Cells are the basic unit of life. Human body consists of thousands type of cells and each cell has a specific function to perform. The cells can be divided basically into two types based on the presence of chromosome number: Diploid cells (Greek, meaning- ‘double number’) and Haploid cells (Greek, meaning- ‘half’). The number of complete chromosomal set is called ploidy in a biological cell. Tetraploidy (four set of chromosomes) may be seen in certain plants, amphibians, reptiles and insect species. Diploid and haploid cells are entailed in sexual reproduction of higher eukaryotic organisms. Here you can get information related to the diploid and haploid cells.
Humans are diploid organisms with two sets of homologous chromosomes. However, humans also contain haploid sex cells with one set and half the number. Mitosis takes place in diploid cells and haploid cells are formed after meiosis. In men, sperms are the gametic cells produced after spermatogenesis. While in women, ova are the gametic cells produced after oogenesis.
Haploid cells are the cells which contain one complete set of chromosomes that is, 23 chromosomes. In humans and other mammals, the haploid cells are mostly the sex cells (egg and sperms) formed by a process called meiosis. Yeast and fungi are permanently haploid. Also, some organisms like male bees, wasps and ants are haploid organisms.
In the cell nucleus, the haploid number is the number of chromosomes composed of one complete chromosomal set. The chromosome number is usually abbreviated as n, where n describes the number of chromosomes. Different organisms bear different haploid number. The haploid number is articulated in humans as n=23.
Haploid human cells have 1 set of 23 chromosomes:
- Autosomal chromosomes (non-sex chromosomes): 22 sets.
- Sex chromosomes: 1 set.
Ploidy & Meiosis:
Gametes are formed in sexually reproducing organisms by another method of cell division called meiosis. Meiosis is much more complex than mitosis as it involves two divisions of genetic material. In eukaryotic cells, a cell divides into two halves and gives rise to two daughter cells as the life cycle of a cell that involves sexual reproduction. This helps in combination of genes of the parents, without raising the number of chromosomes. During meiosis, the nucleus of the cell divides twice and forms four daughter cells. Meiosis takes place in diploid organisms by formation of gametes (sperm and egg). These gametes are haploid cells that have only one set of chromosomes.
Diploid cells contain two homologous copies of each chromosome donated from the mother and father. With the exception of a few species, all mammals are diploid organisms. During the process of reproduction, haploid cells from the mother and father fertilize to form a diploid zygote that undergoes mitosis to create more diploid cells. In human diploid cells, 46 chromosomes are present. The diploid cells are abbreviated by 2n = 2x, where n = number of chromosomes and x = monoploid number.
Diploid human cells have 2 sets of 23 chromosomes for a total of 46 chromosomes:
- Autosomal chromosomes (non-sex chromosomes): 22 sets of 2.
- Sex chromosomes: 1 set of 2.
Ploidy & Mitosis:
Mitosis is a cell division in which the 'daughter cells' are genetic copies of the 'parent cell'. This cell multiplication lets for replacement of old cells, tissue repair, growth and development.
A ‘parent cell’ must first duplicate (replicate) its genetic material (DNA) in order to divide and generate identical ‘daughter cells’. So, before cell division, somatic diplod cells contain duplicated chromosomes. After cell division, each new cell has a complete diploid number of 46, unduplicated chromosomes.
Human Life Cycle: Haploid to Diploid:
During fertilization, the haploid sperm and egg combines and carries the chromosome count back to 2n diploid number essential for a zygote to have complete genetic information; 2 sets of genetic instructions in 23 pairs of chromosomes.
Diploid Haploid Cells video from youtube:
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