Human boy cells each contain 23 pairs of chromosomes. Parents pass on their genes in their sex cells (ovum in females, sperm in males). Each sex cell contains 23 separate chromosomes which, when they join in fertilisation, creates 23 pairs of chromosomes - a new being with brand new cells. Each pair of chromosomes carries the same genes in the same places.
Which chromosome we get from each pair of our parents' chromosomes is completely random. This is why we look a little bit like our parents and our siblings, but we are not identical to them.
Females have ** chromosomes - all X
Males have XY chromosomes
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