The Same Set in Every Cell
You are an organism. You have cells, your cells have
nuclei, and the nuclei contain chromosomes. So if we're
going to think about chromosomes, we might as well start
by thinking about you and your chromosomes.
You are made up of billions and billions of cells.
Every non-sex, or somatic, cell has 46 chromosomes
sitting in its nucleus. Sex cells are sperm and ova.
They are special.
Here's the important point: the
46 chromosomes that are sitting in any one of your somatic
cells are identical to the 46 that are sitting in every
other of your somatic cells.
It's not like your
skin cells have one set of chromosomes and your kidney
cells have another. All of your cells have exactly the
same set of chromosomes in their nuclei.
The same is true of every other organism in the whole
world. Think about your best friend. His (or her) chromosomes
are different from yours, that's for sure. But the 46
chromosomes in any one of his cells is absolutely identical
to the 46 chromosomes that are in every other one of
Think about your dog, cat, turtle, or hamster.
Think about some tree on your block. Think about any
organism you like, and this will always be true; within
any organism, the chromosomes that are sitting in one
cell's nucleus are identical to the set that's sitting
in every other cell's nucleus.
Within any individual, all cells have identical chromosomes.
That's true. Two different individuals do not have the
same sets of chromosomes. That's almost always true.
The exception is: identical twins. Each identical twin
has exactly the same chromosomes as the other.