Abstract
Drosophila melanogaster was the organism used trough the experiment to look at hour a monohybrid, dihybrid and sex-linked traits work. For monohybrid, brown body was crossed with ebony body to look at the segregation of genes, which will give the F1 generation all brow bodies, F2 generation ratio of 3:1. In dihyrid, sepia eyes were crossed with vestigial wings to look at how the alleles separately independently, giving F1 generation all normal eyes and mutant wings but F2 generation the phenotypic ratio of 9:3:3:1. And finally the sex-linked cross was made betweek white eyes female and red eyes male to look at how a genes on sex chromosome does not separate when it goes through meiosis.
Introduction
Drosophila melanogaster is organism that is very beneficial to genetics. It is commonly known as fruit flies are usually caused by spoiled fruits like banana, apples, and oranges. This organism is a genetic model organism because they have very short life, low maintenances, and gives off numerous off springs for genetics to research on. Therefore in this experiment, D. melanogaster was used to visualize the ideas of Gregor Mendel's and Thomas Hunt Morgan.
Gregor Mendel's was known as father of genetics, and he came up with laws of segregation and law of independent assortment. His law of segregation states that each trait has two alleles, and in gametes there is only one copy of each trait, one from each parent. This law of segregation was tested by setting up monohybrid cross of body color between wild body X ebony body. In the F1 generation all flies were brown body, but in F2 generation brown body was dominant over ebony body, giving the phenotypic ratio of 3:1.
Mendel's second law is the law of independent assortment. He said that inherence for one trait is not dependent on the inherent of another trait because the genes are separate independently. In a dihybrid cross, there are two trait that were crossed, sepia eyes X vestigial wings. These two trait separate independently in meiosis. That means that sepia eyes allele will have no impact on the vestigial wing allele. The phenotypic ratio for a dihybrid is 9:3:3:1.
Morgan is a geneticists who did research on fruit fly. He has a room called the fly room, which he did his research and finding. The finding included was that if certain gene are on the same chromosome they will be inheritance together. He found that eye color was located on the X chromosome. So, in this experiment white eyed females were crossed with red eyed males. Since, females have white eyes they passed on the X chromosome with white eye alleles to their male offspring.
Materials & methods
Obtaining F1 generation
F1 generation for this experiment was provided with one vial for monohybrid between wild type females and ebony males. The monohybrid cross was made for the body color. The second vial was sex-linked between while eyed females and red eyed males, which looked for linkage between sex of fly and eye color of flies. The last vial was dihybrid between sepia eyed females and vestigial winged male, which was tested for linkage of two different traits.
Keeping track
All of the flies were being counted on every other day. The first count was made on the March 19, 2014 and that was also the day F2 generations were made.
Making of F2 generations
In order to make F2 generations, from all three crosses 10 males and 10 females were taken out by anesthetizing them and putting them into a new clean vials that contained Dorsophila growth media. The vials were labeled with the kind of flies in it and also the date they were mated.
Anesthetizing flies
Anethetizing flies is important step in this experiment. This was done by using "fly nap" provided by the instructor. Putting flies to sleep is important in order to take a closer look at the flies. This was done in order to count the F1 generations and to also make F2 generations. In order to put them to sleep, a clean vial, cotton stopper, Petri dish and counting brush was used, "fly nap" and anesthetic wand. Tapping the vial on the desk made flies fall down, then quickly cotton stopper was removed from top and the clean vial was place upside down on top. Then turned both of the vials upside down to let the flies fall into the clean vial than covered both with cotton stoppers. The wand was dipped into the "fly nap" and then opened the clean vial and quickly the as was put inside the vials and closed with stopper. After no flies were moving they were then removed from vial to Petri dish and counted with the brush. F1 generations flies were separated by gender, and F2 were separated by gender and phenotypic variations.
Storing of flies
Flies have to stored in certain temperature, for them to live the regular life span, This flies were stores in the room temperature to give them maximum life span. Increased temperature will result in to decrease in life span and also change the phenotype.
Results
Monohybrid:
F1 Phenotype / Group Data / Class DataFemales / Males / females / Males
Brown body / 95 / 75 / 559 / 630
Ebony body / 0 / 0 / 0 / 0
F2 Phenotype / Group Data / Class Data
Females / Males / Females / Males
Brown body / 60 / 53 / 352 / 480
Ebony body / 24 / 23 / 155 / 161
Df=1 / x2=1.633 / x2=10.948
Table 1.1 Monohybrid cross between Brown body Drosophila and Ebony Body Drosophila.
Sex-Linked
F1 Phenotype / Group Data / Class DataFemales / Males / females / Males
Red eyes / 66 / 0 / 320
White eyes / 0 / 85 / 280
F2 Phenotype / Group Data / Class Data
Females / Males / Females / Males
Red eyes / 40 / 38 / 248 / 272
White eyes / 33 / 40 / 296 / 242
Df=3 / x2=.8674 / x2=6.906
Table 1.2 Sex-linked cross between red eyes female and white eyes male.
