👶 You Started as a Single Cell
Before you were born, you were just one tiny dot.
That dot was called a cell — and it was the very first part of you.
Inside that tiny cell was something HUGE (not in size, but in power):
👉 Your DNA — with all your genes.
Those genes would go on to tell your body:
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How to grow arms and legs
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What color your eyes should be
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How tall you might become
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And much, much more
But where did that DNA come from?
Let’s find out.
🧬 You Get Half from Mom, Half from Dad
Your genes didn’t just appear by magic.
They came from your parents.
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Your mom gave you half of your DNA.
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Your dad gave you the other half.
When their cells came together to make you, they each gave you 23 chromosomes.
So now you have 46 chromosomes — 23 from each parent.
And inside those chromosomes?
All your genes.
🧫 The Cell That Made You Had to Copy DNA First
Here’s the wild part:
Before your body could grow — even before your cells could divide into more cells — your DNA had to be copied.
It had to make a perfect copy of itself for every new cell.
Why?
Because every new cell in your body needs a full set of your genes to know what to do.
No genes = no instructions = no body.
🧠 How Does DNA Get Copied?
Let’s imagine DNA like a twisty ladder made of letters — A, T, C, G.
Here’s how copying works:
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The ladder unzips down the middle.
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Each side gets a new matching half.
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A always pairs with T
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C always pairs with G
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Now, you have two full ladders, both the same.
This is called DNA replication — the fancy word for copying DNA.
🛠️ Special Proteins Help with Copying
Copying DNA is a big job.
It has to be done very carefully — one mistake could change the entire body.
So your body uses helper proteins (called enzymes) to:
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Unzip the DNA
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Match the letters
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Fix any mistakes
Think of them as super-fast builders, using rules to make perfect copies of the original code.
🧬 Every Time a Cell Divides, It Copies the Genes
You started as 1 cell. Now you’re made of trillions of them.
How did that happen?
Each time one of your cells wanted to divide (split into two), it had to:
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Copy all your DNA
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Split into two cells
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Send one full set of genes into each new cell
So every cell has the same DNA — your full group of genes — just like the first one!
Quick Reminder: Group of genes are called genomes, in case you forgot!
🧪 But Copying Isn’t Always Perfect…
Even though your body tries really hard to copy DNA exactly, sometimes…
👉 A letter gets missed
👉 A letter gets changed
👉 An extra letter gets added
This is called a mutation.
We’ve talked about this before — mutations can be:
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Bad
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Good
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Or not matter at all
Most of the time, they get fixed right away. But sometimes, the mutation stays.
👶 How Babies Get Genes
When a baby is made, two special cells meet:
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One from the mom (egg cell)
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One from the dad (sperm cell)
Each of these cells has only 23 chromosomes — half the usual number.
When they join together, they make a brand-new cell with:
✅ 46 chromosomes
✅ A brand-new mix of genes
✅ A unique code that’s never been seen before
That cell is the start of a new person — you!
🔁 Genes Pass Down Over Time
Your genes came from your parents.
Theirs came from their parents.
And so on… going back for millions of years.
Some of your genes were passed down from:
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Your great-grandparents
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Ancient humans
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Even earlier living things
That means your body carries tiny pieces of ancient life, hidden in your DNA.
Isn’t that amazing?
🧠 Recap!
✅ You get half your genes from mom, half from dad
✅ DNA has to copy itself before your body can grow
✅ Copying uses special rules and helper proteins
✅ Every new cell in your body gets a full set of genes
✅ Copying isn’t always perfect — that’s how mutations happen
✅ Each baby starts as one cell with a brand-new mix of genes
✅ Your genes have been passed down for millions of years