Copy of Lab 2 - HWEQ Modeling a Population

.docx

School

Arizona State University *

*We aren’t endorsed by this school

Course

182

Subject

Biology

Date

Jun 1, 2024

Type

docx

Pages

Uploaded by asilvazSx

Modeling a Population How do factors such as gene flow , natural selection and genetic drift affect a population of organisms? You’re going to be answering these questions by working on a model set of organisms: gem beetles. The gem beetles are represented here by different colored plastic beads. These particular gem beetles can exist in one of three color phenotypes: red, pink, or white. The red gem beetles (AA) are homozygous for the ‘A’ allele, the white beetles (aa) are homozygous for the ‘a’ allele, and the pink gem beetles (Aa) are heterozygous for the two alleles. Color in gem beetles is an example of incomplete dominance, since the heterozygous phenotype is different from either of the homozygotes. Gem beetles normally live in environments found on islands (replicated around the room, at different tables). On each island, the environment varies according to the geographical location. N side: RED BANDANA S side: GREEN E side: BLACK AND WHITE W side: PINK AND WHITE DOTS. I. CREATING THE EQUILIBRIUM POPULATION – Gene Pool of the Original Population Let’s study the starting gene pool of the gem beetle population on your island. You will be working primarily at one of the four environments, on one island. Table 2 indicates the number of gem beetles of each color that you should add to your assigned environment at your island. Add a total of 100 gem beetles to your environment, indicated in table 2. Be sure to spread them around and mix them up within that environment. Table 2. Original gene pools of the gem beetle populations at each geographic location on an island. Location # Red (AA) # Pink (Aa) # White (aa) Total # (N) Total ALLELES North (Red Bandana) 25 50 25 100 200 South (Green) 49 42 9 100 200 East (Black and White) 4 32 64 100 200 West (Pink and White dots) 25 50 25 100 200 Note the differing initial number of the red, pink, and white gem beetles varies at the different locations on the island. Since the color of the gem beetles is an example of incomplete dominance, the genotype and phenotype frequencies are the same. 1. Based on the # of individuals of each genotype, and the total # of individuals, calculate:

a) the frequencies for each genotype: AA, Aa, and aa (write in Table 3 below) b) the population-level allele frequencies ( p and q ). (also write in Table 3 below) If we leave these gem beetles alone they will (hopefully) survive, and reproduce. You should recognize that each environment’s gene pool is currently a closed population, and the probability of two gem beetles mating is only related to their frequency in the population. Right now, there is no immigration/emigration, or natural selection. 2. Calculate the expected genotype frequencies of the offspring (next) generation of your population (table 3). How do you do this? You use your parental allele frequencies to construct a population-level Punnett Square in the space provided, which gives you expected genotype frequencies in the next generation. Record these expected genotype frequencies in Table 3. Table 3 . Genotype/phenotype and allele frequencies for your initial gem beetle population, in your environment. Genotype/Phenotype FREQUENCIES Allele FREQUENCIES Red (AA) Pink (Aa) White (aa) ‘A’ allele ( p ) ‘a’ allele ( q ) Parental (initial) frequencies 0.25 0.50 0.25 0.5 0.5 Offspring (next) frequencies P^2 0.25 2pq 0.5 Q^2 0.25 YOUR STUDY SITE (Geographic location): North 3. Is your population in Hardy-Weinberg equilibrium? Explain your answer. Our population is in Hard-Weinberg equilibrium because nothing has changed. II. EFFECTS OF GENE FLOW Spring has come to your island, and the reproductively mature gem beetles are anxious to find a mate. The gem beetles at the four geographic locations on your island tend to behave somewhat differently during mating season. The gem beetles on the north and south sides of the islands are homebodies. They find a neighborhood male or

