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Chapter 17: The Tree of Life
Terms in this set (31)
- the science of naming and classifying organisms.
- gives scientists a standard way to refer to species and organize the diversity of living things.
- Linnaean taxonomy classifies organisms based on their physical and structural similarities.
- a taxon is a group of organisms in a classification system. plural, taxa.
- the basic taxon in the Linnaean system is the species.
- a two-part scientific naming system using Latin words.
- scientific names always written in italics.
- two parts are the genus name and species.
- includes one or more physically similar species that are thought to be closely related.
- genus names are always capitalized.
- second part of the name.
- can refer to a trait of the species, the scientist who first described it, or its native location.
- always lowercase.
- always follows genus name; never written alone.
why do biologists use scientific names?
- scientific names help scientists to communicate.
- many species have very similar common names.
- one species may have many different common names.
- pills bugs, roly-poly, sow bug, potato bug.
Linnaeus's classification system has seven levels, or taxa.
- from the most general to the most specific, these levels are Kingdom, Phylum, Class, Order, Family, Genus, and Species.
- the term division is often used instead of phylum for plants and fungi.
- each level is included in the level above it.
- levels get increasingly specific from kingdom to species.
- Kings Play Chess On Fuzzy Green Stools.
The Linnaean classification system has limitations.
- Linnaeus taxonomy doesn't account for molecular evidence.
- the technology didn't exist during Linnaeus's time.
- his system focuses on physical similarities alone.
- physical similarities are not always the result of close relationships.
- unrelated species can evolve similar traits through convergent evolution.
- genetic similarities more accurately show evolutionary relationships.
- classification based on common ancestry.
- similar traits between species are often the result of sharing a common ancestor, such as the ancestor shared by dogs and wolves.
- modern classification is based on figuring out evolutionary relationships using evidence from living species, the fossil record, and molecular data.
- the evolutionary history for a group of species.
- phylogenies can be shown as branching tree diagrams.
the most common method used to make evolutionary trees is called cladistics.
- the goal of cladistics is to place species in the order in which they descended from a common ancestor.
- an evolutionary tree that proposes how species may be related to each other through common ancestors.
- a group of species that shares a common ancestor.
- each species in a clade shares some traits with the ancestor.
- through the course of evolution, certain traits change in some species of a clade, but stay the same in other species.
- each species in a clade has some traits that have changed from its ancestors over evolutionary time.
- the traits that can be used to figure out evolutionary relationships among a group of species are those that are shared by some species, but are not present in others.
- more closely related species share more derived characters.
- cladograms are made by figuring out which derived characters are shared by which species.
- a group of species that shares no derived characters with the other groups being studied is called an out group.
new technology allows biologists to compare groups of species at the molecular level
- molecular evidence reveals species' relatedness.
- molecular data may confirm classification based on physical similarities.
- evolutionary tree is always a work in progress.
- molecular data may lead scientists to propose a new classification.
- proteins and genes are used to help learn about evolutionary relationships; DNA is sully given the last word by scientists.
- the more similar to each other the genes of two species are, the more closely related the species are likely to be.
molecular clocks use mutations to estimate evolutionary time
- mutations add up at a constant rate in related species.
- Pauling and Zuckerkandl proposed a new way to measure evolutionary time.
- they compared amino acid sequences of hemoglobin from a wide range of species.
- the more distantly related two species are, the more amino acid differences there are in their hemoglobin.
- models that use mutation rates to measure evolutionary time.
- the more time that has passed since two species have diverged from a common ancestor, the more mutations will have built up in each lineage, and the more different the two species will be at the molecular level.
- the rate of mutations is the ticking of the molecular clock.
linking molecular data with real time
- this link comes from the timing of a geologic event that is known to have separated the species they are studying.
- if scientists know when the species began to diverge from a common ancestor, they can find the mutation rate for the molecule they are studying.
a link can also come from fossil evidence
- Pauling and Zuckerkandl compared their molecular data with the first appearance of each type of organism in the fossil record.
- the number of amino acid differences increases with the evolutionary time between each group of species.
mtDNA and rRNA provide two types of molecular clocks
- different molecules have different mutation rates.
- depending on how closely related two species are, scientists choose a molecule with an appropriate mutation rate to use as a molecular clock.
mitochondrial DNA (mtDNA)
- DNA found only in mitochondria.
- the mutation rate of mtDNA is about 10 times faster than that of nuclear DNA.
- higher rate, better for studying closely related species.
- passed down unshuffled from mother to offspring.
- mutations in mtDNA have been used to study the migration routes of humans over the past 200,000 years.
ribosomal RNA (rRNA)
- useful for studying distantly related species, such as species that are in different kingdoms or phyla.
- when studying the relationships among species over longer time scales, it is best to use a molecule that has a lower mutation rate.
- many conservative regions.
- over long periods of geologic time, mutations that do build up in the rRNA of different lineages are relatively clear and can be compared.
- Carl Woese first used rRNA to establish that archaea diverged from the common ancestor they share with bacteria almost 4 billion years ago.
classification is always a work in progress
- tree of life shows our most current understanding.
- new discoveries can lead to changes in classification.
changes in the tree of life
- until 1866: only two kingdoms, Animalia and Plantae.
- 1866: all single celled organisms moved to kingdom Protista.
- 1938: prokaryotes, no nucleus so bacteria, moved to kingdom Monera.
- 1959: fungi moved to own kingdom in Eukarya domain.
- 1977: kingdom Monera split into kingdoms and domains Bacteria and Archaea.
why was Monera split?
- bacteria and monera had very different cell wall chemistry.
the three domains in the tree of life are Bacteria, Archaea, and Eukarya
- domains are above the kingdom level.
- proposed by Carl Woese based on rRNA studies of prokaryotes.
- domain model more clearly shows prokaryotic diversity.
- includes prokaryotes in the kingdom Bacteria.
- one of the largest groups on Earth.
- can be classified for their shape, their need for oxygen, and whether they cause disease.
- includes prokaryotes in the kingdom Archaea.
- known for their ability to live in extreme environments, such as deep sea vents and hot geysers.
- includes all eukaryotes.
- eukaryotic cells have a distinct nucleus and membrane bound organelles.
- may be single celled, such as most protist. they may be colonial, such as algae or multicellular like humans.
- includes the kingdoms Protista, Plantae, Fungi, and Animalia.
- Fungi cannot move and decompose.
- eukaryotic or prokaryotic: no nucleus or nucleus.
- autotroph or heterotroph: make their own food or rely on other organisms for their food.
- does it reproduce sexually or asexually.
classifying Bacteria and Archaea
- many of these organisms transfer genes among themselves outside of typical reproduction.
- this sharing of genes blurs the lines between species as we define them in Linnaean systems.
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