Chapter 26 - Phylogeny and the Tree of Life

Phylogenies demonstrate evolutionary connections.

Because of shared ancestry, organisms share many features (as shown in the image attached). As a result, knowing a species' evolutionary history may teach us a lot about it. For example, an organism's close relatives are likely to share many of its genes, metabolic pathways, and structural proteins.

Later in this part, we'll look at practical uses of such knowledge, but first, we'll look at how creatures are called and categorized, which is the scientific field of taxonomy. We'll also look at how to understand and use graphs depicting evolutionary history.

In casual usage, common names for creatures such as monkey, sparrow, and lilac communicate meaning, but they may also generate misunderstanding. For example, each of these names relates to more than one species. Furthermore, several popular names may not correctly represent the type of creature they represent.

Consider the following three "fishes": jellyfish (a cnidarian), crayfish (a tiny, lobster-like crustacean), and silverfish (an insect). And, of course, various languages have different names for the same creature.

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Biologists use Latin scientific names to prevent misunderstanding when speaking about their findings. The two-part structure of the scientific name, known colloquially as a binomial, was introduced in the 1st century, as shown in the image attached.

Linnaeus not only named species but also classified them into a hierarchy of progressively comprehensive groups.

• The first classification is incorporated into the binomial: species that appear to be closely related are classified as belonging to the same genus.

The leopard (Panthera pardus), for example, is part of a genus that also contains the African lion (Panthera leo), the tiger (Panthera tigris), and the jaguar (Panthera onca).

Taxonomists use ever more extensive categorization categories beyond genera. The Linnaean system, named after Linnaeus, groups related genera into families, families into orders, orders into classes, classes into phyla (singular, phylum),

The relationship between categorization and phylogeny The branching patterns of phylogenetic trees can be reflected in hierarchical categorization. This tree depicts the evolutionary connections of some of the species in the order Carnivora, which is a branch of the class Mammalia. categorization should be fully based on evolutionary links

Names are only allocated to groupings that share a common ancestor and all of its descendants under such systems. As a result of this method, certain popularly known groups would merge with other groups that were previously at the same level of the Linnaean system. For example, because birds originated from a group of reptiles known as Aves (the Linnaean class that birds belong to),

Morphological and genetic data are used to infer phylogenies. Creatures with comparable morphologies or DNA sequences are more likely to be linked than organisms with radically diverse shapes and genetic sequences.

To determine phylogeny, homology (similarity owing to common ancestors) must be differentiated from analogy (similarity due to convergent evolution).

Computer algorithms are used to align similar DNA sequences and detect molecular homologies from accidental matches across taxa that split many years ago. Phylogenetic trees are built using shared characteristics.

A clade is a monophyletic group consisting of an ancestor species and all of its descendants. Clades can be recognized by the derived characteristics they share. The most parsimonious tree among phylogenies is the one that requires the fewest evolutionary changes.

The most probable tree is the one with the most likely changing pattern. A vast variety of data supports well-supported phylogenetic theories. The genome contains information about an organism's evolutionary history.

• The term Orthologous genes are homologous genes that have been discovered in different species as a result of speciation. Paralogous genes are homologous genes within a species caused by gene duplication; such genes might diverge and potentially take on new roles. Many orthologous genes can be found in distantly related animals.

Molecular clocks aid in the tracking of evolutionary time. Some sections of DNA change at a constant enough pace to act as a molecular clock, a way of determining the age of past evolutionary events based on genetic change.

Other DNA regions alter in an unpredictable manner.

According to molecular clock analysis, the most prevalent strain of HIV crossed from primates to humans in the early 1900s. Our knowledge of the tree of life evolves in response to new information.

Previous categorization methods gave birth to the present concept of the tree of life, which is divided into three major domains:

• Bacteria

• Archaea

• Eukarya.

Phylogenies based on rRNA genes show that eukaryotes are most closely related to archaea, whereas data from other genes show a closer connection to bacteria.

According to genetic studies, significant horizontal gene transfer has occurred throughout life's evolutionary history.