Effects of Eye Pigmentation in Drosophila melanogaster
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This study explores the eye pigmentation process in Drosophila melanogaster through reciprocal crosses of cinnabar and white-eyed flies. The results show unexpected phenotypes in the F1 and F2 generations, indicating the influence of genetic and environmental factors.
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The Effects of Eye Pigmentation inDrosophila melanogasterwith Consideration of Reciprocal Crosses Biology-Genetics
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Abstract Eye pigmentation process is an essential aspect in assessing mutation process. Drosophila melanogasterhas been used as an effective organism in the assessment of this pigmentation over the years. Testing ofcinnabarfemale crossed bywhitemales and an eventual reciprocal process was undertaken. This process entails a critical understanding of how pigmentations are often crossed to assess pigmentation. TheDrosophila melanogaster produces eye pigmentation whilecinnabarallele associated with the protein. This practical assessed crossing of two genes using the parents’ genotype in order to obtain the F1 and later F2 generations. Phenotypes produced were the key focus of this study. The hypothesis of the study entailed an assessment of crossing thewhitefemales with thecinnabarmales to get the F1 generation. Further F 2 generations were undertaken with predictions of obtaining wild type color andcinnabarmales. The results obtained indicated that crossing four cinnabar males and two white femalesresulted, furtherCinnabar males were crossed with white females, yieldingwild type females and white males. In the F2 generation, there are far fewer white apricots and far more double mutants than expected. (X2=249, d.f.=3, p<0.0001). Reciprocal process plays a vital role in the overall mutation process. Environmental factors are critical in gene mutation which could have a significant impact on the occurrence of dominant and recessive genes as observed in the results. Adjustment son the overall mutation on the environment is key towards achieving maximum mutation.
Introduction In this experiment, we tested the eye pigmentations ofcinnabarwithwhiteeyes on Drosophila melanogaster. We usedD. melanogasterbecause it is a good model organism due to its short life span and large number of offspring. We tested the eye pigments with a cinnabarfemale crossed bywhitemales and did the reciprocal of that. The experiment was conducted to understandeye pigmentations and how they are transported. ForD. melanogaster,it produceseye pigmentation through pigment pathways, which thecinnabar allele is a pigment protein which is involved in the actual pigment production, while thewhite allele is a transport pigment which transports the pigments into the eye. The brown pigmentation is given off by chromosomes which is synthesized in the pigment pathway and gives off the color. There is also the pigment ptendines which gives off the color red and yellows. While the white pigmentation is due to a lack of pigment in the eyes and the white is also a transporter which does not produce enzymes, but transports the pigments to the eyes. Thecinnabargene is located on the 2R chromosome while thewhiteis located on the X-chromosome. The eye pigmentation ofcinnabaris not autonomous in development (Beadle and Ephrussi 1936) while thewhitegene is x-linked. For the mutant cells of cinnabar, the cells with the mutant genotype will not have a mutant phenotype if they are in an organism or population of cells that have the wild-type genotype.(Beadle and Ephrussi 1936) We performed our experiment by crossing the parents (p-generation) to get the F1 generation and then crossed the F1 generations to get F2 generation. The F2 generations were then scored to understand the pigmentations more in depth by looking at the phenotypes produced and to understand the results when these two eye pigments were crossed. Our hypothesis when crossing bothcinnabarmalesandwhite apricotfemales, we predicted that our F2 generation females would be wild-type eye color, and our males would
becinnabar.Due to thewhite apricotgene being on the X-chromosome, we also predicted that the F2 generation would consist of double mutants (orange).When crossing thewhite females with thecinnabarmales we predicted that all the F1 generation would be wild-type eye color. Materials and Methods Two strains ofDrosophila melanogasterwere used in the study, flies with either cinnabar or white eyes. Both phenotypes for the parental generation were obtained from stock maintained at UW-Whitewater. The genotypes for the two parents were as follows: 1. cinnabar females (cn/ cn, Xw+/Xw+) and white males (cn+/cn+, Xw/Y) 2. cinnabar males (cn/cn, Xw+/Y) and white females (cn+/cn+, Xw/Xw) Both the species were reared on a diet that comprised of molasses medium and standard cornmeal. The medium had supplementary live yeast grains, with the aim of promoting egg laying. The two parental species were maintained in 25-30ml vials that were closed with foam plugs and stored in an incubator maintained at 25 degrees Celsius. Two crosses were performed for the experiment. The first one involved crossing four cinnabar males and two white-eyed females. The second one involved a reciprocal cross between parental phenotypes of four cinnabar females and two white-eyed males. All females used in the parental crosses were confirmed to be virgins, so there would not be a change of a female sorting sperm for another male from a different mating. One week after establishing the parental crosses, all vials were checked for larvae and the adults were removed and discarded in a flask containing 70% EtOH. For one pair in group three, cinnabar females were crossed with white males. This cross failed to produce larvae, even when the crosses were attempted a second time. The second pair was white females crossed with cinnabar males. This cross did produce larvae, so
