Drosophila melanogaster. Introduction. Drosophila melanogaster is a kind of flies fruit fly that is widely used in genetic

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1 Jessie Tran Mrs. Lajoie Honors Biology Date of Experiment: 4 May 2015 Due Date: 12 May 2015 Determining the Inheritance Patterns of Purple Eyes, Lobe Eyes, and Yellow Body Genes of Drosophila melanogaster Introduction Drosophila melanogaster is a kind of flies fruit fly that is widely used in genetic experiments to understand the biology of genes, or specifically inherited genetic patterns (1). In this experiment, three traits of Drosophila melanogaster purple eyes, lobe eyes, and yellow body will be observed to find their inheritance patterns, whether if they are dominant, recessive or X-linked recessive. Due to the wide use of this species of flies, it is important to know more about this species and its traits to have further understanding for any future use. The understanding of this experiment also contributes to the knowledge of inheritance patterns, which is very essential in terms of studying human s inheritance patterns (2). This understanding will help to prevent or predict the diseases or disorders of a human based on their families and their genes and lower the risk and dangerous situation that could happen (3). In this experiment, Chi-Square Analysis would be used. If the level of signifance, p>0.05, then there is no significant difference between what was predicted and observed, so the results support the predicted inheritance patterns. Gregor Mendel s principles of inheritance will be used to hypothesize the percentage of flies we will obtain for the dominant and recessive trait. Based on his experiments, Mendel

2 proposed when a homozygous dominant and homozygous recessive alleles breed, the F 1 generation will only consist of heterozygous genotypes, which the dominant traits will be expressed in all of the offspring of this generation (Figure 1). However, when letting two individuals with heterozygous genotypes (from the F 1 generation) breed with each other, the F 2 generation will consists of approximately 25% homozygous dominant genotypes, 50% heterozygous genotypes, and 25% homozygous recessive genotypes. This also means that 75 percent of the F 2 generation will have and express the dominant trait, and only 25 percent will have the recessive trait (Figure 2). A A A Aa Aa a Aa Aa Figure 1: The Punnett Square indicates the inheritance patterns in F 1 generation of the breed between a homozygous dominant and a homozygous recessive allele. The capitalized A represents the dominant allele, and the lowercase c represents the recessive allele. A a A AA Aa a Aa aa Figure 2: The Punnett Square indicates the inheritance patterns of F 2 generation between two heterozygous individuals from F 1 generation. Therefore, in terms of dominant and recessive traits, it is hypothesized when a homozygous dominant genotype mate with a homozygous recessive genotype, the F 1 generation will all express the dominant trait, and the F 2 generation will have about 75% individuals carry dominant trait and 25% individuals carry recessive trait.

3 Based on Gregor Mendel s principles, Thomas Morgan developed the rules of inheritance patterns in terms of sex-linked traits (4). When a female has the X-linked recessive trait, which both of its X chromosomes are affected by the trait, is allowed to mate with a normal male, all of the F 1 female offspring are carriers and all of the male offspring are affected by the recessive trait (Figure 3). When a female carrier and an affected male from F 1 generation are allowed to mate to create the F 2 generation, approximately 50% of the female offspring are affected and the other 50% are only carriers; about 50% of the male offspring are affected and the other 50% are normal (Figure 4). X b X b X X b X X b X Y X b Y X b Y Figure 3: The Punnett Square indicates the inheritance patterns in F 1 generation of the breed between an affected female and a normal male. The capitalized X represents the X chromosome, the capitalized Y represents the Y chromosome, and X b represents the X chromosome that carry the gene of the trait. X b X X b X b X b X b X X X b Y XY Figure 4: The Punnett Square indicates the inheritance patterns of F 2 generation between a female carrier and an affected male, both from the F 1 generation. Thus, in terms of the sex-linked trait, it is hypothesized when mating a normal female with an affected male will get all females that do not express the trait, who are only carriers, and

4 all affected male in F 1 generation; the F 2 generation will consists of about 25% of each type: affected females, carrier females, affected males, and normal males. Results The first trait tested was purple eyes. In the cross between wild type and purple eyes, the F1 generation was composed of only wild type flies, heterozygous genotypes. In the cross among the F1 generation to produce F2 generation, the F2 generation was composed of 899 wild type flies and 305 purple eyes flies, χ 2 (1,1204)=0.07, p=0.79 (Figure 5). In terms of observed percentage, wild type flies is 74.67% and purple eyes flies is 25.33%. Results of the F 2 Generation when Breeding Wild Types with Purple Eyes Expected Expected Observed Number Observed Percentage if Percentage if (Individuals) Percentage (%) Recessive (%) Dominant (%) Wild Types Purple Eyes Total Figure 5: The observed percentage is about the same with the expected percentage if the trait is recessive (the difference is about 0.33%). The second trait tested was lobe eyes. In the cross between wild type and lobe eyes, the F1 generation was composed of only lobe eyes type, heterozygous genotypes. In the cross among the F1 generation to produce F2 generation, the F2 generation was composed of 209 wild type flies and 909 lobe eyes flies, χ 2 (1,1199)=0.44, p=0.50 (Figure 6). In terms of observed percentage, wild type flies is 24.19% and lobe eyes flies is 75.81%.

