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69 Cards in this Set
- Front
- Back
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Speciation |
Divergence of one lineage into two or more over time. |
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3 Key Steps of Speciation |
1. Isolation (restricted gene flow) 2. Divergence of population 3. Reproductive isolation (pre and post) |
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Speciation is a ________. |
GRADIENT |
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What does it mean for species to be Allopatric? |
Lineages are in different places. |
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Examples of Divergence Mechanisms (4) |
Genetic drift, mutation, natural and sexual selection. |
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Reproductive isolation could be the _____ or a ______ of divergence, or evolve after secondary contact (reinforcement). |
cause; by-product |
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How does reproductive isolate reinforce speciation? |
If there is some divergence/isolation, but still some hybridization going on then often sexual selection will often be the finishing blow to split the two groups into different species. It makes the species more distinct to the point of differentiation. |
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3 Kinds of Sympatric Splits |
1. Ecological
2. Temporal 3. Behavioral |
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Sympatric species are... |
in the same physical location. |
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Since sympatric species are in the same place, what do they require for speciation? |
Strong natural or sexual selection coupled with assortive mating. |
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Do pre or post zygotic mechanisms pop up first for reproductive isolation? |
Pre seem to come first. (often won't mate in the field even if when you mix sperm and egg in the lab you could get a viable hybrid) |
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Three Postulates of Natural Selection |
IF 1. Population contains variation 2. Some of that variation is heritable 3. And survival and reproduction are non-random. THEN: Evolution by natural selection. |
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Levels of selection range from... |
individual genes to whole genus. |
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To be a level of selection, each level must have |
variation, heritability, and ability to reproduce (fitness). Each level has different strengths of these postulates though, and different strengths means different strengths of evolution. |
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Genetic Selection: Segregation Distorters |
Organisms that have alleles to manipulate meiosis to cause their output to be bias towards one allele or another. Might cause one allele to fail or that chromosome to not be able to be used. Result: lots of the other allele. |
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Segregation Distorters: Drosophila (conflict between gene and individual level) |
Found in stocks in Cali and Wisconsin. About 90% of offspring from +/sd heterozygote males have the segregation distorter allele (sd). The allele segregations normally in females. Heterozygous males have decreased fertility by about 50% though!! Ingeneral, segregation distorter genes are actually tightly linked loci. There isusually a recognition locus and a distorter locus. The distorter alleleproduces a protein that binds to the recognition sequence. If the sequence isthe "distorter" version, there is no effect. If it is anothersequence, it prevents the chromosome from entering the sperm. |
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Individuals are hierarchies of... |
replicators. |
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Organisms experience ________ selection. |
multilevel |
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Organelle Selection: Two Level Selection |
Outer circles = higher level (whole cell)
Inner circles = lower level (mitochondria) |
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Organelle Selection |
Even split Big A makes more Big A is better at getting into cell |
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Why do mitochondria have their own selection? |
They replicate separately from the cell. |
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If A and a replicate at the same rate and are equally distributed among daughter cells at cell division, is selection occurring at the mitochondrial level? |
No; no variation, no room for selection. |
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If A replicates faster than a, is selection occurring at the mitochondrial level? |
Yes! |
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Is there potential genomic conflict if A replicates faster than a on the mitochondrial level? |
If A is higher fitness to cell, no. If a is higher fitness to cell, yes. |
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Organelle Selection Example: Petite Yeast Mutants |
Petite mutants have lost large chunks of the mitochondrial DNA and can replicate faster, but they needed this DNA so they are worse at cellular respiration. However, they can outcompete the wild type mitochondria. Yeastcells that have only these mutant mitochondria can no longer respire and are ata fitness disadvantage compared to other yeast cells. Selectionshould be more efficient in large populations than small. |
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Organelle Selection Example: Petite Yeast Mutants Experiment (set up, results, conclusion) |
Started with yeast with both kinds of mitochondria. Started with small, med, and large population sizes and let them evolve for 150 generations. Results: Petite mutants most common in small populations, some in medium populations, and almost none in large populations. Conclusion: Genetic drift is strong is small population (allows less fit mitochondria to thrive), while selection takes over in large population (the better fitness mitochondria is selected for). |
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What is a good example of cellular selection? |
Cancer. |
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Why is group selection controversial? |
Often used as a "for the good of the species" argument. |
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Why can't we argue individuals do things for the good of the species? |
This idea is too susceptible to cheaters. |
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How do we demonstrate group selection does exist then? |
We must show a conflict between individual and group pressures and that the phenotype fits better with group pressure. |
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Group Selection: Beetle Experiment |
Different beetle groups in same size containers and ran them for 8 generations.
Favored groups that produced the higher colony densities in one line. Favored groups with lowest colony density in other line. Third line was control. Bychoosing entire groups Wadewas selecting a group that had the ensemble of geneticattributes that were conducive to self-limiting behaviors (less fighting and less cannibalism). Results: What he selected for is what he saw (dense line had most dense colonies (less cannibalism) and empty line was much less dense (more cannibalism)). Conclusion: Looks like they are doing it for the benefit of the group, but really it is just showing that group selection can happen. |
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Is group selection generally weaker or stronger than individual selection? |
Much weaker even in artificial situations.
