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Biology 110 – Survey of Biology

Lab Report

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Summer 201567163 4 UnitsNVC 2230MTWTh 12:20 PM – 4:20 PMRIDDELL

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Lab Assignment #: 4 Team Name:

Lab Assignment Title: Gene Frequency Hardy-Weinberg Date:

Background● Whether an allele is dominant or recessive does not have an effect on allele frequency within a population.● We know that the Hardy-Weinberg principle states that allele and genotype frequencies will remain constant over

different generations, given that there is an absence of other evolutionary influences (Reece).● The Hardy-Weinberg equilibrium can be applied to the population only if (Reece):

○ There are no mutations ○ Mating is totally random○ There are no selective pressures in play (predators, disease)○ Extremely large population size○ No gene flow (reproductive isolation)

● The Hardy-Weinberg equilibrium can be disturbed by a number of forces- including mutations, natural selection, nonrandom mating, genetic drift, or gene flow (Reece).

○ For instance, mutations disrupt the equilibrium of allele frequencies by introducing new genetic material into a population. Certain combinations of alleles may harm, help, or not effect an organism. This has an effect on the reproductive success of the organisms within the population. Harmful or helpful phenotypes result in either a directional or disruptive selection, changing the gene frequency. Neutral phenotypic mutations will result in a stabilizing selection, making the Hardy-Weinberg equilibrium still applicable.

○ Likewise, nonrandom mating (i.e. sexual selection) disrupts the Hardy-Weinberg equilibrium because this type of behavior typically encourages directional or disruptive selection, resulting in changes to the gene frequency.

○ Another factor that can upset this equilibrium is genetic drift, which occurs when allele frequencies grow higher or lower by chance and typically takes place in small populations.

○ Gene flow, which occurs when breeding between two populations transfers new alleles into a population, can also alter the gene frequency equilibrium.

○ Since all of these disruptive forces occur commonly in nature, the Hardy-Weinberg equilibrium rarely applies in reality; therefore, this principle describes an idealized state, and genetic variations in nature can be measured as changes from this equilibrium state.

● There are also Hardy-Weinberg formulas that allow scientists to determine whether evolution has occurred. ● Any changes to the gene frequency in the population over time can be detected.● The Hardy-Weinberg formulas allow us to detect allele frequencies that change from generation to generation,

thus allowing a simplified method of determining whether evolution is occurring. There are two formulas that are relevant:

○ p2 + 2pq + q2 = 1 ○ p + q = 1

■ p = frequency of the dominant allele in the population ■ q = frequency of the recessive allele in the population ■ p2 = percentage of homozygous dominant individuals■ q2 = percentage of homozygous recessive individuals ■ 2pq = percentage of heterozygous individuals

● By using these formulas we can determine whether or not a population is in the Hardy-Weinberg Equilibrium for a certain position.

○ If there is a significantly large difference between the known and calculated genotypic frequencies, then the population is not in the Hardy-Weinberg equilibrium due to at least one of the five conditions not being met.

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● This experiment will demonstrate that the allele frequencies will remain unchanged unless selective pressures act upon the population, and in the case of random mating; the frequencies of the genotypes will remain constant (there is no gene flow present).

● This experiment will help us understand the importance of multiple factors acting upon a population, such as natural selection, but will also demonstrate the limitations of the Hardy-Weinberg Equilibrium.

● For more information see: Hardy-Weinberg Equilibrium Model [Internet]. San Marcos: Palomar College; n.d. [cited 2015 Feb 24]. Available from: http://anthro.palomar.edu/synthetic/synth_2.htm

Purposes / Objectives:● To run a series of experiments under different conditions with controlled factors in an attempt to determine how

effective the Hardy-Weinberg equilibrium is in predicting allele frequency within actual populations found in nature.

● Comparing the results of running this experiment under different conditions will demonstrate more precisely what type of selection is favored by altering the independent variables (directional, disruptive, and stabilizing selection).

