Evolutionary Biology BIOL 3350 Dr Lisa Rapaport Lecture 8 Part 2 Lecture 9 Agents of Evolution Mutations I Maintenance of a Deleterious Mutation Sickle Cell Anemia A Changing this one amino acid changes the structure of the molecules and makes it less able to carry as much oxygen B The symptoms of sickle cell anemia are very severe people with this disease get swelling of the joints jaundice out of breath frequently C These are codominant alleles D HBS sickle cells E Typically a change in allele frequency suggests a change in the environment that now favors this allele F Hbs homozygotes exhibit sickle cell anemia G Hbs heterozygotes may have no or very mild symptoms also have resistance to malaria overdominance 1 Heterozygotes for this trait are favored in both aspects lesser sickle cell symptoms and malaria resistance 1 I II III IV V Agents of Evolution Migration Migration gene flow A The addition of these new alleles can cause deviation from HWE B Migration is another force of evolutionary change as it has the ability to cause allele frequencies in a population C Migration involves incorporation of new genes into a receiving population changes in allele frequencies in both populations can result due to this gene exchange Integration of migrant alleles A Migration can act to conserve genetic variation can increases the frequency of rare alleles for example B Migration can increase the frequencies of rare alleles at much faster rates than mutation can thus evolution can occur at a much faster rate by increasing this variability C Migration greatly increases the genetic variability of the receiving population Genetic results of migration A Homogenizes the variability between the 2 different populations makes the 2 different populations more similar to each other but increases the variability in each individual population If you mix 2 very genetically different populations with one another their allele frequencies will eventually converge and become very similar to one another B C The genomes of both populations becomes more variant D Mixing 2 genetically different populations causes both populations to deviate away from HWE E Migration can cause evolutionary change After migration stops A After migration stops it takes 1 generation for the population to return to HWE again the population has to be relatively large random mating has to occur Example of interaction of selection and migration Lake Erie Water Snakes A These snakes are non venomous and very small many different patterns and solids great variation in their banding patterns phenotypes B This is a codominant situation plain and heavily banded are homozygous a medium amount of banding is heterozygous C These snakes live in Canada on the mainland in the United States on the mainland and on many islands D Almost all of the individuals on the mainlands are banded and most of the snakes on the islands are plain E Morphtypes 1 The intermediate patterns are heterozygous A1A2 2 The heavy banding A1A1 is homozygous 2 3 Plain A2A2 is homozygous F Baby snakes have a more definitive pattern or lack of pattern G These are water snakes so they move from one area to another very easily one population H Island hoping is common so all island snakes are grouped together as I Banded D is the most common in the mainlands of Canada and the United States there are small variation amounts of intermediate banding and plain snakes in the United States Islands that are close to the mainland share more similarities with the mainland than the islands that are farther from the mainland J K These differences in phenotypes are due to the very different habitats on the islands verses the habitats on the mainlands L On the sandy soils of the islands the plain snakes survived much better than the banded snakes M On the mainland the banded snakes survived much better than the plain snakes N Islands favor the plain pattern mainlands favor the banded patterns O Graph 1 x axis frequency of A2 allele 2 y axis change in the A2 allele 3 Equilibrium is reached when it crosses the line 4 When migration is really high and there is not much selection the frequency of the A2 allele decreases 3