What are the different types of DNA?

There are two types of DNA based on location – Nuclear DNA and Mitochondrial DNA. 

Nuclear DNA: Nuclear DNA (nDNA), also known as autosomal DNA, is located in the nucleus of eukaryotic cells. Every cell contains two copies of nDNA. Nuclear DNA is diploid – it inherits chromosomes from both parents. It is composed of 46 chromosomes. 23 chromosomes are inherited from the father and 23 from the mother.  nDNA chromosomes have a linear structure that are open at both ends. 

Mitochondrial DNA: Mitochondrial DNA (mtDNA) is located in the mitochondria. Every cell contains around 100-1000 copies of mitochondrial DNA. mtDNA is haploid. It is inherited from one source – the mother. Mitochondrial chromosomes have closed, circular structures. 

DNA can also be classified into 6 types based on structural diversity. 

B-DNA: This is the most common DNA conformation under normal physiological conditions. It has a right-handed double helix structure. 

 A-DNA: A-DNA is also a right-handed double helix but is rarely found under normal physiological conditions. It typically appears only when environmental humidity is lower than 75% to protect the DNA from extreme dehydration. 

Z-DNA: Z-DNA has a left handed double helical structure with a pronounced zigzag pattern in the phosphodiester backbone. It is narrower than other types of DNA and is inherently unstable and transient in nature, appearing only when subjected to certain biological activities and disappearing immediately.   

C-DNA: This is an unstable form that DNA assumes at relatively low humidity less than 66% and in the presence of specific ions such as Li+ and Mg2+. It contains a similar nucleotide conformation as B-DNA but at a different ratio. C-DNA does not occur naturally in living organisms. 

D-DNA: D-DNA is a rare variant as it lacks the Guanine (G) base unit. It has eight base pairs per helical turn. 

E-DNA: Also known as extended or eccentric organismal DNA,  E-DNA originates from cellular material such as mucous, hair, skin, gametes, carcasses, and secreted fecal matter, which are shed by organisms into the environment. E-DNA does not last more than 7 to 21 days, depending on environmental conditions such as heat, exposure to acidity, or radiation.