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Considering again the guppy populations with and without crayfish, researchers have sampled genotypes over several generations, with the clear expectation that the R allele should quickly fix in the population with crayfish due to selection. However, this was not observed, and the B allele was routinely found in the downstream population for as long as observations were made. What is the most likely population genetic process preventing the complete fixation of the R allele in the downstream population?

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Jean Keeling
Jean KeelingLv2
28 Sep 2019
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Related questions

Q1. What are alleles?Different forms of the same gene.Different genes.The different characteristics of an organism.Genes found only in humans.Q2. If you add up the frequency of homozygotes + the frequency of heterozygotes for one gene (i.e. at one locus) in a population, what number do you get?Q3. People who are heterozygous for the sickle-cell allele:Are susceptible to malaria but not sickle-cell anemia.Are susceptible to sickle-cell anemia but not malaria.Are not susceptible to either sickle-cell anemia or malaria.Are susceptible to both sickle-cecell anemia and malaria.Q4. In the case study in this lab, which genotype is represented by "2pq" in the Hardy-Weinberg equation?Homozygous HbAHomozygous HbSHeterozygous HbA/HbSNo specific genotypeQ5. Suppose that, in an isolated village, the proportion of individuals that have sickle-cell anemia is 0.1 (or 1 of every 10 people). What proportion of the population should be sickle-cell carriers, according to Hardy-Weinberg expectations?Q6. When you simulated the elimination of malaria at the beginning of the lab, once the allele frequencies stabilized, what was the frequency of the HbA allele?Q7. When you investigated regional differences, what was the frequency (over many generations) of the HbS allele in the village in the "slightly wet" part of Africa?Q8. What is the number of deaths due to sickle-cell anemia in a region without mosquitoes expected to be?Very lowVery highModerateRelated to the frequency of malaria allelesQ9. As long as there are multiple alleles of a gene in a population, why will the frequencies of the alleles always change over time?Because natural selection changes all allele frequencies in populations over time.Because genetic drift causes random fluctuations of allele frequencies in populations.Because diseases will eliminate some of the alleles, generating fluctuations in their frequencies.Because allele frequencies fluctuate before the alleles eventually become fixed.Q10. Imagine a huge population with a gene that has ten functionally equivalent, neutral alleles. A small but genetically representative group of individuals from the big population is transported to an island, forming a small population. Which of the statements below best describes what will likely happen over time, and why?Because natural selection doesn't act on neutral alleles, the frequencies in the two populations should remain the same over time.Genetic drift will cause one allele to first become fixed in the island population, and later to become fixed in the original, large population.Genetic drift will result in the allele frequencies of the two populations diverging over time, with alleles being lost sooner in the island population.The allele frequencies of the two populations will change similarly due to a combination of genetic drift natural selection.

In a small paragraph, compare and summarize these two articles.

Article 1 Description

This article is an observational study, which discusses how frequency dependent selection affects two phenotypes of a predator through differential guarding response. The researcher examines the ratio of handedness of two samples of P. microlepis collected from two adjacent sites along Lake Tanganyika’s northwestern shoreline for a period of eleven years. The process of observations includes observing the correspondence between the handedness of P. microlepis and their targeted prey (Hori, 1993). The researcher carried observations to identify the direction from which P. microlepis attacked the flank of their prey. Moreover, the researcher used a gill net to catch each P. microlepis that attacked the lure. Catching the P. microbes made it possible for the researcher to observe its features and determine its handedness. The researcher determined the handedness of the scales of P. microlepis by observing the fish under a microscope.

During the period of study, Hori (1993) established that the ratio of handedness of P. microbes remained at 0.5 for each one-to-two year intervals throughout the eleven years of the study. Further investigations on temporal changes in handedness ratio showed that the ratio oscillated with amplitude of 0.15 within a five-year period (Hori, 1993). These observations were made for the two species of P. microlepis under investigation. The researcher concludes that the direction of mouth opening of scale eating cichlid fish in Lake Tanganyika is determined by the genetics of the fish. The researcher demonstrates that frequency-dependent natural selection determines the number of left-handedness or right-handedness fish. Based on researcher’s observations, when right-handed fish attack from behind, they snatch the scales from their prey from the left flank (Hori, 1993). On the other hand, when left-handed fish attack their prey from behind, they attack the right flank (Hori, 1993). Therefore, fish with rare phenotypes are more successful as predators than ones that have the more predominant phenotype. This study can be used to guide researchers who are interested in seeking ways of increasing the population of different species of fish. It can also be used as a basis for investigations on how fish type determines its survival tactics or predator tactics.

Article 2 Description

The study was an experimental analysis which sought to quantify phosphoglucose isomerase (Pgi) frequency change over a period of time and compare Pgi genotypes based on physiological responses to high temperatures and subzero thermal extremes encountered by beetles in nature. The research seeks to establish how the local climate in Bishop relates to changes in allele frequency at Pgi and other allozyme loci. It also seeks to establish if ambient temperature of beetle habitants rise to levels that expose beetles to stressful temperature. The researcher also seeks to establish how Pgi genotypes differ physiologically when exposed to subzero temperatures. By answering these questions, the researcher will establish the relationship between changes in enzyme genotype frequency and regional climate changes in addition to investigating major physiological mechanisms through which animals respond to change in climate.

To answer research questions and test research hypothesis, the researchers carried out several experiments and analyses of data. The experimental study involved collecting adult beetles that had emergent recently from pupae for a period of one year between August 1988 and August 1989 (Rank & Dahlhoff, 2002). Their genotype was determined at five different polymorphic enzyme loci. Some of the things analyzed during the study include fluctuations in climate and allele frequency change; daily and annual mean values of air temperature, Effects of Pgi genotype on HSP70 expression, and quantification of Pgi genotype on HSP70 expression among other things (Rank & Dahlhoff, 2002). The study results revealed that although beetle populations were genetically different the FST-values for 1996 were greater for each enzyme locus than those for 1998 (Rank & Dahlhoff, 2002). Moreover, researchers established that the frequency of Pgi allele had increased by 11 percent, a trend that was not observed for all the other loci investigated. Therefore, the researchers conclude that Pgi genotype differences in thermal physiology account for Pgi allele frequency change in nature. Contrary to selected hypothesis that the frequency of Pgi allele should increase with decrease in temperature, the study established that the frequency of Pgi allele decrease with decrease in temperature. This work is important because it provides a basis for more research on how variations in temperature affect beetle populations. The study findings can be used to guide researchers who are interested in seeking ways of protecting endangered beetle populations in different climatic conditions.

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