A DNA ladder is a solution of DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 molecules of different lengths used in agarose gel electrophoresis. It is applied to an agarose gel as a reference to estimate the size of unknown DNA molecules. In addition it can be used to approximate the mass of a band by comparison to a special mass

Mass

Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

 ladder.

Structure

Different DNA ladders are commercially available depending on expected DNA length. The 1kb ladder with fragment ranging from about 0.5 kbp

KBP

KBP can mean:* KBP Knowledge Based Processor, is used for processing packets in computer networks* Kilo-base pair , a unit of measurement of DNA or RNA length used in genetics, equal to 1,000 nucleotides....

 to 10 or 12 kbp and the 100 bp ladder with fragments ranging from 100 bp

Base pair

In molecular biology and genetics, the linking between two nitrogenous bases on opposite complementary DNA or certain types of RNA strands that are connected via hydrogen bonds is called a base pair...

 to just above 1000 bp are the most frequent. DNA ladders are often produced by a suitable restriction digest

Restriction digest

A restriction digest is a procedure used in molecular biology to prepare DNA for analysis or other processing. It is sometimes termed DNA fragmentation...

 of a plasmid

Plasmid

In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA. They are double-stranded and, in many cases, circular...

. There are special DNA ladders for supercoiled DNA and RNA.

For example, a λ DNA-HindIII Digest: a common lambda DNA ladder that has band sizes (in base pair

Base pair

In molecular biology and genetics, the linking between two nitrogenous bases on opposite complementary DNA or certain types of RNA strands that are connected via hydrogen bonds is called a base pair...

s) of 23,130; 9,416; 6,557; 4,361; 2,322; 2,027; 564; and 125 bp