● To determine changes in allele frequency under different sets of environmental pressures.● To test the validity of the Hardy-Weinberg principle and to be able demonstrate this concept in a controlled

laboratory environment

Hypotheses:● The ratio of alleles within the first run (where all conditions of the Hardy-Weinberg equilibrium are met) will

remain constant; this acts as our control group.● The case consisting of two beneficial mutations along with a zero percent survival rate mutation will result in a

massive overpopulation within a couple generations because of the absence of predation. In terms of gene frequency, the alleles present in these two populations will quickly grow to represent a major proportion of the gene pool.

● The negative mutation trial where the mutations are either neutral or disadvantageous will result in a lowering of the general population due to a reduction in the number of individuals with the adverse mutation. Consequently, the neutral portion of the population will gradually reproduce to fill the vacancies left by the dead individuals, resulting in a constantly decreasing percentage of negative mutation individuals.

Subject(s) / Specimen(s):● Beads of multiple colors

Materials:● Plastic cups● Paper● Writing instrumentation

Methods:● Starting populations of 50 individuals represented by 100 alleles (beads) were picked out of the cup at random;

this essentially signifies random mating.● The genotypes of these pairs were recorded as the first generation● Allele pairs were added or removed based on the rate of survival and reproduction to replicate the effects of

selective pressures.● The allele pairs were then counted and beads were added or removed depending on the rate of survival and

reproduction for each case.

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● Beads were picked out in pairs at random again; these signify individuals of the second generation.● This process was repeated for six generations for all runs except for one case due to a shortage of beads.

○ That run was carried out until the fourth generation; therefore, all comparative analysis can only be carried out to the fourth generation.

● The rates of survival and reproduction for our various runs are greatly exaggerated, with rates rare- if ever found in nature (cataclysmic events/uninhabited niches).

○ The exaggeration is so that we can see the explosive/depressive effects of adaptability or the lack thereof to a given environmental condition.

Results:● We found that if all the conditions for the Hardy-Weinberg Equilibrium were met, the allele and genotype

frequencies remained constant over several generations, as demonstrated in our base case.● However if the Hardy-Weinberg equilibrium was not met, then the frequencies of alleles changed over time, as

hypothesized.● The first case acts as our control case (see Figure 1).

○ This base case essentially demonstrates the fundamental principles of Hardy Weinberg; some of which include but not limited to random mating, the absence of natural selection and mutations, and all members of the population surviving and having equal reproduction rates.

● This graph (see Figure 4) entails the projections of the genotype frequency percentages up for prospective generations.

○ The pair of alleles with 0% survival (green) showed a decreasing trend line, those who remained neutral with no mutations (light blue and dark blue) display a constant projection (furthering propagating the Hardy Weinberg concept), and the pair of alleles with a positive survival rate (purple and orange) continued to increase logarithmically.

● In cases (see Rw, Figure 8) where a certain pair of alleles (ww) had a significantly low survival rate, it was possible to have a decreasing trend line for a heterozygous pairing showing a neutral mutation, despite the other allele having a neutral mutation. This is due to the low rate of random reproduction for Rw due to the limited overall availability for the w allele.● We found that although some homozygous genotypes had a downward trend towards extinction, the possibility of the genotype being reintroduced never reached zero due to the heterozygous genotypes.● In the negative 100% mutation towards the homozygous recessive genotype, the frequencies of red and white alleles were drastically altered. The white allele frequency declined and the red allele frequency increased, and both eventually stabilized because the homozygous recessive individuals disappeared within the population but the heterozygous individuals carried on the white alleles. There were not enough of heterozygous individuals for the homozygous recessive individuals to reappear, thus stabilizing the white allele frequency. (see graphs 3, 9, 12, 14, 18)● Heterozygous individuals carry a copy of the recessive allele in a population, harboring it against the normally negative homozygous gene. We would expect to see a consistently declining trend line but instead we see fluctuations due to heterozygous combinations. This enables homozygously negative alleles to maintain a presence in the gene pool despite poor survival rates.

Analysis / Discussion:● Allele combinations that are favorable represent a higher percentage in the population over several generations

while unfavorable combinations do the opposite and have less representation over time.● This selective pressure preferring advantageous phenotypes and weeding out adverse phenotypes results in a

phenomenon that we know as natural selection. This process repeated in a population over several generations is evolution.

