Introduction to Natural Science 2007 Name (Print):__________________________________ Biology Exam II 1. Sickle-cell anemia is a genetic disease caused by a mutation in the β-globin gene. Individuals who are homozygous recessive for this mutation have red blood cells that readily collapse when deoxygenated; these individuals generally die from the genetic defect. Those who are heterozygous for this condition have an intermediate phenotype and can live with the defect. Interestingly, the malaria parasite cannot survive within these individuals or those with severe sickle-cell anemia. A. Compare the two images on the right and describe what evolutionary force is at work and why. Use specific vocabulary in your description. The images on the right show that Malaria distribution correlates with populations that have the sickle cell allele. Normally the sickle cell allele would be purified from a population because those individuals possessing the sickle cell allele would be less fit. However, when malaria is present in a population that has the sickle cell allele, those individuals who are heterozygous for the mutated allele are selected for because they are more fit – they are resistant to malaria. So, natural selection is the evolutionary force and heterozygote advantage is the outcome. B. If 9% of an African population is born with this severe form of sickle-cell anemia, what percentage of the population will be resistant to malaria but not suffer from sickle-cell anemia? Show your work. 0.9 = q2; take the square root for q = 0.3; solve for p using p = 1-q or p = 0.7 Those resistant to malaria but do not suffer from sickle-cell anemia are the heterozygotes, so solve for 2pq! 2pq = (0.3)(0.7) + (0.3)(0.7) = 0.42 or 42% 2. Four-o’-clocks produce flowers that are white (recessive), purple (dominant) or an intermediate color, lavender. In a large population that undergoes random mating, what allele frequencies will generate twice as many white flowers compared to lavender flowers? Show your work. There are many ways to solve this problem; I have given you two below. One thing to note is that the population is not necessarily in Hardy Weinburg equilibrium, but you could set it to HW equilibrium to solve it. Method 1: For the equation p2 + 2pq + q2 = 1, set q2 to 0.5 and 2pq to 0.25 (thus p2 is also 0.25 for it to add up to one) and solve for p using p = 0.25 + ½(0.25) = 0.375 and then for q using q = 1-p. This works out to be 0.625 and the alleles are not in HW equilibrium. Method 2: There are twice as many recessive (q2) flowers as lavender (2pq) flowers so the equation is as follows: x + x + 2x = 1.0; solving for x gives you: 4x = 1.0, x = 0.25; then plug the number back into the equation to solve for each allele. Malaria Distribution(in black)Sickle Cell Distribution(shades of grays)Malaria Distribution(in black)Sickle Cell Distribution(shades of grays)3. Early dog breeders were interested in creating a greyhound dog with the greatest speed. They carefully selected from a group of hounds those who ran the fastest. From their offspring, the greyhound breeders again selected those dogs that ran the fastest. By continuing this selection for dogs who ran faster than most of the hound dog population, they gradually produced a dog who could run up to 64km/h (40mph). A. On the left, draw a graph corresponding to the time during selection and clearly indicate where there is high fitness. B. On the right, draw a graph corresponding to the time after selection. 4. In a species of African butterfly, Pseudacraea eurytus, wing colorations range from a reddish yellow to blue. In both cases, these extremes of color from different ends of the spectrum look like (mimic) other species of butterflies that are not normally the prey of other the local predator group of birds and insects. Those butterflies that are moderate in coloration are eaten in far greater numbers that those at the extremes of the color spectrum. A. On the left, draw a graph corresponding to the time during selection and clearly indicate where there is high fitness. B. On the right, draw a graph corresponding to the time after selection. 5. Describe in your own words why sexual dimorphism exists. Provide an example. Sexual dimorphism exists due to sexual selection. One sex needs to attract mates or fight for mates. As a result the traits that allow them to attract more mates or fight better for mates are selected for in a population. Extreme traits between males and females are the result. There are many examples of this. Elephant seal males are much larger than the females because they must fight other males for territories. Male birds have more colors and are much brighter colored than females because females select males based on the intensities of their coloring. They do this because it is associated with a fitter male. Value of the Trait “Speed”Percentage of dogsValue of the Trait “Speed”Percentage of dogsHigh fitnessValue of the Trait “Speed”Percentage of dogsValue of the Trait “Speed”Percentage of dogsValue of the Trait “Speed”Percentage of dogsValue of the Trait “Speed”Percentage of dogsValue of the Trait “Speed”Percentage of dogsValue of the Trait “Speed”Percentage of dogsHigh fitnessValue of the Trait “Color”Number of IndividualsValue of the Trait “Color”Number of IndividualsHigh fitnessHigh fitnessValue of the Trait “Color”Number of IndividualsValue of the Trait “Color”Number of IndividualsValue of the Trait “Color”Number of IndividualsValue of the Trait “Color”Number of IndividualsValue of the Trait “Color”Number of IndividualsValue of the Trait “Color”Number of IndividualsHigh fitnessHigh fitness6. Hawaiian Drosophila show remarkable patterns of speciation. There are hundreds of species of Drosophilids on the Hawaiian islands and most are endemic (found only in one location/island). Some traits include: large body sizes, dramatic "picture wings", and "hammer-head" shaped heads. Phylogenetic studies show that flies on each sequential islands are related to species on nearby islands (i.e., flies on Hawaii are derived from ancestors on Maui and so on - indicated by the dashed arrows). A. The events described above are indicated by the process “A” in the drawing on the right. Please describe the specific type of speciation event that has occurred and discuss the possible evolutionary forces involved.