How is the tree length in bootstrap phylogeny trees calculated?

• Buffer
• Tweet

Bootstrapping is used in biology in the field of systematics. Phylogenic or evolutionary trees are used in the process. The purpose is to determine confidence values for the groupings of organisms that belong to a particular family or a species and which are represented as hypothetical constructs on those evolutionary trees.

Phylogenic or evolutionary trees can be estimated from either DNA or RNA sequence data. Organisms with common ancestors are arranged on branches of the tree with the organisms at the node and the common ancestor at the branch. Since the data on these trees are hypothesized evolutionary similarities and differences, there needs to be a way of estimating the length of the tree. In 1985, the idea of using bootstrapping analysis was introduced to scientists by J. Felsenstein. The bootstrap is a technique based on computer analysis to determine the accuracy of any statistical estimate. Bootstrapping analysis presents scientists with a way to determine the strength of the support for nodes on phylogenic or evolutionary trees. This is done by assigning a specific number for each node and this reflects the percent value of the bootstrap tree that resolves that particular clade. A clade is a single branch on a phylogenic tree that represents all the organisms that have a common ancestor.

The bootstrap has been found to be useful by scientists in situations where analytical methods are not considered to be practical. For example, they are used in complicated estimation problems that are not parametric. Some researchers, however, have argued that Felsenstein’s bootstrap method was biased downwards. The confidence values are consistently too conservative to assess the accuracy of particular phylogenic trees. But other researchers do not agree with this assessment. They maintain that the bootstrap is accurate for a first order of statistical analysis of phylogenic trees. They believe that Felsenstein’s method provides a good first approximation of the level of confidence in observed clades. Furthermore, they maintain that the bootstrap methods can be refined to provide even more accurate confidence assessments of phylogenic trees.

Bootstrapping specifically involves making N random samples of sites from the alignments of groups. In this process, N should be large, as much as 500 to 1000 samples. N trees are drawn, using, for example, one from each sample. They are then counted to determine how many times each grouping from the original tree is found to occur in the sample trees. A seed number must be supplied for each random number generator. The same result will occur for different runs using the same seed number.

Bootstrap methods are used to determine what biologists call the stability and the reliability of the estimate of a phylogenic tree value. Statisticians call this stability and reliability measure “robustness”. If a bootstrap value for a certain clade is high, close to 100%, for example, this indicates that there is uniform support for the view that this clade is a genuine evolutionary group.

Bootstrapping is also used to produce a confidence interval for a forecast by using the entire estimation of the actual sampling distribution. Bootstrapping of phylogenic trees is used in the field of biological study called systematics. Systematics uses binary rooted phylogenic trees that connect families or species to their common ancestors. The trees as well as the ancestors are hypothetical inferences because there is no actual fossil data available. The data is compiled using DNA or RNA protein sequences. These are represented on the phylogeniclabeled by species and columns signify positions in the sequence of the genome.

In recent practice, phylogenic trees have even been used for environmental surveillance and in court cases. For example, whale watch teams track the whales’ phylogenic tree data. Immunologists and microbiologists use phylogenic trees to determine the origins and development of bacteria and viruses such as HIV, influenza and other strains of bacteria that evolve quickly.

Resource by Will

I am the editor for TheFreeResource.com, and owner of LinchpinSEO, a small business content creation company. The Free Resource has a select community of talented writers, teachers, and business people (and we are always looking for more) that bring you the most trusted resources on the web and credible articles about many topics.

Related Research For Teachers, Students, and Kids