Here's why:
* Diploid cells: Normal human cells have 46 chromosomes, arranged in 23 pairs (one chromosome from each pair coming from the mother and one from the father). This is called being diploid.
* Meiosis: Gametes are produced through a special type of cell division called meiosis. Meiosis involves two rounds of division, resulting in four daughter cells, each with half the number of chromosomes as the original cell.
* Haploid cells: This means that gametes have 23 chromosomes, one from each pair. They are called haploid.
* Fertilization: When a sperm cell (haploid) fertilizes an egg cell (haploid), the resulting zygote is diploid again, with 23 chromosomes from the father and 23 chromosomes from the mother.
In summary: Human gametes are haploid and have only one chromosome from each pair, not two.