Mutations of Drosophila - Lab Report Example

? Drosophila Crosses Report Introduction This experiment was based on the study and analysis of drosophila, the common fruit fly as a model organism for genetic studies. Benefits involved in studying drosophila were that it is easily cultured in the labs, it has shorter generation time, and it can as well produce several offspring. Life cycle of drosophila, from the egg stage to adult stage lasts for ten days at room temperature. Eggs are laid and hatched into first instars larvae. The larvae feed voraciously on the culture medium provided, and undergo several instars stages and finally the third instars larvae crawls up the sides of the bottle away from the culture medium. At this stage they stop and their larval cuticle hardens to form a dark brown pupa. Metamorphosis then takes place during this pupal stage, and larvae tissues disintegrate and restructure to form an adult fly within the pupal case. Adult fly thereafter emerge from the pupal case immediately the metamorphosis stage is completed. Wings then expand and dry up, the abdomen becomes curved while the body color becomes darker. Distinctions between male drosophila from female drosophila i. The male drosophila has a small, densely packed tuft of bristles called sex comb on the first pair of appendages, and a fringe of black bristle on the forelegs ii. Tips of the abdomen are elongated and somehow pointed in female drosophila and more rounded in male drosophila. iii. Abdomen of the female drosophila has many segments (7 in number), as compared to male drosophila with only five (5) segments. Diagrammatically represented as below: Drosophila Crosses Genetic notation In this case study, the normal fly was categorized as a wild type while the other type of fly exhibiting a phenotypic mutation was categorized as mutants. Mutants were given names that denoted the type of mutation the fly exhibits. For instance, the mutant ebony had a much darker body than the wild type fly. Construction of a chromosome map in Drosophila A chromosome map was constructed form three breeding results using testcrosses that involved flies heterozygous at more than one locus, and taking into account the frequencies of crossover between the loci. Three loci on the second chromosome, an auto some, was chosen to for this experiment for the effect of body color, wing size, and eye color. Each locus had a wild type and mutant allele whose traits were as listed on the table below: Characteristic Chromosome Genes Body Color X Y = yellow body W= white eye V = vermilion (bright orange-red eye) M = miniature wings (wings go only to tip of abdomen) B = bar eyes (Semi-dominant in female) narrow eye plus some double x-chromosomes mutants Wing shape 2 Ap = apterous (wingless) Dp = bumpy wings Vg = vestigial wings Bw = brown eye (dark red eye) Eye Color 3 Se = sepia eye (dark red eye) E = ebony body (dark body) Cross 1 Punnett square F1s CnBw Cnbw cnBw cnbw CnBw CnCn, BwBw CnCn, Bwbw Cncn, BwBw Cncn, Bwbw Cnbw CnCn, Bwbw CnCn, bwbw Cncn, BwBw Cncn, bwbw cnBw Cncn, BwBw Cncn, Bwbw cncn, BwBw cncn, Bwbw cnbw Cncn, Bwbw Cncn, bwbw cncn, Bwbw cncn, bwbw From the table above, a di-hybrid cross of each of the F1 parents produced four different gamete types contributing to 16 (4x4) possible offspring combinations. Because of the two different traits shown in the table above, there is complete dominance and separate independent of each other, and the expected genotypic and phenotypic rations from this analysis calculated is to be 9:3:3:1. It was examined that the inheritance of eyes color and wing shape by crossing two pure breeding straits of Drosophila melanogastern. Phenotypes of the progeny are as shown below: Phenotypes Number of progeny Males Females Total Brown eyes 46 29 75 Red eyes 29 10 39 Orange eyes 18 7 25 139 Cross 2 DpX^wm DpX^wm dpX^wm dpX^wm DpX^wm DpDp,X^wmX^wm DpDp,X^wmX^wm Dpdp,X^wmX^wm Dpdp,X^wmX^wm DpY DpDp, X^wmY DpDp,X^wmY Dpdp, X^wmY Dpdp, X^wmY dpX^wm Dpdp,X^wmX^wm Dpdp,X^wmX^wm dpdp, X^wmX^wm dpdp,X^wmX^wm dpY Dpdp, X^wmY Dpdp, X^wmY dpdp, X^wmY dpdp,X^wmY Results for F2 of the parental cross dominates that the wild type allele is dominant allele for sepia, vestigial flies being 9.3:2.8:2.7:1. This represented a minor difference from the 9:3:3:1 ratio as was expected for the simple di-hybrid cross. Results of this punnette square test suggest that the experimental data actually had a very negligible difference, as may be a result of minor sample scale scored from the cross. The phenotype of the F1, progeny therefore confirmed that the allele for wild type Dpdp, X^wmX^wm is dominant to the allele for sepia, DpDp, XX, with the ratio of being 9.3:2.8:2.7:1 illustrated in F2. This experiment is hence a strong confirmation of the Mendel’s Law of Independent Assortment. Phenotypes Number of progeny Males Females Total White mins 42 0 75 Duncy Red 33 45 39 Red mini 6 0 25 126 Cross 3 X^v E X^v e X^v E X^v e X^v E X^vX, EE X^vX^vEe X^v X^v EE X^v X^v Ee X^v e X^vX^vEe X^vX^vee XXEe X^vX^v ee YE X^vXEE XYEe XYEE X^vXEe Ye X^vYEe X^vYee X^vYEe X^vYee Based on these results obtained from the experiment, in the first cross male Drosophila dominated with red eyes and brown bodies, and X-linked inherited deficiencies occurred most frequently in males since they only have a single chromosome. Female flies carry mutant gene, as shown in cross 2, but when crossed with normal male, a ratio of 1:1:1:1 was realized in the F2 offspring. Reason for this is that possible combinations of red eyes and sex are possible and the red eye trait can be carried over to female whenever F1 females are crossed with red eye males. Phenotypes Number of progeny Males Females Total Red eyes, black body 4 2 6 Orange eyes, black body 3 2 5 Red eyes, brown body 10 8 18 Orange eyes, brown body 5 6 11 40 References Radlick, L. (2011). Analyzing Mutations of the Eye Pigments In Wild and Mutant Strains Of Drosophila. BIOL 1010 Read More