Dihybrid
F1 Phenotype / Group Data / Class DataFemales / Males / females / Males
Wild wings/Wild eyes / 0 / 0 / 0 / 0
Wild wings/Sepia eyes / 0 / 0 / 0 / 0
Vestigial wings/Wild eyes / 94 / 85 / 495 / 430
Vestigial wings/Sepia eyes / 0 / 0 / 0 / 0
Group Data / Class Data
F2 Phenotype / Females / Males / Females / Males
Wild wings/Wild eyes / 39 / 42 / 197 / 141
Wild wings/Sepia eyes / 13 / 18 / 52 / 36
Vestigial wings/Wild eyes / 13 / 21 / 54 / 53
Vestigial wings/Sepia eyes / 5 / 4 / 17 / 14
Df=3 / x2=1.457 / x2=4.855
Table 1.3 Dihybrid cross between sepia eyes female and vestigial wing male.
This table shows the results the group and class obtained in both F1 and F2 generation. There also a x2 value, which shows the "goodness of fit" which mean how well the data stood along the hypothesis. According to table 3.2 on page 24 of Experimental Guide, all of the group data is accepted, and all but the dihybrid for class data was rejected. (Barta, 2014)
Discussion
The results for group were more accurate to the hypothesis, that were made with the use of Mendel's laws and Morgan's study on the Drosophila. For monohybrid and dihybrid cross we predicted that monohybrid the ratio would be 3:1 and according to X2 shows that the probability that the deviation is due to chance alone is between 50% to 20, where as for class data it was rejected and reason being that some groups were having problems with their flies growing. The dihybrid cross gave more accurate result than the class did because some groups did not have enough flies growing which made it hard to get more accurate results. According to the X2 calculated the probablity that the result are accurate is between 50% to 80%. Also, the X2 for sex-linked cross shows that there is 80% to 90% probability that the deviation is the to chance alone. The X2 for all the crosses shows how accurate this experiment was as a group rather than the class. The class X2 values should have been more accurate but because some groups were having problems with their Drosophila giving more off springs.
References
Barta JL(2014) BIO 3010 Experimental Guide. Livonia MI: Madonna University Press.
Appendix
Group:
SEX-LINKEDPHENOTYPE / O / E / O-E / (O-E)2 / (O-E)2/E
Red eye male / 38 / 37.5 / 0.25 / 0.0625 / 0.0016
red eye female / 40 / 37.5 / 2.25 / 5.0625 / 0.1341
White eye male / 40 / 37.5 / 2.25 / 5.0625 / 0.1341
white eye female / 33 / 37.5 / -4.75 / 22.562 / 0.5976
Total / 151 / 151 / X2=.8674
MONOHYBRID
PHENOTYPE / O / E / O-E / (O-E)2 / (O-E)2/E
Wild / 113 / 120 / -7 / 49 / 0.408
Ebony / 47 / 40 / 7 / 49 / 1.225
Total / 160 / 160 / X2=1.633
DIHYBRID
PHENOTYPE / O / E / O-E / (O-E)2 / (O-E)2/E
Wild wings/Wild eyes / 81 / 87.19 / -6.19 / 38.31 / 0.439
Wild wings/Sepia eyes / 31 / 29.06 / 1.94 / 3.76 / 0.13
Vestigial wings/Wild eyes / 34 / 29.06 / 4.94 / 24.4 / 0.839
Vestigial wings/Sepia eyes / 9 / 9.69 / -0.69 / 0.4761 / 0.0491
Total / 155 / 155 / X2=1.457
Class:
SEX-LINKEDPHENOTYPE / O / E / O-E / (O-E)2 / (O-E)2/E
Red eye male / 272 / 264.5 / 7.5 / 56.25 / 0.2126
red eye female / 248 / 264.5 / -16.5 / 272.25 / 1.029
White eye male / 42 / 264.5 / -22.5 / 506.25 / 1.913
white eye female / 296 / 264.5 / 31.5 / 992.25 / 3.751
Total / 1058 / 1058 / X2=6.906
MONOHYBRID
PHENOTYPE / O / E / O-E / (O-E)2 / (O-E)2/E
Wild / 760 / 807 / -47 / 2209 / 2.737
Ebony / 316 / 269 / 47 / 2209 / 8.211
Total / 1076 / 1076 / X2=10.948
DIHYBRID
PHENOTYPE / O / E / O-E / (O-E)2 / (O-E)2/E
Wild wings/Wild eyes / 338 / 317.25 / 20.75 / 430.56 / 1.35
Wild wings/Sepia eyes / 107 / 105.75 / 1.25 / 1.56 / 0.014
Vestigial wings/Wild eyes / 88 / 105.75 / -17.75 / 315.06 / 2.079
Vestigial wings/Sepia eyes / 31 / 35.25 / -4.25 / 18.06 / 0.512
Total / 564 / 564 / X2=4.855