Introduction:
Phylogenetic tree also known as evolutionary tree depicts the connection between various species of animals and plants based on their physical and genetic traits. Top points of the trees symbolize descendent common species whereas nodes symbolize common ancestor of descendents. Phylogenetic trees very effectively show the evolution that took place by adaptive and sudden ancestry splits. The Phylogenetic trees can be classified mainly in four types rooted tree, un-rooted tree, bifurcating tree and special tree types.
The basal universal phylogenetic tree inferred from comparative analyses of rRNA sequences.
1. Horizontally acquired variations – Horizontal acquire variations occurs due to horizontal gene transfer. Horizontal gene transfer also known as lateral gene transfer is a procedure where a species integrate genetic material of any other species even when other species is not parent of that species. Horizontal gene transfer is a process which defines cellular evolution due to its nature of bringing variation in species. Horizontal gene transfer was known for a long time but earlier scientists were aware about the limited impact on evolution. For the last two decades we have realized the power of Horizontal gene transfer. It can change the whole genome. For example we can see various protein trees and RNA tree are different in topology because of Horizontal gene transfer. Earlier we use to think that the trees are having flaws or plotted wrongly but those interpretations were not right.
Horizontal gene transfer can be done by various methods. Transformation is a method in which cell get altered due to introduction of genetic material from strange species. In transduction method genetic material moved from one species to another by virus. Another method is bacterial conjugation in which genetic material get transferred by cell contact. Horizontal gene transfer also conducted by gene transfer agents.
Vertically generated variations – Vertically generated variation occurs due to vertical gene transfer. Vertical gene transfer is a procedure where a species integrate genetic material from its parent or any ancestors. Earlier when knowledge about horizontal acquired variations and horizontal gene transfer was not completely developed, genetics was majorly derived from vertical gene transfer.
Vertically generated variations are very limited in character. The variations between parents and its offspring’s are very limited in nature. Horizontal derived variations are major sources of evolution. Vertically generated variations on lineages are the main way for biological difficulties and cellular integration.
2. Cambrian explosion can be recalled as a most puzzling occasion in the history of human life. Before 550 to 600 million year’s changes on the earth were very rapid. Majority of the phylum encountered various diversifications by other species including plants, animals and calcimicrobes. During that time all the species were very simple and formed by one cell. Year after years the rate of change was growing and after approx 80 years the ancestors of all species existing today were emerged. As per scientist the possible reasons for explosion could be increased level of oxygen, snowfall on the earth and increased level of calcium in Cambrian seawater.
Scientist faced lot of difficulties in describing Cambrian explosion as the event happened long time ago but there are few evidence and techniques are existing that provide proof of Cambrian explosion. Some evidences are: body fossils- a very informative way of evidence. Presently we do not have complete records of fossils because of the time and metamorphism. The fossils available from Cambrian fauna are lagerstatten and have supple tissues and it is not difficult to study complete anatomy of those species. Trace fossils – these types of fossils mainly have holes, warren, tracks, feces and feeding marks. These fossils help in studying behavior of that era. Geochemical technique – various chemical marks indicate the rapid changes around Cambrian. These marks are consistent with extinction or with enormous warming due to methane ice. Phylogenetic techniques – this technique helps in working out family tree for specific species. These techniques work by establishing a relationship between species and its ancestors after evaluating the structure of DNA and RNA. Cladistics is one of the techniques which establish link between species by linking similar characteristics.
Special tree type branch of phylogenetic tree is involved in Cambrian explosion. Cladogram type of phylogenetic tree is used in developing tree for species during Cambrian explosion time.
3. Genotype information provide better detailed than phenotype information. Genotype information is more useful while developing phylogenetic tree. Some information that required for phylogenetic tree can only be obtained by genotype like; distinct difference in molecular progression, information contained in genes encoding, phenotype or external features of species change very slowly compare to genetic features.
Genotype information provides full information on species hereditary even if information is not articulated. Phenotype is a type of information that developed by observing the properties of species like behavior, various development and morphology. Phenotype information provides external information about species. Genotype information is internally coded information that used in forming and maintaining a live species. Genotype information is used during the whole life of a species or cell and transferred from one generation to other generation. Genotype information describes the complete process of protein formation, regulation and synthesis. Phenotype information is based on observation and sometimes can be misleading. It is not necessary that genotype always provide complete information. For example DNA molecule consist four nucleotides and while comparing two different species DNA the sequence may be same because of random mutation.
4. The debate on the existence on tree of life is still going on. Scientists around the world are skeptical about its existence. The trees of life have different definitions in different subjects. People are having tree of life in biology, religion, mythology and various areas. In the field of science there are various theories about tree of life which conflict with each other. The theory of life is based on cell evolutions. All the theories developed by scientist are based on their own understanding, assumptions, available evidence and other supporting facts.
The existence of life on earth happened long time ago and till now scientist are not having a complete information about the various species and their phylogenetic trees. During the evolutions lot of variations horizontal and vertical took places, lot of information due to random mutation gone missing. There is still a big question mark on the existence of tree of life.
Conclusion:
The universal phylogenetic tree represents the true picture of the genealogy and it opens the doors of the past for the people and allows them to see the past. Further it also portrays a picture of the future and helps the biologist in their several researches and studies.
References
Willi Hennig, D. Davis and Rainer Zangerl. (1999). Phylogenetic systematics. Champaign: University of Illinois Press.
Cambrian Explosion. (n.d.). Retrieved December 25, 2011, from www.fossilmuseum.net: http://www.fossilmuseum.net/Paleobiology/CambrianExplosion.htm
E. O. Wiley and Bruce S. Lieberman. (2011). Phylogenetics: Theory and Practice of Phylogenetic Systematics. New Jersey: John Wiley & Sons.
Modern Phylogenetics. (n.d.). Retrieved December 25, 2011, from www.bio.cmu.edu: https://www.bio.cmu.edu/courses/03441/TermPapers/99TermPapers/GenEvo/phylogeny.htm
Woese, C. R. (2000, May 22). Interpreting the universal phylogenetic tree. Retrieved December 25, 2011, from www.pnas.org: http://www.pnas.org/content/97/15/8392.full.pdf
Woese, C. R. (2002). On the evolution of cells. PNAS , 8742–8747.
