What Is A Diploid Cell?

Human karyotype
This human karyotype shows the complete set of human chromosomes. Each chromosome pair represents a set of homologous chromosomes in each diploid cell. Credit: somersault18:24/Science Photo Library/Getty Images

A diploid cell is a cell that contains two sets of chromosomes, which is double the haploid chromosome number. Each pair of chromosomes in a diploid cell is considered to be one homologous chromosome set. A single chromosome set consists of two chromosomes, one of which is donated from the mother and the other from the father. Humans have 23 sets of homologous chromosomes. Paired sex chromosomes are the (X and Y) homologues in males and the (X and X) homologues in females.

The somatic cells in your body are diploid cells. Somatic cells include all of the cell types of the body, except for the gametes or sex cells. Gametes are haploid cells. During sexual reproduction, gametes (sperm and egg cells) fuse at fertilization to form a diploid zygote. The zygote develops into a diploid organism.

Diploid Number

The diploid number of a cell is the number of chromosomes in the cell nucleus. This number is commonly abbreviated as 2n, where n stands for the number of chromosomes. For humans, this equation would be 2n=46. Humans 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.

Diploid Cell Reproduction

Diploid cells reproduce by the process of mitosis. In mitosis, a cell makes an identical copy of itself allowing its DNA to be replicated and distributed equally between two daughter cells.

Somatic cells go through the mitotic cell cycle, while gametes are reproduced by meiosis. In the meiotic cell cycle, four daughter cells are produced instead of two. These cells are haploid containing half the number of chromosomes as the original cell.

Polyploid and Aneuploid Cells

The term ploidy refers to the number of chromosome sets found in a cell's nucleus.

Chromosome sets in diploid cells occur in pairs, while haploid cells contain half the number of chromosomes as a diploid cell. A cell that is polyploid has extra sets of homologous chromosomes. The genome in this type of cell contains three or more haploid sets. For example, a cell that is triploid has three haploid chromosome sets and a cell that is tetraploid has four haploid chromosomes sets. A cell that is aneuploid contains an abnormal number of chromosomes. It may have extra or missing chromosomes or may have a chromosome number that is not a multiple of the haploid number. Aneuploidy occurs as a result of chromosome mutation that happens during cell division. Homologous chromosomes fail to separate correctly resulting in daughter cells with either too many or not enough chromosomes.

Diploid and Haploid Life Cycles

Most plant and animal tissues consist of diploid cells. In multicellular animals, organisms are typically diploid for their entire life cycles. Plant multicellular organisms, such as flowering plants, have life cycles that vacillate between periods of a diploid stage and a haploid stage. Known as alternation of generations, this type of life cycle is exhibited in both non-vascular and vascular plants.

In liverworts and mosses, the haploid phase is the primary phase of the life cycle. In flowering plants and conifers, the diploid phase is the primary phase and the haploid phase is totally dependent upon the diploid generation for survival. Other organisms, such as fungi and algae, spend the majority of their life cycles as haploid organisms that reproduce by spores.