Why do your siblings have different DNA to you?
Maybe your siblings are adopted.
Or maybe YOU’RE adopted.
Anything is possible.
But the other day I got the news that I’m not adopted, and neither is my sister, Carla.
Which got me thinking, how is it that Carla and I came from the exact same two sets of DNA, and yet somehow ended up SO FRIGGIN DIFFERENT?
Turns out this genetic variation is due to a science biology thing called MEIOSIS. Pronounced, MY - O - SIS - as in
So: all cells in a person contain the same complete sets of DNA.
That DNA looks like this: chromosome pairs (squiggly lines below), made up of lots of genes (little colourful blobs - not actually blobs IRL).
Usually there are 23 pairs but I only drew 4 because lazy.
One half of each chromosome pair comes from each parent.
Each pair of chromosomes has a few specific gene jobs - for example, this little section of this particular chromosome pair (below) is where the genes are for deciding hair colour,
And the genes from the opposing chromosomes in a pair might have a few different ideas about what the final hair colour should actually be.
The way it’s finally decided depends a lot on which gene ends up being more dominant about their opinion -
And those different gene interactions/combinations give us all our unique traits. Like drawing ability.
So the only thing that can explain my sister being different from me is if my mom and dad each gave us a different combination of chromosomes. But how is that possible, given that they each only have one set of DNA?
It all has to do with the special way egg and sperm cells are made.
When a regular cell wants to make more of itself, it simply duplicates its chromosomes, splits in half and ba-boom: two new identical cells.
But when a cell wants to make a sperm or egg cell, the process is a whole other thing. It also starts off by making duplicates of its chromosome pairs, but then those chromosome pairs kind of lie on top of each other and scramble up and end up swapping a whole lot of gene blobs.
So then when the cell then divides in half (each half taking one half of the duplicated chromosomes), the new cells aren’t the same as each other OR the same as their parent cell.
Then THESE cells split in half again, each one making two cells that have just 23 single chromosome strands. These cells are egg cells or sperm cells (called gametes.)
When one of these egg/sperm cells GAmeets another one (heh heh), they combine to make a baby cell with a TOTALLY NEW SET OF DNA HOW COOL IS THAT!!!!
And that new cell duplicates a ton of times to become a baby.
And that’s why my sister draws nicer than me.
Alastair the scientist who suggested this topic!
my real parents
Thanks for reading! Do you have a question that you would like answered with comics? Reply to this mail or leave them in the comments!