Inside a living cell (plant and animal) is a nucleus which contains chromosomes.
There are 46 chromosomes in human body cells, spread out randomly within the nucleus.
Lined up in order of size, these chromosomes look like this although chromosome 46 changes depending on whether the cell is from a female or a male.
You will notice that every second chromosome is similar. The pairs carry the same type of genes along their length. Within each pair you inherit one chromosome from your mother and one from your father.
If this cell was from a male, 45 would be called X chromosome and 46 would be called a Y chromosome.
If this cell was from a female, 45 would be called X chromosome and 46 would be called X chromosome.