By haploid_vs_diploid.svg: Ehamberg derivative work, courtesy of Wikimedia Commons.
Analysis of the DNA content can provide valuable information regarding the status of chromosomes. Ploidy is defined as the number of sets of chromosomes that exist in a cell. A haploid cell contains one complete set of chromosomes. Below are some additional terms that further describe these chromosome sets.
A diploid cell is a cell that contains two sets of chromosomes, or two haploid sets. The normal copy number of the human cell is two copies of each chromosome (autosome) and either two X chromosomes (female) or an X and a Y chromosome (male), for a total of 46 chromosomes.
Aneuploidy is an abnormal number of chromosomes and involves the loss or gain of one or more chromosomes. This can occur during mitosis when chromosomes do not segregate to each daughter cell. This is also known as non-disjunction. In the event that one chromosome does not segregate properly, the result will be one daughter cell with a triploid content for that chromosome and one daughter cell with one copy of that chromosome which is known as monosomy. Non-disjunction occurs frequently in tumor cells as they develop into more and more malignant cells.
Polyploidy is the process of genome doubling that produces multiple sets of chromosomes. The gain of whole sets of chromosomes can be seen in syndromes such as triploidy, which means that individuals have three of every chromosome, for a total of 69 chromosomes. An example of this is a hydatidiform molar pregnancy, which is beyond the scope of this series, but will be addressed in future courses.