Biology 203 1st Edition Lecture 5Outline of Last Lecture I. How do biologists define a species?II.PhylogenyIII. Homoplasious vs. Homologous charactersOutline of Current Lecture I. PhylogenyII. Using DNA sequences to create a phylogenetic treeIII. Molecular ClocksIV. FossilizationCurrent LectureI. Phylogenya. The oldest split is when the ancestors of lungfish split from the ancestors of the tetrapodsb. If you sequence several individuals, members of the same species should form a monophyletic group, a cladec. Example: Praticolellagriseolai. Taxonomy based on shell morphology – largely on banding patternii. We assumed they were all one, invasive speciesiii. However, we found Praticolellagriseola in several distant branches on a molecular tree of the genusiv. We have now named two different species and are working on a thirdv. Take home message: the names of organisms matter, and they change as we learn more about biodiversityII. Using DNA sequences to create a phylogenetic treea. By utilizing DNA sequences, we can now make phylogenetic trees and estimate the time the lineages divergedb. The closer the DNA sequence is to the outgroup (most common ancestor), the earlier it split off.c. The more different the DNA sequence is, the later it evolved.III. Molecular Clocksa. Basic assumption of molecular clocks: changes in sequence accumulate at equal rates over time (generations)These 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.b. Need to consider the following when using molecular clocks:i. Whether your DNA regions are synonymous or non-synonymousii. Different taxa have clocks that tick at different rates (ex: elephants have different generation times than mice)iii. Different genes change at different ratesiv. Can’t reliably determine timing from molecular data alone!c. Molecular data must be calibrated to be used as a molecular clocki. If we assume a constant rate of change in this genetic region and know from the fossil record that organism A diverged from the rest 2MYA and organisms C and Ediverged .5MYA, what would be the estimated timing of divergence between B and D?ii. Calibrate using the fossil record (or other molecular clocks) to set the “Time” scaled. How do we estimate the timing of species divergence?i. Molecular Clocksii. Fossils – where are they stratigraphically, radiometric dating of isotopesIV. Fossilization: The processa. A tree lives in a swampy habitat. The tree drops leaves, pollen, and seeds into the mud, where decomposition is slow.b. The tree falls. The trunk and branches break up as they rot.c. Flooding brings in sand and mud, burying the remains of the treed. Over many years, the mountains erode and the swamp is filled with sediment. The habitat dies.e. Eventually, enough material builds up to preserve the organismf. Problems with fossils:i. Most organisms are not fossilizedii. Only the hard parts of organisms are fossilizediii. Habitat bias – only organisms near water and sediments can be fossilizediv. Recent fossils are more common than more ancient onesv. Highly non-random – fossilization is unlikely so it is mostly the common species that are