5 Results of F 2 Generation when Breeding Wild Type with Lobe Eyes Expected Expected Observed Number Observed Percentage if Percentage if (Individuals) Percentage (%) Recessive (%) Dominant (%) Wild Types Lobe Eyes Total Figure 5: The observed percentage is about the same with the expected percentage if the trait is dominant (the difference is about 0.81%). The last trait tested was yellow body. In the cross between wild type and yellow body, the F1 generation was composed of all wild type female, carriers, and all yellow-body males. In the cross among the F1 generation to produce F2 generation, the F2 generation was composed of 297 female with yellow bodies, 305 male with yellow bodies, 300 wild type females, and 319 wild type males, χ 2 (3,1221)=0.93, p=0.82 (Figure 7). In terms of observed percentage, female with yellow bodies is 24.32%, male with yellow bodies is 24.98%, female wild type is 24.57%, and male wild type is 26.13%. Results of F 2 Generation when Breeding Wild Type Males with Yellow Body Females Observed Number (Individuals) Observed Percentage (%) Expected Percentage of X-linked recessive (%) Yellow Body (Female) Yellow Body (Male) Wild Type (Female) Wild Type (Male) Total

6 Figure 7: The observed percentage is about the same with the expected percentage if the trait is X-linked recessive (the difference is from 0.03% to 1.13%). Discussion According to the hypothesis, when a homozygous dominant genotype crosses with a homozygous recessive genotype, the F 1 generation will have all heterozygous genotypes and the dominant trait will be expresses, F 2 generation (after letting the cross among F 1 generation happen) will consist of 25% homozygous dominant, 50% heterozygous, and 25% homozygous recessive, which 75% will express the dominant trait and 25% will express the recessive trait. In the first crossing with purple eyes, the trait shows that its results of the F 2 generation are nearly the same with how the F 2 generation results of a recessive trait should be. The observed percentage of the purple eyes is (305/1204) x 100%= 25.33% of the total F 2 generation offspring, which is approximate the expected percentage of a recessive trait (25%) given in the hypothesis. The level of significance p is 0.79, larger than 0.05, suggests that there is no significant difference between the observation and prediction, so the results support the predicted inheritance pattern. Thus, purple eye is a recessive trait of Drosophila melanogaster when crossing with wild type. Lobe eye is the second trait to be crossed to find the inheritance pattern. Based on the experiment, the result of this trait in F 2 generation is (909/1199) x 100%= 75.81%, approximately the same with how the F 2 generation results of a dominant trait should be, 75%. The level of significance p is 0.50, larger than 0.05, suggests that there is no significant difference between what is observed and predicted, so the results support the predicted

7 inheritance pattern. Therefore, lobe eye is a dominant trait of Drosophila melanogaster when crossing with wild type. An X-linked recessive trait is different from the normal dominant or recessive trait. The gene of the trait is coded on the sex chromosome, but only on X chromosome, not Y chromosome. Female is composed of two X chromosomes, and male is composed of one X chromosome and one Y chromosome. Because female has two X chromosomes, only when both of her chromosomes are affected by the trait, the trait expresses; if only one is affected, that female is only a carrier. Male is different from female by having only one X chromosome. Thus, when that X chromosome of the male is affected, the trait expresses. The trait is recessive because if only one X chromosome in the two X chromosomes of female is affected, then the female is only a carrier. When crossing an affected female with a normal male, the F 1 generation only consist of female carriers and affected males, the F 2 generation will consist of 25% of each type: affected females, affected males, female carriers, and normal male (the cross in figure 3 and 4). The yellow body gene after crossing also shows the same pattern, each type also consists about 25% of the total. Thus, yellow body trait is an X-linked recessive trait of Drosophila melanogaster. Based on the analysis of the traits after crossing with the normal wild type, the following conclusions were made: the purple eyes trait is recessive, the lobe eyes trait is dominant, and the yellow body trait is X-linked recessive.

8 References (1) "The Fruit Fly and Genetics." The Wonderful Fruit Fly. UNC Baccalaureate Education in Science and Teaching. Web. 11 May < (2) Alliance, Genetic. "Understanding Genetics: A New York, Mid-Atlantic Guide for Patients and Health Professionals." INHERITANCE PATTERNS. U.S. National Library of Medicine, Web. 11 May < (3) Alliance, Genetic. "Understanding Genetics: A New York, Mid-Atlantic Guide for Patients and Health Professionals." INHERITANCE PATTERNS. U.S. National Library of Medicine, Web. 11 May < (4) Alliance, Genetic. "Understanding Genetics: A New York, Mid-Atlantic Guide for Patients and Health Professionals." INHERITANCE PATTERNS. U.S. National Library of Medicine, Web. 11 May <