{"id":309,"date":"2024-03-23T10:03:17","date_gmt":"2024-03-23T10:03:17","guid":{"rendered":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/?post_type=chapter&p=309"},"modified":"2024-11-18T13:14:36","modified_gmt":"2024-11-18T13:14:36","slug":"6-3-phylogenetics","status":"publish","type":"chapter","link":"https:\/\/pressbooks.justwrite.in\/interactive-biology-secondary\/chapter\/6-3-phylogenetics\/","title":{"raw":"7.3 Phylogenetics","rendered":"7.3 Phylogenetics"},"content":{"raw":"
\r\n
\r\n
\r\n
\r\n
<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n
\r\n
\r\n
\r\n
\r\n
\r\n\r\nThe study of evolutionary relationships among organisms is called Phylogenetics.\u00a0It reconstructs the evolutionary history of species and charts their relationships in a phylogenetic tree using genetic, morphological, and biochemical data. Understanding the relationships between species, the history of their evolutionary divergence, and the evolution of features across time is made easier by phylogenetics.\r\n

Phylogenetic Trees<\/strong><\/h2>\r\nTo illustrate the evolutionary relationships and paths between organisms, scientists employ a particular kind of model known as a phylogenetic tree<\/strong>\u00a0 also called as evolutionary trees.<\/strong> It is an illustration of the evolutionary links between individuals or groups of organisms\u00a0 . As the suggested linkages cannot be verified in the past, scientists view phylogenetic trees as a hypothesis of the evolutionary past.\r\n

Terminology that characterizes a phylogenetic tree.<\/h2>\r\n
The lines in the tree are called branches. Branches<\/strong> on the tree indicate lineages of organisms. <\/span><\/strong>At the tips of the branches are present-day species or sequences known as taxa (the singular form is taxon) or operational taxonomic units.<\/span>The connecting point where two adjacent branches join ( branch point) is called a node<\/strong>, which represents a common ancestor.In a phylogenetic tree, closely related organisms are joined by nodes. These nodes suggest common ancestry.\u00a0 two taxa stemming from the same most recent node are called\u00a0 sister taxa.<\/strong><\/span><\/span><\/div>\r\n
<\/div>\r\n
Rooted and Unrooted trees\u00a0<\/strong><\/div>\r\nA common ancestor is represented by a single lineage at the base of many phylogenetic trees. Such trees are referred\u00a0 as rooted phylogenetic tree<\/strong>, indicating that all of the creatures shown in the diagram are related to a single ancestral lineage, usually drawn from the bottom or left. The three domains of bacteria, archaea, and eukarya branch off from a single point in the rooted phylogenetic tree.In this image, the little branch that plants and animals\u2014including humans\u2014occupy demonstrates how recent and insignificant these groupings are in relation to other species. Unrooted\u00a0 phylogenetic trees<\/strong> reveal links between species but not a common ancestor.\r\n\r\n\"\"\r\n\r\nClade or monophyletic group\u00a0<\/strong>\r\n
A group of taxa descended from a single common ancestor is defined as a clade or monophyletic group. <\/strong>In a monophyletic group, two taxa share a unique common ancestor not shared by any other taxa. They are also referred to as sister taxa to each other (e.g., taxa B and C). Example: In mammals, the clade of primates includes humans, chimpanzees, gorillas, and all other primates with their common ancestor.<\/span>\r\nThe branch path depicting an ancestor\u2013descendant relationship on a tree is called a lineage.\u00a0<\/strong><\/div>\r\n
<\/div>\r\n<\/div>\r\n
Paraphyletic group<\/strong><\/div>\r\n
\r\n
When a number of taxa share more than one closest common ancestors, they do not fit the definition of a clade.In this case, they are referred to as paraphyletic (e.g., taxa B, C, and D).<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\"File:Taxonomy<\/div>\r\n
\"Taxonomy and Phylogenetics\"<\/a>\u00a0by\u00a0<\/span>BoldLuis via Creative commons .org via wikimedia commons<\/a>is licensed under\u00a0<\/span>CC BY-SA 4.0<\/a><\/div>\r\n

Tree topology<\/strong><\/h2>\r\n
\r\n
The branching pattern in a tree is called tree topology. <\/strong>When all branches bifurcate on a phylogenetic tree, it is referred to as dichotomy. <\/strong>In this case, each ancestor divides and gives rise to two descendants.<\/div>\r\n
Sometimes, a branch point on a phylogenetic tree may have more than two descendents, resulting in a multifurcating node. The phylogeny with multifurcating branches is called polytomy. <\/strong>A polytomy can be a result of either an ancestral taxon giving rise to more than two immediate descendants simultaneously during evolution, a process known as radiation, or\u00a0 \u00a0an unresolved phylogeny in which the exact order of bifurcations cannot be determined precisely<\/span><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
<\/div>\r\n
<\/div>\r\n
\"\"<\/div>\r\n
\r\n
\r\n
\r\n
\r\n
\r\n
\r\n\r\nForms of Tree Representation\u00a0<\/strong>\r\n\r\nPhylogram and Cladogram<\/strong>\r\n
The topology of branches in a tree defines the relationships between the taxa. The trees can be drawn in different ways, such as a cladogram or a phylogram.<\/div>\r\n
In a phylogram<\/strong>, the branch lengths represent the amount of evolutionary divergence. Such trees are said to be scaled.The scaled trees have the advantage of showing both the evolutionary relationships and information about the relative divergence time of the branches.<\/div>\r\n
In a cladogram<\/strong>, however, the external taxa line up neatly in a row or column. Their branch lengths are not proportional to the number of evolutionary changes and thus have no phylogenetic meaning. In such an unscaled tree, only the topology of the tree matters, which shows the relative ordering of the taxa.<\/div>\r\n
\"\"<\/div>\r\nMolecular Phylogenetics<\/strong>:\r\n\r\nenables researchers to track lineages back to common ancestors by analyzing evolutionary relationships using DNA, RNA, or protein sequences.\r\nMolecular techniques have transformed phylogenetics by offering information that helps elucidate connections in situations when morphological evidence is unclear or lacking.\r\n\r\nMethods of Building Phylogenetic Trees<\/span>\r\n
    \r\n \t
  1. Distance Methods<\/strong>:\r\n