A dendrogram is a tree

Tree (graph theory)

In mathematics, more specifically graph theory, a tree is an undirected graph in which any two vertices are connected by exactly one simple path. In other words, any connected graph without cycles is a tree...

 diagram frequently used to illustrate the arrangement of the clusters produced by hierarchical clustering

Hierarchical clustering

In statistics, hierarchical clustering is a method of cluster analysis which seeks to build a hierarchy of clusters. Strategies for hierarchical clustering generally fall into two types:...

. Dendrograms are often used in computational biology

Computational biology

Computational biology involves the development and application of data-analytical and theoretical methods, mathematical modeling and computational simulation techniques to the study of biological, behavioral, and social systems...

 to illustrate the clustering of gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

s or samples.

For a clustering example, suppose this data is to be clustered using Euclidean distance

Euclidean distance

In mathematics, the Euclidean distance or Euclidean metric is the "ordinary" distance between two points that one would measure with a ruler, and is given by the Pythagorean formula. By using this formula as distance, Euclidean space becomes a metric space...

 as the distance metric

Metric (mathematics)

In mathematics, a metric or distance function is a function which defines a distance between elements of a set. A set with a metric is called a metric space. A metric induces a topology on a set but not all topologies can be generated by a metric...

.
The hierarchical clustering

Hierarchical clustering

In statistics, hierarchical clustering is a method of cluster analysis which seeks to build a hierarchy of clusters. Strategies for hierarchical clustering generally fall into two types:...

 dendrogram would be as such:

Here the top row of nodes represent data, and the remaining nodes represent the clusters to which the data belong, and the arrows represent the distance.

See also

• Cladogram
  Cladogram
  A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
  
  
• Hierarchical clustering
  Hierarchical clustering
  In statistics, hierarchical clustering is a method of cluster analysis which seeks to build a hierarchy of clusters. Strategies for hierarchical clustering generally fall into two types:...
  
  
• MEGA
  MEGA, Molecular Evolutionary Genetics Analysis
  MEGA, Molecular Evolutionary Genetics Analysis, is a freely available software to aid scientists and students in making dendrograms, or phylogenetic trees using nucleotide or protein sequences...
  
  , a free software for drawing dendrograms.
• yEd
  YEd
  yEd is a freely available, general-purpose diagramming software with amulti-document interface.It is a cross-platform application written in Java that runs on Windows, Linux, Mac OS, or any platform that supports the JVM....
  
  , a free software for drawing and automatically arranging dendrograms.