The number of complete sets of chromosomes is called ploidy in a biological cell. Somatic cells or non-sex cells in humans contain two sets of chromosomes, one set inherited from each parent, and thus called the diploid number of chromosomes. The gametes or sex cells (egg and sperms) contain one set of chromosomes, and are called haploid number of chromosomes.
What is Haploid Number?
This number of an organism is represented by 1n. The number of chromosome pairs is not limited in a cell. Haploid animals are very rare, as most organisms have diploid cells. It is defined as a cell having only a single set of chromosomes. Haploid organisms do not have multiple copies of genes that are required to program the same information. All mammals have their reproductive cells with this number of chromosomes. The sperms and eggs have haploid number of chromosomes, as after fertilization, the zygote formed will be diploid number.
The gametes or sex cells are formed by a different method of cell division, other than mitosis. This method is called meiosis, and is much more complex than mitosis. In mitosis, there is duplication and division of chromosomes. Meiosis involves two divisions of genetic material, that gives rise to diploid number of cells.
The gametes have half the number of chromosomes than the initial cells from where they are produced. These haploid cells are formed from specialized reproductive tissues called gonads. The female gonads (ovaries) and the male gonads (testes) are the sites where meiosis takes place.
What is the Number for a Human?
The haploid sperm and egg fertilize and bring the chromosome count to 2n diploid number. This is necessary for the formation of zygote, that contains complete sets of chromosomes. This complete genetic chromosome set contains the much-needed genetic information for making a human. The haploid chromosome number in humans is 23. This brings the diploid chromosome number in humans to 46.
The haploid chromosome number in humans is 1 set of 23 chromosomes. Of these, the autosomal chromosomes (non-sex chromosomes) contain 22 sets, and sex chromosomes have 1 set.