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Why is group selection weaker? What is it about group traits that makes them less responsive to selection? |
1. Groups heritability is not very good (a new individual can easily change the group). 2. Variation needs to be heritable and this is not very common/strong. 3. Group traits are less related to fitness than individual traits (related to graph; trait vs. fitness; neat line for individual but perhaps less correlated for the group trait). |
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In order for group selection to work do we want big or small groups? |
Small |
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In order for group selection to work do we want fast or slow group generation time? |
Fast |
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In order for group selection to work do we want lots of variability or limited variability? |
Lots of variability |
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Group Selection: HIV Transmission - What is the dilemma? |
Only some many host cells available in an organism. HIVs that quickly blow through host cells are the ones that do best (most likely to survive and pass on), but going too quickly as a group is like to kill host before transmission can occur. |
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Virulence vs. Fitness Curve shape for HIV virions as an individual? Curve shape for all HIV virions in a host (as a group)? What about as a group with lots or contact vs. little contact? |
Individual: positive slope (some cap, but rises for a long time first) Group: bell curve (needs a certain level of virulence to take, but can't kill the host before getting contact with next host; sweet spot somewhere in the middle where it can get passed on but won't kill host too quickly). When there are few new contacts, it is better for the group to be much less virulent to wait it out for a new host whereas when there are often new contacts they can be more virulent and move along quicker. |
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Can host affect HIV virulence sweet spot? |
Yes! If they have a lot of safe sex, the virulence will favor less virulence because HIV needs the host to survive longer to pass on to another host. |
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Lineage Sorting: Antelope Speciation
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Diverged many years ago: Only a few kinds of impalas (plainer), but many kinds of gnus and hartebeests with much variation and ornamentation. |
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Why are there more than 300,000 species of beetles and only 9 kinds of horseshoe crabs despite both popping up on the planet around the same time? |
Their lineages differ in tendency to diversify. (they have different characteristics) |
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What kind of tendencies cause a species to diversify a lot? (3) |
High mutation rates, potential for big rearrangements in the body (hox genes; segments can be moved around and still function especially in insects), push for specialization. (all characteristics that also often lead to extinction) |
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Paleontology |
The record of past life derived from geological and biological evidence. |
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What does paleontology allow us to do? |
It allows us to view speciation and extinction over much longer periods of time than is possible in our lifetimes. |
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Fossils: Radiometric Dating |
Rocks contain radioactive isotopes. Radioactive decay (change from parent to daughter state) is constant and not affected by the environment. We can measure the level of decay and use it to determine how old the rock is. |
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How old does radiometric dating estimate the age of the earth to be? |
4.56 billion years old |
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Different elements allow us to date back to... |
different levels of time. |
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How can we ensure our radiometric dating measurements are accurate? |
We can compare the decays of different elements in the same rock to get an average dating of the rock. |
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3 Kinds of Fossils |
1. Impressions 2. Permineralization 3. Unaltered remains |
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Permineralization |
Bone gets replaced by minerals over tens of thousands of years. (classic fossils) |
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Fossils |
Remnants of a biological thing that you can use to make inferences about the past. |
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What gets fossilized?
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Morphology (typically hard skeletal elements) and behavior (can be read from position and number of fossils). |
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How fine scale can morphology from fossils be? |
Very fine; as fine as contrast of colors on feathers that can fell us the bird had showy feathers like our modern birds do today. |
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Examples of Behaviors we can tell from Fossils and How we can tell Them
(3) |
What they ate (one fish sticking out of another), how they took care of young (front death near nest), size of heard (from footprints). |
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Fossil Strengths (3) |
1. Can see deep time (>3.4 bya) 2. Transitional fossils helps our understanding of evolution and phylogenetic trees (many intermediates are known) 3. We are interested in it! It is our history. |
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Oldest Fossil |
Cyanobacteria like stromatolites from more than 3.4 bya. |
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Human Interest |
Examples of Homos found |
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How old is the most recent homo specimen aged and what does this mean? |
13,000 years ago which means it co-existed with modern humans for perhaps 100,000 years! |
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Fossil Weaknesses (3) |
1. Bias - geographic, taxonomic, temporal 2. Species concept - we are constrained to morphospecies concept 3. Easy to misinterpret and the record is incomplete. |
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Geographic Bias of Fossils |
Most of our fossils are marine or from swamps because fossils form well there. Anaerobic marsh, ocean, and lake sediments are best for fossils. |
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Taxonomic Bias in Fossils |
Things with hard parts fossilize better (snails better than slugs). 80% of fossils are marine, but only 10% of extant species are marine. |
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Temporal Bias in Fossils |
Really old fossils may go back to the core and disintegrate; we see more recent fossils better/more often. |
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Cambrian Explosion |
When most of the species we see today showed up on the planet. |
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Biggest Mass Extinction we know of |
Permian Extinction |
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Dinosaur Extinction |
Cretaceous Extinction |
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If all of Earth's history was the semester where would the origin of life be? Note: First day was Jan 20 |
Feb 8 |
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Apoptosis and Group Selection |
Apoptosisoften invoked as example of group winning: Death of senescent individuals is said tobe advantageousto the population as a whole, sinceresources in short supply are saved, and to be of no conceivable selectiveadvantage or disadvantage to the individual since he is postreproductive at death. Most of the claims forthe operation of selection at the population level arise from what are perceived to be the self-regulatingproperties of population |
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Order the following events: multicellularity invasion of land, eukaryotes/sex birds evolve flights extinction of dinosaurs origins of humans invasion of land extinction of 83% marine genera cambrian explosion |
eukaryotes/sex multicellularity cambrian explosion invasion of land extinction of 83% marine genera birds evolve flight extinction dinosaurs origins of humans |
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Why is individual selection the strongest level of selection? |
Belowthe level of the individual, the replicating units are usually dependent on thesurvival of the organism Abovethe level of the individual, the characteristics that allow selection tooperate efficiently are absent |