● When mating is random in a large population with no disruptive factors, the law predicts that both genotype and allele frequencies will remain constant because they are in discussion.

● In this experiment, mutations acted as a disruptive force that affected the equilibrium because it introduced new alleles into the population and influenced the survival and reproductive rates.

● We can use the Hardy-Weinberg formula to find the allele frequencies and percentages of the individual alleles. This is an example for the control case.

○ p2 + 2pq + q2 = 1

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○ p2 = .24○ p = sqrt(.24)○ q2 = .26○ q = sqrt(.26)○ 2pq = 2[sqrt(.24)][sqrt(.26)] ~ .50○ 0.24 + 0.50 + 0.26 =1

● Our results are overall consistent with our hypothesis. The allele and genotype frequencies remained mostly constant when all the conditions for the Hardy-Weinberg Equilibrium were met; the mutations had the expected effects on the frequencies.

Conclusions / Further Considerations:● In this experiment we used beads of multiple colors to show that gene frequency remains constant over

generations in the absence of variation in other factors; we know that this rarely happens; generally there are fluctuations in the frequencies over generations.

● Simulation of the Hardy-Weinberg principle shows us the importance of factors such as natural selection and mutations.

● In order to further explore the principle of Hardy-Weinberg, we could design more cases with mutations and manipulate the rates of survival and reproduction for the alleles.

● We could introduce disruptions to the Hardy-Weinberg principle, such as immigration, emigration, non-random mating, and sex-linked genes in order to demonstrate the fluctuation of allele frequencies in nature, and further expand on the validity of the Hardy-Weinberg principle.

● This experiment has demonstrated the influence that various selective pressures have on the frequency of alleles in populations, and has shown us the importance of predation, mutation, gene flow, and other factors that act on flourishing populations.

● With the understanding that genetic variation plays an important role in evolution, we can expand our experiment to test, which outside influences have the most effect on the adapting population.

● We could test the concept of relative fitness by having a negative bias towards a certain allele that we deem less suited for a selected environment, so as to mimic predation.

ATTACHMENTS

Figure 1This is the control case for the experiment. There are no changes in allele frequencies, thus maintaining

the Hardy Weinberg principle.

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Figure 2This is the first case, in which the homozygous recessive alleles (ww) have a negative 33%, therefore there was only a 67% rate, and meanwhile the others had a 100% survival rate. The reason why Rw has a slight decrease is due to the fact that the available recessive alleles in the population were getting thrown out.

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Figure 3In this case, the homozygous recessive allele (ww) had a 0% survival rate. The other alleles (RR) and (Rw)

had 100% survival rates.

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Figure 4This figure represents and forecasts the overall allele frequencies when RR, Rw, and wB are neutral, while

RB and BB have survival rates of 150% and 200%, respectively. And finally ww had 0% survival.

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Figure 5This figure represents and forecasts the overall allele frequencies when RR, Rw, and wB are neutral, when

ww and BB have 0% survival, and when RB have a 50% survival rate.

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Figure 6This figure represents and forecasts the overall allele frequencies when there are varying survival rates for

each. RR has150% survival, Rw has 88% survival, ww has 300% survival, RB has 100% survival, wB has 50% survival, and BB has 10% survival.

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Figure 7This graph summarizes and forecasts only the homozygous dominant alleles (RR) throughout all of the

cases. Cases where it had a survival rate less than 100% resulted in a negative trend, whereas cases where it had a survival rate of more than 100% resulted in a positive trend. Cases in which the survival rate

was neutral or equal to 100% had trend lines that eventually resulted in constant frequencies over time. This not the case for RR since the availability of the R allele decreased over time.

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Figure 8This graph summarizes and forecasts the heterozygous alleles (Rw) throughout all of the cases. Cases

that contained survival rates of more than 100% resulted in a positive trend whereas cases that contained survival rates of less than 100% had a negative trend. Cases in which the survival rate was 100% or neutral

should result in constant frequencies. In this graph, the general rules above for the cases were not all applicable since the availability of the w allele was reduced over time.

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Figure 9This figure represents the homozygous recessive (ww) alleles throughout all of the cases. The trend lines

showed a decrease in trend when the mutation resulted in less than 100% survival and showed an increase in trend when the mutation was above 100%.

