You already learned that DNA is like a big instruction book inside your body. It tells your body what to do.
But not every word in that book gives orders. Some parts are quiet. Some are just for holding pages together.
So where are the parts that give real, working instructions?
That’s what we’ll learn today.
🧠 What Is a Gene?
A gene is one tiny part of your DNA that gives your body a job to do.
Think of DNA as a very big string. A gene is a small section of that string.
It’s the part that matters most — the part your body reads to build things like:
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Your skin
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Your blood
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Your hair
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Even your smile
Every gene is like a sentence that says:
“Hey body, build this now!”
📚 Genes Are Sentences in the DNA Book
DNA is full of letters: A, T, C, and G.
The order of these letters is super important. When they are in the right order, they make a gene.
That gene tells your body how to make something very special:
A protein.
Proteins are the tiny machines that build your body and help it work.
We’ll talk more about proteins in the next lesson, but for now, just remember:
A gene is a recipe. It tells your body how to make one protein.
🧩 Not All DNA Is a Gene
Your DNA is super long — billions of letters long!
But guess what? Only a tiny bit of that is made of genes.
Most of your DNA is not used to make proteins. It just sits quietly.
Some parts help the genes turn on and off.
Some parts are still a mystery to scientists.
So:
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Some DNA = genes (the recipes)
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Most DNA = not genes (extra pages, spaces, bookmarks)
🧬 Every Gene Has Three Parts
Just like a sentence starts and ends, genes have special parts too:
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Start → “Begin here!”
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Middle → The real instructions
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Stop → “You’re done!”
Your body only reads from the start to the stop.
📖 Do All Cells Use All Genes?
Nope! Even though every cell has all your genes, each cell only reads the genes it needs.
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A skin cell reads skin genes.
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A heart cell reads heart genes.
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A brain cell reads brain genes.
This is called gene expression — a fancy way of saying “only the right gene gets used at the right time.”
Your cells are smart like that.
🎛️ Genes Can Turn On and Off
Genes don’t work all the time.
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Some genes are always on (like the ones that help you breathe).
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Some genes are only on when you grow.
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Some genes are turned off and never used.
Your body has helpers that flip the switch — on or off — just like a light.
⚠️ What If a Gene Is Wrong?
Sometimes a gene has a tiny mistake. Maybe one letter is missing or in the wrong spot.
This is called a mutation.
Some mutations are bad. Some are good. Some don’t do anything at all.
But here’s a fun fact:
Mutations are how living things change over time.
They help us grow new traits like:
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Curly hair
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Fast legs
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Better eyesight
This is how animals and people slowly evolve.
🧠 Let’s Review!
✅ A gene is a small part of DNA
✅ It gives your body the recipe to make one protein
✅ Not all DNA is a gene — most is quiet
✅ Cells only read the genes they need
✅ Genes can turn on or off like a light switch
✅ Mistakes in genes are called mutations — they can help, hurt, or do nothing