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BIOL 2301

Analysis of the Inheritance of Eye color and Wing Pattern in Drosophila Melanogaster Molecular Genetics Lab, Tues 2:50 Melissa Johnson Maggie McCrann 11-06-07 Johnson 2 The fruit fly, Drosophila Melanogaster, is a model organism perfect for use in the study of biologically inherited traits. Fruit flies possess many traits that make it easier to study than other, more complex organisms. They have a short life cycle, shortening the duration of a single experiment. Size and ease of care are also taken into account when choosing a model organism. Fruit flies require very little space to survive and are very easily cared for, making them an ideal model organism for experiments carried out in the laboratory (Begley, 4). In this laboratory exercise, Drosophila Melanogaster will be used to study the inheritance pattern of eye color and wing development from one generation to the next. Analysis of a series of fruit fly crosses will provide enough data to evaluate the mode of inheritance for eye color and wing development (Begley, 4). This will give a comprehensive look into the discoveries made by Gregor Mendel and Thomas Hunt Morgan in the field of genetics. The work of Gregor Medel plays a central role to the study of genetics. His research led to the discovery of several laws governing the inheritance of traits. Mendel’s first law, the Law of Segregation states that offspring inherit one version of a gene from the father and one version from the mother (Hartl, 42-47). These versions of genes are called alleles and separate independently in gametes. It also states that in the offspring, the dominant allele will be Johnson 3 expressed and the recessive allele will not be expressed (Hartl, 42-47). Mendel’ second law, the Law of Independent Assortment, states that alleles for different traits segregate independently of one another (Hartl, 47). Thomas Hunt Morgan was a geneticist whose work led to the discovery that genes are contained on chromosomes, making it possible for certain genes to be sex-linked or carried down on the X chromosome (Hartl 100). This was proven by Thomas Hunt Morgan through the study of the inheritance of eye color in fruit flies. The mutation that leads to white eyes in Drosophila Melanogaster is the result of a metabolic block that knocks out both the scarlet pigment and brown pigment (Hartl 100-101). The effects of this metabolic block can be seen throughout this experiment in the white-eyed progeny. The works of both Gregor Mendel and Thomas Hunt Morgan play a central role in the study of genetics. In this multi-week experiment their discoveries and processes leading to these discoveries can be observed first-hand. The chromosome theory of heredity and laws of Mendelian genetics can be witnessed and studied in order to better understand the research behind modern-day genetics. Materials and Methods The laboratory manual for Genetics and Molecular Biology was followed during this multi-week experiment. Three clean culture vials were set up the first week with instant medium and 1 grain of dry yeast. Vestigial-winged, red-eyed males, and a normal winged, white-eyed virgin female were added to these vials to create the first, Parental (P1) cross. The second week, the cultures were checked, and the parents transferred to the morgue to avoid mixing the P 1eneration with their offspring. Carbon dioxide was used in this experiment to anesthetize Johnson 4 the flies in order to move them to the morgue. The third week, the total number of flies in each vial was recorded as well as phenotype and gender combinations. Three new vials were set up for the 1 cross with white-eyed, normal-winged males and wildtype females. The fourth week was another week of culture maintenance. Parents were again transferred to the morgue to preserve the accuracy of the data. The final week, the2F generation was analyzed for eye color and wing combinations. The total number of flies was recorded as well as gender and phenotypes. A chromatographic analysis of eye pigment was also carried out for 2 flies of each phenotype (Begley 4-10). The only deviation made from the lab manual procedure was the exclusion of one vial from the P1cross which contained vestigial flies. None of the offspring from the parental cross should have had vestigial wings. The only explanation of this is if a vestigial winged fly was mistakenly put into the vial by accident which would have caused some of the offspring to express vestigial wings. Results Key Vg- Normal Wings vg- Vestigial Wings W- Red Eyes w- White eyes Table 1 W w w vgvgX Y x VgVgX X P1Cross vgY vgX W w w W w VgX VgvgX Y VgvgX X VgX w VgvgX Yw VgvgX X w 50% White-eyed, Normal wing males 50% Red-eyed, Normal wing females Johnson 5 The Parental cross was made between vestigial wing, red-eyed males and normal wing, white-eyed females. This cross can result in only two types of offspring, white-eyed, normal wing males and red-eyed, normal wing females. A fly with vestigial wings was mistakenly placed in one of these vials. This resulted in skewed data which was disregarded in the final count of flies and phenotypes. Table 2 w W w VgvgX Y x VgvgX X w w F1CrWss vgY W vgX W w VgY W VgX W w vgX vgvgX Y vgvgX X VgvgX Y VgvgX X vgX w vgvgX Y vgvgX X w VgvgX Yw VgvgX X w W W W w W W w VgX VgvgX Y VgvgX X VgVgX Y VgVgX X VgX w VgvgX Y VgvgX X w VgVgX Yw VgVgX Xw w Ratios 1:1- male:female 1:16 – Vestigial wing, red-eyed male 1:16 – Vestigial wing, red-eyed female 1:16 – Vestigial wing, white-eyed male 1:16 – Vestigial wing, white-eyed female 3:16 – Normal wing, red-eyed male 3:16 – Normal wing, red-eyed female 3:16 – Normal wing, white-eyed male 3:16 – Normal wing, white-eyed female Table 3 Experimental Results Female Male Wildtype 73 63 White 80 69 Vestigial 31 35 Vestigial/White 36 31 Total 220 198 The actual results obtained from t1e F cross are shown above. The cross resulted in 198 male flies and 220 female flies. Out of the male progeny: 35 were vestigial with red eyes; 31 were vestigial with white eyes; 63 were normal winged with red eyes; and 69 were normal winged with white eyes. Out of the female progeny: 31 were vestigial with red eyes; 36 were Johnson 6 vestigial with red eyes; 73 were normal winged with red eyes; and 80 were normal winged with white eyes. Table 4 Chi Squared Results- Experimental Data Phenotypes Observed Expected (O-E) X = ∑ (O-E) /E W vgvgX Y 35 26 9 3.12 vgvgX X w 31 26 5 .96 vgvgX Y 31 26 5 .96 w w vgvgX W 36 26 10 3.85 VgvgX Y 63 78 -15 2.88 VgvgX X w 73 78 -5 .32 VgvgX Y 69 78 -9 1.04 w w VgvgX X 80 78 2 .05 Total 418 416 13.18 Table 5 Sample Results Female Male Wildtype 187 191 White 182 177 Vestigial 69 71 Vestigial/White 62 61 Total 500 500 Table 6 Chi Squared Results- Sample Data Phenotypes Observed Expected (O-E) (O-E) /E vgvgX Y 71 62 9 1.31 W w vgvgX w 69 62 7 .79 vgvgX Y 61 62 -1
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