BIOL 1050 1st Edition Lecture 24 Outline of Last LectureI. Mechanisms of Evolutiona. Natural selection Outline of Current LectureI. SpeciesII. SpeciationIII. Phylogenies and classificationIV. Diversity Current LectureI. Species i. Biological species concept: species are populations of organisms that could interbreed with each other but cannot interbreed with other organisms1. Cannot be applied in all situations (e.g. with fossils and asexual organisms)2. Even if they can be produced in captivity, organisms that do not naturally occur in the wild- such as the “liger”- are not considered species3. Relies on ability to reproduce, not similarity in appearanceii. Reproductive barriers between species1. If individuals of 2 different species try to mate, no fertile offspring will be produced2. Barriers block exchange of genes between species and allow them to evolve independently3. Barriers keep species reproductively isolated from each othera. Prezygotic barriersi. Individuals are physically unable to mate with each other orii. If individuals are able to mate, the male’s reproductive cell is unable to fertilize the females reproductive cellb. Postzygotic barriersi. Matings produce hybrid individuals that do not survive long after fertilization orThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.ii. If hybrid offspring survives, they are infertile or have reduced fertilityiii. A mule results from the mating of a horse and a donkey1. Females horses have 32 chromosomes, male donkey has 31 chromosomesa. Mule has 63, always too many or too few chromosomes to reproduceII. Speciationa. Speciation: is the evolution of one or more species from an ancestral formb. 2 forms:i. Allopatric speciation: when 2 populations are geographically separated1. Initial population 2. Reproductive isolation: suppose a river forms through the squirrels habitat, separating the population, because the cannot cross the rive they are reproductively isolated3. Genetic divergence: over time the populations on either side diverge enough genetically that they are no longer able to interbreedii. Sympatric speciation: without geographic isolation1. Polyploidy a. During cell division, an error occurs in which chromosomes are duplicated but the cell does not divide. This creates a gamete with twice as many sets of chromosomes as a gamete of the parent from which it cameb. A gamete with two sets of chromosomes cannot produce offspring by fertilizing a gamete with one set of chromosomesc. A gamete with two sets of chromosomes can, however produce offspring by fertilizing another gamete with two setsof chromosomes, producing an individual with four sets of chromosomesd. The new individual has achieved instant reproductive isolation from the original population and therefore is considered a new species 2. Allopolyploidya. Two plants from a different but closely related species interbreed, forming a hybridb. The hybrid may no longer be able to interbreed with either of the parental speciesc. The hybrid may however, be able to propagate itself asexually as many plants cand. The hybrid individual has achieved reproductive isolation from the original parental population and, therefore is considered a new speciesIII. Phylogenies and classificationa. Naming speciesi. In the mid-1700s Linnaeus created the naming system still used todayii. Phylogeny 1. Systematists name a species and determine where it fits in tree of life based on its evolutionary history (its phylogeny)b. Evolutionary treesi. The branches of an evolutionary tree can be spun around the point at which they are split and still remain accurateii. Evolutionary trees do not show which groups are more primitive or advanced, just which groups are more closely related to which other groupsiii. An evolutionary tree with a branch for each of the millions of species on earth would be incredibly complexiv. Trees can be constructed using anatomical data or DNA datav. DNA evidence separates homologous structures based on convergenceIV. Diversitya. Bacteria and archaeai. Unicellularii. Prokaryotesiii. Believed to be ancientiv. Also called microorganisms or microbesb. Eukaryai. Includes protists plants, fungi and animals1. Protistsa. Are all eukaryotesb. Animal likec. Fungus liked. Plant likee. Shift to multicellularityi. The shift to multicellularity occurred in the protistsii. Increased complexity, made more variation possibleiii. Allowed for increasing diversity2. Plantsa. Multicellular eukaryotes that can make their own food by photosynthesis3. Fungia. Eukaryotes, mostly multicellularb. More closely related to animals than plantsc. Digest food externally and absorb