female they are compatible with and mate. However, the gem beetles living on the east and west sides of the island are more restless. Some of these gem beetles leave their native population to find a mate. Due to the presence of mountain ranges on the island, gem beetles from the EAST shore can only migrate to the SOUTH, and gem beetles from the WEST shore can only migrate to the NORTH shore. This annual mating migration results in gene flow among the populations in each island. Gem beetles are emigrating away from the eastern and western sides and immigrating to the southern and northern sites, respectively. We are now violating one of the basic assumptions of the Hardy-Weinberg principle. Now try to determine the impact of this gene flow on your original population’s genetics. Make a prediction – Look at the population on your environment, and also at the population on the other environment that is either immigrating or emigrating with yours. What do you expect to happen to your population’s genotypes, after migration has occurred? Increase (+), decrease (-), or stay the same (0). Genotype Frequency Predicted Result after Gene Flow AA: 0 Aa: + aa: - If your study population is either on the EAST or WEST side, some of your gem beetles will now migrate (east to south, west to north). RANDOMLY remove (mix your beetles, close your eyes and grab) 15 gem beetles from your environment. Give these emigrants to one of the researchers at the destination environment on your island. At this point, each location should have either lost or gained some gem beetles through emigration or immigration. Complete table 4 and calculate the new numbers of each genotype/phenotype in the population. Table 4 . NUMBER of gem beetles of each color before and after gene flow. Red (#AA) Pink (#Aa) White (#aa) Total # (N) Total Alleles Starting population, before gene flow (from table 2) 25 50 25 100 Number added or removed 5 5 5 15 New population, after gene flow 30 55 30 115 230 Complete table 5 to show the effect of gene flow on your population. The Initial population values and allele frequencies for row 1 of this table come from table 3. In the second row of Table 5, calculate the genotype/phenotype frequencies in your new population after gene flow, and then the new allele frequencies. Table 5 . FREQUENCIES of genotype/phenotype and allele for your gem beetle population before and after gene flow. Genotype/Phenotype FREQUENCIES Allele FREQUENCIES Red (AA) Pink (Aa) White (aa) ‘A’ allele ( p ) ‘a’ allele ( q ) Starting population, before gene flow (from table 3, row 1) 0.25 0.50 0.25 0.5 0.5

New population, after gene flow 0.26 0.478 0.26 0.5 0.5 Next generation , after reproduction P^2 0.25 2pq 0.50 Q^2 0.25 Use the allele frequencies (above) to calculate the Next generation’s genotype frequencies (at left) Difference between Starting population and Next generation (absolute value) 0 0 0 Sum of differences: 0 Recall that your initial population was in Hardy-Weinberg equilibrium. Is your population still in Hardy-Weinberg equilibrium? To answer this question, compare the starting population to the next generation’s genotype/phenotype frequencies in table 5. If they are IDENTICAL (or nearly so), the population is still in Hardy-Weinberg equilibrium. If they are not, the population is no longer in Hardy-Weinberg equilibrium . It is evolving! QUESTIONS: a) Drawing a conclusion – How did your predictions of what would happen to your population after gene flow compare to the actual results you found? - My prediction was a change happening to my population after gene flow being false compared to the actual results I found which were no differences happening due to the same population numbers of WEST and NORTH. b) Which populations on your island (if any) are still in Hardy-Weinberg equilibrium? Is there a difference between the populations that emigrated (lost beetles), and the ones that had immigrants (gained beetles)? - Both islands are in Hardy-Weinberg equilibrium. They both started with the same population therefore there is no difference after migration. c) While gene flow can cause evolution in populations, in what circumstances does gene flow NOT cause evolution in a population? - Gene flow does not cause evolution to a population when everything stays the same. III. EFFECTS OF NATURAL SELECTION In the absence of unusual environmental changes, the major factor affecting the survival of gem beetles is predation. The major predator of the gem beetles is the ravenous finch (you). You look for gem beetles in their environment and pick them up, one at a time, with a pair of forceps (meant to simulate your beak pecking at them, which would happen one at a time). The ability of the ravenous finch to successfully prey upon the gem beetles depends on both the color of the gem beetles and its environment.

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version