Lecture 22Outline of Last Lecture I. Genetic Variation Continued a. Hardy Weinberg Equilibrium Outline of Current Lecture II. Natural Selection a. Types of Selection for Phenotypes III. Other Mechanisms a. Gene Flow b. Genetic Drift Current Lecture Evolution IV Mechanisms: Natural Selection and Genetic Drift Natural Selection -result of evolution driven by natural selection is that populations become better adapted to their environment -only evolutionary change that can lead to adaptation -example: fur coat color studied in rock mice who live in Arizona and New Mexico -found that the mice that live in the black rock areas tended to have black fur. The ones on the white rocks tended to be white or yellow. Can see the evolutionary advantage (black blend into black rock, white blend into light rock) -gene found in lots of mammals, code for hair that have alternation of different colors -dark mice have four mutations leading to proteins not working causing melanin to be produced (how selection works on a particular allele to cause a change) Positive Selection Leading to Trait Fixation -positive selection is when a trait is selected for -usually will lead to “fixation” of a trait (when all of the population has the trait, therefore it will no longer be subject to natural selection because it is the only trait in the population) Bio 152 1st EditionThese 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. !Edited with the trial version of Foxit Advanced PDF EditorTo remove this notice, visit:www.foxitsoftware.com/shopping-negative selection is against -in either case the alleles will NOT be in Hardy-Weinberg equilibrium **Clicker Question** Data show the birthweight of babies in blue and percent mortality as a red dot. How would you describe this kind of selection? -keeps babies at around 3 kg (has a particular name that we will be told later) What do you predict about the genetic basis of this trait? -The trait is probably caused by the interaction of many genes -if you’re not told which gene controls what, there are very few traits that can be quantified by a single gene -birthweight is very complex and due to many factors like length of bones etc. **like the whisker question on last week’s quiz** Three types of selection for phenotypes/traits: -stabilizing selection tends to reinforce a median trait, this is the majority form -gets rid of the outliers -directional pushes to one extreme or another -gets rid of the lighter mice, for example -pushes the median in one direction or another -disruptive selection tends to split the phenotype—this can lead to speciation -the mean is selected against So which kind were seen in the previous question about birth weights? -stabilizing -not selection for or against a trait (that would be positive or negative), selection on a distribution of traits (not plus or minus) **Clicker Question** There are some genes that help a person resist the Black Death. Rare in indian populations, common in Roma people (Roma are a european population). So which selection might account for this? -positive selection -in a population of people that migrated to Europe, some would have this gene and some wouldn’t. Those who didn’t have the gene would die because they would be vulnerable to the Black Death, but those who did would survive. -allele present in India but at a very low level because it is in Hardy-Weinberg equilibrium, there is no selection for or against it — there is once the population moves to Europe Galapagos Finches — drought caused only larger seeds. What sort of selection is this on the finches? -the distribution goes from centered around 8.9 to 9.8, do directional selection Result of these types of selection = convergent evolution-organisms that don’t share common ancestors recently but they live in similar environments/niches and look very morphologically similar -when a new trait evolves in two different yet similar populations — can’t have shared the trait earlier on so its not an ancestral trait -example = having fur isn’t convergent evolution because the ancestors did have it. **Clicker Question** Is the bat wing and bird wing an example of convergent evolution? (bats come from mammals, birds come from dinosaurs). -Yes : bats evolved from land mammals without flight, and birds evolved from dinosaurs that didn’t fly, so the wing evolved separately and allowed both of these organisms to fly -the structure the ulna and phalanges are ancestral trait (so the bone structure is an ancestral trait but the wing itself is convergent evolution) TAKE HOMES Other mechanisms like Gene Flow and Genetic Drift **Clicker Question** Parus major, a bird in Europe on an island off the coast of Netherlands. Eastern population is considerably larger than the western. What might explain this? -C and D are not relevant, and also there is no data shown for them -B is the correct answer -this island has very different ecology from the mainland — because of this certain traits are selected for. But in the central region of the island lots of mainland birds come over and dilute the gene pool. So rather than having selection for traits that allow birds to live well on the island you have less selection because of lots of birds coming from mainland. The eastern population is larger because it has less gene flow (less genes coming in) -gene flow causing maladaptation instead of adaptation (bad for the population) Gene Flow: have purple and yellow flower population, if pollen from purple flower goes into yellow flower population, then you might start seeing some purple in the yellow population -can come from migration -pollen movement (in the case of plants) -it can be positive, negative, or neutral -evolution can occur because of gene flow **Clicker Question** Gene flow may do which of the following? -ALL OF THEM -it can introduce alleles that improves fitness — it can introduce an allele that can be selected for but in and of itself it cannot be selectedGenetic Drift 96 populations of 8 fruit flies each with 0.5 frequency for forked and unforced hair allele. Neither allele has any selective advantage. Each generation; 4 males and 4 females from each vial were selected to start the next generation. 16 gens later, what would you expect to see in these vials? -you only took 4 males and 4 females. If you