Diploid Cells and Reproduction

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. Each chromosome pair is considered to be one set of homologous chromosomes. A single chromosome set consists of two chromosomes, one of which is donated from each parent. In humans, the male sex chromosomes are the X and Y homologues and the female sex chromosomes are the X and X homologues.

The somatic cells in your body are diploid cells.

Somatic cells include all of the cell types of the body, with the exception of 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.

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