to the instructions that tells the body how to grow. This change means that Theo is growing more slowly than the rest of us. Other people with the same DNA change as Theo also grow slowly and look like him. Only one in 10,000 people have the same DNA change as Theo.
Who has blue eyes? Another part of the DNA instruction book determines eye colour. You all have the same DNA letters in that part of the instructions and the rest of us have different instructions.
The only people that have the exact same DNA instructions are identical twins. Any identical twins here?
Everything about the way we look - our hair colour, how we develop, our eye colour, our height, also how we move, see, hear, eat, and talk is built from our DNA instructions. We are so complicated, that we can even think about ourselves thinking. It is absolutely mind boggling how complicated we are - and much of that complexity is built up from the instructions in our DNA. Life comes from this amazing molecule, DNA.
I've talked about our bodies and how we look like we do, but it's only part of the story. Now Theo's Dad will continue the story.