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BIO152H5 (140)
Chapter 1

Chapter 1.odt

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Fiona Rawle

Chapter 1 Biology and the Tree of Life Biological science was founded with the development of : (1) the cell theory (2) the theory of evolution by natural selection. Aphylogenetic tree is a graphical representation of the evolutionary relationships among species. Phylogenies can be established by analyzing similarities and differences in traits. Biologists ask questions, generate hypotheses to answer them, and design experiments that test the predictions made by competing hypotheses. The Tree of life The cell theory and the theory of evolution by natural selection imply that all species come from preexisting species and that all species, past and present, trace their ancestry back to a single common ancestor. Speciation is a divergence process in which natural selection has caused populations of one species to diverge to form new species. The tree of life is a family tree of organisms that describes the genealogical relationships among species with a single ancestral species at its base. Linnaean Taxonomy Taxonomy is the effort to name and classify organisms. In Linnaeus’taxonomic system for classifying organisms, each organism is given a unique two-part scientific name consisting of the genus and the species. 1. Agenus is made up of a closely related group of species. 2. Aspecies is made up of individuals that regularly breed together or have characteristics that are distinct from those of other species. Taxonomic Levels Linnaeus’system is hierarchical with nested taxa. The taxonomic levels from least to most specific are as follows: kingdom (Animalia) phylum (Chordata) class (Mammalia) order (Primates) family (Hominidae) genus (Homo) species (Homo sapiens) How Many Kingdoms Are There? Linnaeus proposed just two kingdoms—plants and animals. However, not all organisms fall neatly into these categories. An alternative five-kingdom system was proposed in the 1960s. Kingdom Monera Kingdom Protista Kingdom Plantae Kingdom Fungi Kingdom Animalia The Origin of the Phylogenic Tree of Life Carl Woese and colleagues studied small subunit rRNA, as a means for understanding the evolutionary relationships among organisms. 1. rRNAsequences should be very similar in closely related organisms but less similar in organisms that are less closely related. 2. Aphylogenetic tree reflects these relationships among species. Branches that are close to one another represent species that are closely related; branches that are farther apart represent species that are more distantly related. Changes to the Tree of Life The tree of life indicates three major groups of organisms: the eukaryotes • Eukarya and two groups of prokaryotes • Bacteria andArchaea. Therefore, Woese created a new taxonomic level called the domain, consisting of Bacteria,Archaea, and Eukarya. The location of certain branches on the tree is hotly debated and the shape of the tree will continue to change as databases expand. Why Do Giraffes Have Long Necks? Biologists test ideas about the way the natural world works by testing the predictions made by alternative hypotheses using carefully designed experiments. Simmons and Scheepers tested the food competition hypothesis that giraffes evolved long necks by natural selection because those with long necks reach food unavailable to others mammals. The Food Competition Hypothesis Predictions: • Neck length is variable among giraffes • Neck length in giraffes is heritable • Giraffes feed high in trees One of the three predictions of the food competition hypothesis—giraffes feed high in trees—does not hold true. Thus, there may be better alternative hypotheses to explain neck length in giraffes. An alternative hypothesis is that giraffe evolved long necks because longer-necked males win more fights than shorter-necked giraffes, and can then father more offspring. Data support this hypothesis. Class Notes: Eukaryotes have nucleus. Hybrids Amule does not have same number of chromosomes because parents do not share the same number of chromosomes.
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