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History and Phylogeny of Life on Earth (Chapter 25 (Conditions on early…
History and Phylogeny of Life on Earth
Chapter 25
Conditions on early Earth
Abiotic synthesis of small molecules, such as nitrogenous bases and amino acids
Joining of small molecules into macromolecules, such as proteins and nucleic acids
The packaging of these molecules into protocells, droplets with membranes that maintained an internal chemistry different from surroundings
The origin of self-replicating molecules made inheritance possible
Synthesis of Early Compounds
Hydrothermal vents- areas on the ocean floor where heated water and minerals come from the Earth's interior
Alkaline vents- released water with a high ph and warm temperature that may have been more suitable
The abiotic synthesis of RNA monomers came from simpler precursor molecules, meaning they probably occurred spontaneously, without the help of enzymes or ribosomes
Protocells- all organisms must be able to carry both reproduction and energy processing (metabolism), absorption of RNA and the necessary conditions may have occurred in vesicles
Self-replicating RNA- RNA plays a role in protein synthesis, but also function as an enzyme-like catalyst called ribosomes
Fossil Record
Fossil record- based primarily on the sequence in which fossils have accumulated in sedimentary rock layers called strata
Radioactive dating- based on the decay of radioactive isotopes
Half-life- the time required for 50% of the parent isotope to decay
Origin of new groups of organisms- the fossil record shows that the unique features of mammalian jaws and teeth evolved gradually over time, in a series of steps
Origin of Mammals
Synapsid- early synapsids had multiple bones in the lower jaw and single-pointed teeth. The jaw hinge was formed by the articular and quadrate bones
Therapsids- They had large dentary bones, long faces, and specialized teeth, such as large canines and the trend continued in a group called cynodonts.
Early Cynodonts- The dentary was the largest bone in the lower jaw; the temporal fenestra was large and positioned forward of the jaw hinge, and teeth with several cusps. As well they had a synapsid like articular-quadrate hinge.
Later cynodonts- They had teeth with complex cusp patterns, and their lower and upper jaw in two locations. Thy retained the original articular-quadrate hinge and formed a new second hinge between the dentary and squamosal bones.
Very later cynodonts- Cynodonts and early mammals completely lost the original articular-quadrate hinge and left the hinge between the dentary-squamosal hinge as the only hinge between the lower and upper jaws as in living mammals. The articular and quadrate bones migrated into the ear region where they function in transmitting sound. These bones later evolved into hammer and anvil bones of the ear.
Key Events in Life History
Geologic Time
Geologic record; a standard time scale that divides Earth's history into four eons and subdivisions
https://www.digitalatlasofancientlife.org/wp-content/uploads/2018/03/GeologicalTimeScale4.png
Unicellular and Multicellular Organisms
First single-celled organisms- stromatolites are layered rocks that form when certain prokaryotes bind thin film of sediment together
Photosynthesis and oxygen- The free O2 produced probably dissolved in the surrounding water until it reached a high enough concentration to react with elements
The first eukaryotes- endosymbiosis when a prokaryotic cell engulfed a small cell that would evolve into an organelle found in all eukaryotes, the mitochondrion
Early eukaryotes came into existence around 1.8 billion years ago
Cambrian explosion- many present-day animal phyla appeared suddenly in fossils around 535-525 million years ago
Colonization of land- gradual evolution venture out of aquatic environments was associated with adaptations that made it possible to reproduce on land and prevent dehydration
Evolution is not goal oriented
The Rise and Fall of Groups
Continental Drift
Plate tectonics- the continents are part of great plates of Earth's crust that essentially float in the hot mantle
Pangea- supercontinent with all land masses together
Mass Extinction
Mass extinction- large number of species become extinct world-wide
Consequences of mass extinction- by eliminating large number of species, a mass extinction can reduce a thriving and complex ecological community to a pale shadow
Adaptive radiation- periods of evolutionary change in which groups of organisms form new species whose adaptations allow them to fill different roles
Effect of Developmental Genes
Changes in spatial pattern can result from alterations in genes that control the spatial organization of body parts, mastery regulatory genes called homeotic genes determine basic features
Changes in gene sequence new developmental genes arise after new duplication events probably facilitated the origin of novel morphological forms
Changes in gene regulation- a change in nucleotide sequence of a gene may affect its function whenever the gene is expressed, while changes in the regulation of gene expression can be limited to one cell type.
Changes in rate and timing- an evolutionary change in the rate and timing of developmental events can modify species
Chapter 26
Phylogeny
phylogeny- the evolutionary history of a species or group of species
Phylogenies Show Evolutionary Relationships
Binominal- the two-part format of the scientific name
Taxonomy- organisms are named and classified
Hierarchical Classification
Families into Orders
Orders into Classes
Classes into Phyla
Phyla into Kingdoms
Taxon- the named taxonomic unit at any level of the hierarchy
Phylogenetic Tree
Phylogenetic tree- evolution of a group of organisms can be represented by branching
Branching point- represents the common ancestor of two lineages diverging
Sister taxa- groups of organisms that share an immediate common ancestor that is not shared by any other group
Rooted- means that a branch point within a tree represents the most recent ancestor of all the taxa in the tree
Basal taxon- a lineage that diverges from all other members of its group early in the history of the group
Morphology
Homologies- phenotypic and genotypic similarities due to shared ancestry
Analogy- phylogeny that is similarity between organisms due to convergent evolution rather than shared ancestry
Cladistics
Cladistics- is a method of classification of animals and plants according to the proportion of measurable characteristics that they have in common. On a phylogenetic tree the lineages on that branch form a clade
Clades
Clades- a group of organisms believed to have evolved from a common ancestor, according to the principles of cladistics
Monophyletic groups- consist of an ancestral species and all of its descendants.
Paraphyletic groups- consist of an ancestral species and some descendants not all of them
Polyphyletic groups- include distant related species but does not include their most recent common ancestor
All features of organisms arose at some point in the history of life, it should be possible to determine the clade in which each shared derived character first appeared and to use that information to infer evolutionary relationships
Outgroup- is a species or group of species from an evolutionary lineage that is closely related to but not part of the group of species that we are studying (ingroup)
Shared ancestral character- a character that originated in an ancestor of the taxon
Shared derived character- an evolutionary novelty unique to a clade
Gene Duplication and Gene Families
Orthologous genes- the homology is the result of a speciation event and hence occurs between genes found in different species
Paralogous genes- the homology results from gene duplication; hence, multiple copies of these genes have diverged from one another within a species
Molecular clock- an approach for measuring the absolute time of evolutionary change based on the observation that some genes and other regions of genomes appear to evolve at constant rates
Horizontal gene transfer- a process in which genes are transferred from one genome to another through mechanisms such as exchange of transportable elements and plasmids, viral infection, and fusions of organisms