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Figure 10This figure shows the phenotype frequency of alleles for the base case, specifically that red alleles are

more frequent than those of white.

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Figure 11This figure shows the phenotype frequency of the traits for the mixed mutation case. The phenotype with ww had an increasing trend since it had a survival rate of 300%, whereas the other traits had decreasing

trends as a result of the limited availability of the black and red phenotypic frequencies.

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Figure 12This figure shows the phenotypic frequency for the negative mutation case. Whereas the red individuals

(RR, and Rw were neutral) had a frequency decline, white (ww at a 0% survival) had an increase and decrease, and finally the black (wB, 50% survival and BB, 0% survival) decrease and increase.

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Figure 13This figure shows the phenotype frequency for the positive mutation case. The alleles for black (BB) had a

positive trend since it has a 200% survival rate. The other pair of alleles for red and white showed a decrease in trend line due to 2 reasons: the white alleles had a 0% survival and there is a limited

availability of the R allele.

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Figure 14This figure shows the phenotypic frequency of the 0% survival of homozygous recessive (ww) alleles. This illustrates the abundance in the red phenotypic trait since there is an ample amount of R alleles with 100%

survival in this case.

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Figure 15This figure shows the phenotypic frequency of the 0% survival of homozygous recessive (ww) alleles. This illustrates the abundance in the red phenotypic trait since there is an ample amount of R alleles with 100% survival in this case. This is similar to Figure 15, but differs in such a way that the phenotypic frequency of

whites is slightly higher for this case since the survival rate is increased.

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Figure 16This figure represents the percentage of allele frequencies in the base case; since the allele frequencies had no fluctuations and resulted in frequencies that were almost all similar, the phenotypic percentages

showed an almost constant trend line with no significant variation in numbers.

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Figure 17This figure shows the allele frequency for the -33% survival for the ww individuals. The frequency of the

red allele increased over time, due to its dominance and 100% survival rate. The white allele, ww, at a survival of 67% decreased steadily.

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Figure 18This figure shows the allele frequency for the -100% survival for the ww individuals. The frequency of the

red allele increased over time, due to its dominance and 100% survival rate. The white allele, ww, at a survival of 0% decreased and leveled out.

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Figure 19This graph summarizes the allele frequency percentage for the positive mutation case. The white

phenotype shows a dramatic decrease in representation since it has a 0% survival, whereas the red and black phenotypes continued to have a positive trend line since their alleles had either neutral, 100%, or

greater than 100% survival rates.

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Figure 20This figure shows the allele frequency for negative mutation case, where homozygous dominant, and heterozygous (Rw) were neutral, and RB, had a 50% survival rate, therefore causing the red allele to

decrease. Which ww, still having an availability of alleles had a positive increase in frequency. And finally the black allele, with 0% survival had a decrease.

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Figure 21This figure shows the allele frequency percentages for the mixed mutation cases. The white phenotype

shows an increase due to the 300% survival rate of the homozygous recessive allele pair; this creates an abundance of w alleles in the pool. The red and black trend lines show variations since their survival rates

for the allele pairs fluctuate.

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Info Images

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Image 1Random mating for the second case

Image 2Random mating for the third case

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Image 3Random mating for the fourth case

Image 4Random mating for the fifth case

References / Literature Cited: Medical Practice uses APA Standards for Citations.1. Reece, J. (2011). Campbell biology Jane B. Reece ... [et al.]. (9th ed.). Boston: Benjamin

Cummings.

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2. Robinson, Richard. Hardy-Weinberg Equilibrium. Genetics [Internet]. 2003 [cited 2015 Feb 26]; 2: 133-136. Available from:

http://go.galegroup.com.ezproxy.solano.edu/ps/i.do?id=GALE%7CCX3406500134&v=2.1&u=fair48947&it=r&p=GVRL&sw=w&asid=bacf44196499b0c3212fbf829514e6b2

3. Alan R. Lemmon. Evolutionary Genetics: H-W Equilibrium [Internet]. [cited 2015 Feb 26]. Available from: http://www.evotutor.org/EvoGen/EG1A.html.

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