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the adults were removed and anesthetized, confirmed for the phenotype and gender, then discarded in the flask with 70% EtOH. These vials were incubated for another week, then the F1 adults were anesthetized and sorted by gender and phenotype under a dissecting microscope. The F1 results were supposed to produce wild type females and white males by crossing the cinnabar males and white females. Dr. Kriska allowed Group three to use the F1 wild type females and some white apricot males because there were no available white males. After one week establishing the F1 crosses, the bottles were checked for larvae, the adults were removed and anesthetized, and their numbers and phenotypes confirmed using a dissecting scope before being disposed of in the flask with 70% EtOH. The following week, adult F2’s was anesthetized and sorted by gender and phenotype. There was no F2 generation for the cross between all wild-type flies that were obtained after mating between four cinnabar males and two white females. On the other hand, the cross conducted between eight cinnabar males and eight white apricot females of F1generation resulted in four dissimilar phenotypes in the F2generation namely, (i) white apricot, (ii) wild-type, (iii) cinnabar, and (iv) orange (double mutant). Prominence of the differences between all the flies obtained in the F2generation were determined by using a chi squared test compare the observed and expected numbers of flies in our four observed categories: wild type, white apricot, cinnabar, and double mutants, which had a light orange color. Results (F1 Results of Original Parental Crosses) WhenD. melanogasterwas crossed with four cinnabar males and two white females, the F1 offspring of the F1 generation were seven wild type. However, when three cinnabar females were crossed with three white apricot males, the F1 generation offspring produced
five wild-type females (red) and three cinnabar males. Cinnabar males were crossed with white females. This cross would result in wild type females and white males. Cinnabar females were crossed with white apricot males. This cross would result in wild-type females and males. (F2 results from F1 Crosses) The expected ratios of offspring were 3/8 wild type, 3/8 white apricot, 1/8 cinnabar, 1/8 double mutant. After observing these four categories, the double mutants showed and orange phenotype. The F2 results are shown below in Table 1. Phenotype# observed (both sexes) # expected (observed - expected) ^2 / expected White apricot Males=8 Females=36 44193.5115.5 Wildtype Males=98 Females=129 227193.55.8 Orange (Double Mutant) Males=78 Females=72 15064.5113.3 Cinnabar Males=40 Females=55 9564.514.4 Total/Sum516516249 Table 1.Table 1 shows the observed and expected numbers of wild type, white cinnabar, and orange double mutant F2 phenotypes. There are far fewer white apricots and far more double mutants than expected. (X2=249, d.f.=3, p<0.0001). Discussion
The results obtained from this assessment illustrate that the crossing of the P generation led to wild type phenotype of both females and males. This was quite contrary to the expectations of this study being sought. The hypothesis tested attempted to assess the cross on the parents between thecinnabesand white females. In all variation conducted, there was the presence of wild type F1 generation offspring. The wild type flies – red eyes carrier the white allele and white-eyed flies carry the white allele. The development of the brown pigment obtained from the pigment pathways is responsible for the color development of the F1 generation wild type. Despite this fact, some of the F1 generations generated other different offspring of cinnabar males. Crossing the cinnabar males which its location is situated on the 2 R chromosome and the autonomous, occurrence of would type and white males were obtained due to the effect the white gene is located on the X chromosome thus being homozygous to the offspring (Hardon & Mitchell 1951). More often F1 have unique mutation obtained from mutation of inheritance from parents’ gremlin. The F1 stage results in dominant mutations obtained from the parent's gene. The presence of mutant cells gene situated on the cinnabar do not allow for the production of mutant phenotypes hence giving off different colors of wild type males and white makes. This pathway depicted shows different mutations; similar phenotypes often occur as a result of different mutations. In the second assessment, the study tested various crosses ofcinnabarmalesand white apricotfemales, with of production of wild type eye color females and males being the cinnabar.Further, due to X –chromosome on the apricot gene, F2 prediction was expected to consist of double mutants’ genes having an orange color. The results yielded far more than the expected results. White apricot having X chromosome having 8 males and 36 females were obtained against the expected value of 193.5, while the wild type and organ double mutant were overexpressed at p-value 0.001 as observed in table 1, the expected output was widely affected by various factors during the production process. Factors often affect
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reproduction rate and thus affecting the growth development. Eggs hatched during the cross over did not attain the needed stable conditions for the development and reproduction to occur effectively in the mutations process (Kamleh et al., 2009). The double mutants were far much more than expected while the white apricots were far much less. This could be attributed to too few males in the white apricot affecting its production levels and fewer males in thecinnabaralso this lead to more females being produced (Mertenes & Hammersmith, 2007). The chi-square obtained indicating the difference occurring between the different mutations and phenotypes offsprings of F2 generation are occurring by chance. Thus the effect of the reciprocal process in mutation could have a role to play. The effect of the reciprocal process undertaken in this task could have an impact on the overall gene variation of the F2 phenotypes. The role of the parental sex gene on the overall F2 phenotype could have been influenced through the subjection of environmental factors limiting its expression. Female offspring g carrying the mutant white eye allele but do not offer phenotypically thus indicating recessive gene (Kim, Kim & Yim, 2013). Assessing parental mutation allows for crossing for the desired trait. The phenotypes occurrence was attributed to overexpression and underexpression of the parental genotypes genes leading to alteration in the crossing process. Further environmental changes could have an effect on the overall progeny mutation process (Reame, Knecht & Chovnk, 1991). In the reciprocal process, the male offspring which are white eyed often tend to give red-eyed female offspring. The presence of recessive genes has led to the development of cinnabar and orange double mutants which have been overexpressed while recessive genes are associated with lower expressions of white apricot and wild type females and males respectively (Ziegler, 2003).
Thus the results obtained in this study during thecrossing thewhitefemales with the cinnabarmales prediction on F1 generation did not offer purely wild types mutations. Further, the F2 generation results yielded fewer white apricots and more double mutants than expected. Thus the ire is needed to improve on the overall reciprocal process and subsection of temperature as it signifies alterations on the gene mutations in cross over effects of phenotypes.
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