[Biology Class Notes] on Phylogeny Pdf for Exam

What is Phylogeny?

Phylogeny can be defined as an evolutionary history of a species or group as there are about 100 million species living on earth today. The morphological and biochemical evidence suggests that all the organisms are genetically related. A situation where the genealogical relationships of the organisms can be represented in the form of an evolutionary tree, that is termed as a Phylogenetic tree. In this, the species or groups are organized in such a way that it helps to know how they evolved from the common ancestors. Phylogeny helps in the details of how the genes, genomes and species evolve. It is useful for fundamental and numerical applications. 

 

Phylogenetic Trees

The phylogenetic tree is also known as the cladogram. The species or the groups are found at the tips of the lines known as the tree branches. The evolution of species evolved from a common ancestor is exhibited by how the branches connect. The branch points represent the most recent common ancestor of all the groups descended from that common point. Some cladograms are blocky, while the others are diagonal. However, the orientation of the tree does not change the information. In a phylogenetic tree, if two species have the more common recent ancestor, they are more related than those with a less recent common ancestor.

 

Applications of Phylogenetics

Phylogenetics has the following applications:-

 

With the help of phylogeny, the Linnaean classification of species is known. Based on the sequence data, more accurate descriptions of patterns of relatedness are available.

 

The DNA in case of a crime scene or paternity disputes is assessed by phylogeny.

 

Phylogenetic approaches can be used to know about a new pathogen outbreak. It helps to know the species the pathogen is related to and the source of its transmission.

 

Phylogeny helps the conservation biologists to make the correct decisions about which species they should try to prevent extinction.

 

The algorithms developed for phylogenetics are also used in software development in other fields. 

 

Ontogeny and Phylogeny

Ontogeny is the course of development of an individual organism. It begins at the time of fertilization and includes all the developmental events at the time of birth and thereafter.

The ancestral characters are often preserved in the development of an organism. For eg., the chick and human embryos generally undergo a stage during their development wherein they have slits and arches in their neck similar to the gill slits and arches of a fish. This suggests that humans and chicks share a common ancestor with fish. These developmental characters can be used to create phylogenetic trees.

It is believed that during development, an organism progresses through each of the adult stages of evolutionary history. This states that “ontogeny recapitulates phylogeny”. For instance, a chick goes through the following stages of evolutionary history during the development- a single cell, a multicellular invertebrate, fish, reptile, bird, and then forms the chick. However, the statement is controversial and cannot be proved in all the organisms.

For some years, the organisms have evolved into more derivative forms. The new generations retain most of their ancestral features. It becomes easy for them to get adjusted in the environment they live in as these features get modified with additional novel traits. Phylogeny helps us to know the similarities and differences between plants, animals, and microorganisms.

 

Difference Between Ontogeny and Phylogeny

The development of an organism is defined as Ontogeny while phylogeny refers to how the organisms have evolved.

Let us take an example of a chicken, the ontogeny will explain the entire development cycle of the chicken right from the single cell. Now let’s take an example of an ostrich and assume that it descended from the family of chickens, phylogeny will explain how the chicken evolved into an ostrich, i.e., it will explain the evolutionary process.