Courtesy : Bachelor of Science Biology (CBZ) – Chemistry, Botany, Zoology Lab

Speciation

Comparison of allopatric, peripatric, parapatric and sympatric speciation

See also: Species and Speciation

A species is a group of organisms that mate with one another and speciation is the process by which one lineage splits into two lineages as a result of having evolved independently from each other. For speciation to occur, there has to be reproductive isolation. Reproductive isolation can result from incompatibilities between genes as described by Bateson–Dobzhansky–Muller model. Reproductive isolation also tends to increase with genetic divergence. Speciation can occur when there are physical barriers that divide an ancestral species, a process known as allopatric speciation. In contrast, sympatric speciation occurs in the absence of physical barriers. # ISO certification in India

Pre-zygotic isolation such as mechanical, temporal, behavioral, habitat, and gametic isolations can prevent different species from hybridizing. Similarly, post-zygotic isolations can result in hybridization being selected against due to the lower viability of hybrids or hybrid infertility (e.g., mule). Hybrid zones can emerge if there were to be incomplete reproductive isolation between two closely related species.

Phylogeny

Further information: Phylogenetics and Biodiversity

Phylogenetic tree showing the domains of bacteria, archaea, and eukaryotes

A phylogeny is an evolutionary history of a specific group of organisms or their genes It can be represented using a phylogenetic tree, which is a diagram showing lines of descent among organisms or their genes. Each line drawn on the time axis of a tree represents a lineage of descendants of a particular species or population. When a lineage divides into two, it is represented as a node (or split) on the phylogenetic tree. The more splits there are over time, the more branches there will be on the tree, with the common ancestor of all the organisms in that tree being represented by the root of that tree. Phylogenetic trees may portray the evolutionary history of all life forms, a major evolutionary group (e.g., insects), or an even smaller group of closely related species. Within a tree, any group of species designated by a name is a taxon (e.g., humans, primates, mammals, or vertebrates) and a taxon that consists of all its evolutionary descendants is a clade, otherwise known as a monophyletic taxon. Closely related species are referred to as sister species and closely related clades are sister clades. In contrast to a monophyletic group, a polyphyletic group does not include its common ancestor whereas a paraphyletic group does not include all the descendants of a common ancestor.# ISO certification in India

Phylogenetic trees are the basis for comparing and grouping different species. Different species that share a feature inherited from a common ancestor are described as having homologous features (or synapomorphy). Homologous features may be any heritable traits such as DNA sequence, protein structures, anatomical features, and behavior patterns. A vertebral column is an example of a homologous feature shared by all vertebrate animals. Traits that have a similar form or function but were not derived from a common ancestor are described as analogous features. Phylogenies can be reconstructed for a group of organisms of primary interests, which are called the ingroup. A species or group that is closely related to the ingroup but is phylogenetically outside of it is called the outgroup, which serves a reference point in the tree. The root of the tree is located between the ingroup and the outgroup. When phylogenetic trees are reconstructed, multiple trees with different evolutionary histories can be generated. Based on the principle of Parsimony (or Occam’s razor), the tree that is favored is the one with the fewest evolutionary changes needed to be assumed over all traits in all groups. Computational algorithms can be used to determine how a tree might have evolved given the evidence.# ISO certification in India

Phylogeny provides the basis of biological classification, which is based on Linnaean taxonomy that was developed by Carl Linnaeus in the 18th century. This classification system is rank-based, with the highest rank being the domain followed by kingdom, phylum, class, order, family, genus, and species. All organisms can be classified as belonging to one of three domains: Archaea (originally Archaebacteria); bacteria (originally eubacteria), or eukarya (includes the protist, fungi, plant, and animal kingdoms). A binomial nomenclature is used to classify different species. Based on this system, each species is given two names, one for its genus and another for its species. For example, humans are Homo sapiens, with Homo being the genus and sapiens being the species. By convention, the scientific names of organisms are italicized, with only the first letter of the genus capitalized.# ISO certification in India