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Chapter 27

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Chapter 27: Phylogenic Trees Recall: Hybrid zone: an evolutionary neutral area where hybrids co-exist. Be able to estimate phylogenies. -Phylogenic trees document the evolutionary relationships among organisms and are estimated form data. -Adaptive radiations are a major pattern in the history of life. They are instances od rapid diversification associated with new ecological opportunities and new morphological innovations. - We have to infer or estimate phylogenies. Computers measure “distance between species”. The statistical analysis estimates the separation of taxon’s.Adistance matrix compares how different the sequence the individuals are. - A branch represents a population through time. - Apoint where two branches diverge is called a node. This is where a species diverges. - a tip or terminal node is the end point of a branch, which represents groups (a species or larger taxon) that is living today or ended in extinction. How do researchers estimate phylogenies? -Phylogenetic trees are effective way of summarizing data on the evolutionary history of a group of organisms. -The genealogical relationships of a species cannot be definitively known. -To infer historical relationships between organisms, researchers analyze morphological or genetic characteristics of species. Researchers do this be looking at fossil records and DNAsequencing. -Researcher use two approaches when constructing the actual phylogenic tree: 1. Phenetic approach: estimating trees using statistical summaries of overall similarities of organisms. Look t differences or similarities. 2. Cladistic approach: inferring trees based on synapomorphies (two or more organisms have a trait), recognizing shared characteristics that re derived from previous species, allowing researchers to analyze monopyholetic groups. (the simplest is best), The phylogeny is constructed with the least amount of changes possible. You choose the phylogeny that occurs the least amount of changes. Synaptomorphy is an evolutionary innovation ex nipples. It is a newly derived feature of something. How can Biologists distinguish Homology from Homoplasy? ­ The issue that traits can be similar in two species not because those traits were present in a common ancestor but because similar traits evolved independently in two distinct groups. Homology translates to “same source”. Similar traits are inherited from a common ancestor. Similarity due to shared ancestry. Ex: the Hox genes are present in fruit flies and humans due to common ancestry and are involved in the development of the embroyo. They are strings in specific order horizontally and transcribed from head of the embryo to the end o the body. This set of genes were then inherited by descendant populations. Homology is more frequent than Homoplasy. Homoplasy “same form” occurs when two traits are similar for reasons other than common ancestry. The flying structure of wings ex insects and birds. The homoplasy is that they are not related but both have wings. The have the similar bones. (Similarities not derived from ancestry). Key to look for is their ancestors share the traits. Even though species look alike they may not be closely related at all. ­ Convergent evolution occurs when natural selection favours similar solutions to the environment (homoplasy). Convergent traits are also called analogous traits. These trait do not occur in a common ancestor of the similar species. When for example dolphins and fish both evolved gills but do not share ancestral history. ­ The researchers use a “parsimony” to better understand the true meaning of the data. Under a parsimony, the most likely explanation that implicates the least amount of change is thought of as true. ­ Phylogenies can also be based on transposable elements due to the fact that they are unique to each organism but related in species. ­ Even though bone structure is the same, bats and birds evolved independently of one another. Fossils: direct evidence of past living organisms, physically preserved. It tells us about mass extinctions and phylogenies. Limitations of fossilization records Habitat Bias: Organisms that live in certain areas where sediments are actively being deposited including beaches, swamps ect. That are much more likely to form fossils. Some fossils will preserve better in different area proposing a bias in what species are preserved. Taxomic and tissue bias: Slow decay is almost always essential to fossilization, so organisms with hard part such as bones or shells are most likely to leave fossil evidence. Temporal Bias: Recent fossils are much more common than ancient fossils. This causes a temporal bias in the record, only having recently made fossils. Strata more close to the surface are more often found. Abundance bias: Organisms that are most abundant, and widespread leave much more evidence more often than other species that are not as widespread. Life’s time line Precambrian Period: (4.6 biollion-542 million) Includes: Hadean,Achaean, Proterozoic. ­ Life was exclusively unicellular for most of Earth’s history and oxygen was absent form the oceans and atmosphere. Phanerzioc eon: The interval between 542 mya and the present is called the Phanerzoic eon. This eon has divided into three eras. Each of these eras is subdivided into periods. (pg 528) 1. Paleozoic: (ancient life era) The Paleozoi
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