openlab.citytech.cuny.edu€¦ · Web viewLab report #4 New York City College of Technology Abstract Drosophila melanogaster is a fruit fly used to examine how phenotypes are passed

Inheritance patterns for Drosophila melanogaster Asma AkamLab report #4

New York City College of Technology

AbstractDrosophila melanogaster is a fruit fly used to examine how phenotypes are passed down

from parent to offspring. A cross between female wild type and white eyed male flies were made. The allele for eye color is found on the X chromosome. A dominant trait is expressed over a recessive trait.

IntroductionGregor Mendel discovered two laws of inherence, the law of independent assortment and

law of segregation. In this study we examined how phenotypes were passed down in generations from parent to offspring by using Drosophila melanogaster, a common fruit fly. The study was conducted over several weeks to examine how traits such as eye color and body color are passed from parent to offspring. In this experiment wild type flies have red eyes, sepia flies have brown eyes and long wings, and vestigial flies have red eyes and short wings. A cross between female red eyes and white eyed male flies were made. Mendel discovered that F1 generations have recessive traits from their parents that are not present and that in F2 generations the recessive traits reappear (Wynn, 2007). In relation to fruit flies red eyes are dominant over white eyes. These traits are expressed due to sex linkage, which illustrates that traits are expressed depending on which X chromosome is carrying the trait. Males have only one X chromosome, while females have two X chromosomes.

MethodsIn lab we examined inheritances patterns of Fruit flies (Drosophila melanogaster), over

the course of a few weeks. First we set up an F1 cross, each group was given specific types of flies to cross. Our cross was wild-type female flies with white eyed male flies. In order to cross the flies, we had two vials one with flies and one empty. We lightly tabbed the tube with the flies on the table to bring the flies down. Then we inverted the second empty vial on top the fly vial to allow the flies to move to the empty one. After the flies migrate to the empty vial we placed a chloroform swab for a couple of second until the flies slept. On a petri dish we observed and separated the flies based on their gender and desired traits, three females and three males. In an empty vial we set up the medium, one cup of medium and one cup of water with 4-7 grains of yeast and mixed it, until it solidifies. We placed the flies we separated into the vial horizontally. The following week we took out the F1 flies and left the larva, which was our F2 generation. In the following week we observed the F2 anesthetized flies in a petri dish and recorded our results based on their gender and phenotype. After the flies were placed in alcohol to dispose of them.

ResultsA cross between female wild type XR XW and white eyed male XW Y flies was made

and recorded on table 1. Table 2, illustrates a cross between sepia (recessive) and wild type (dominant) flies. The punnet square illustrated in figure 1, demonstrates the percentage for each trait.

DiscussionDrosophila melanogaster is a ‘model organism’ used to understand the inheritance pattern

of phenotypes passed down from parents to offspring. My group was first assigned a cross between vestigial flies with Sepia flies, unfortunately due to errors in our experiment the flies did not survive. A cross between female wild type and white-eyed male flies and a cross between Sepia flies and wild type flies were observed. In our experiment many errors could have affected

our result such as a small sample size and not being able to clearly identify genders. The experiment was meant to demonstrate sex linkage. In F1 generation if the females were homozygous for white eyes and the males were red eyed, there would have been a clearer distinction on how traits were passed down. In that scenario, in the F2 generation all the females would have red eyes due to the dominant red eye traits passed from the father and all the males would have white eyes from the mother. The same would be true with the sepia and wild type cross, sepia being recessive.

Table 1: Cross between wild type females and white eyed males

Phenotype (eye)

Females Males

White 10 18

Red 12 14

Total: 54 flies

Table 2: Cross between sepia and wild type flies

Phenotype (eye)

Females Males

Brown (Sepia) 9 17

Red 16 17

Total: 59 flies

Table 3: Punnet square for wild type females XR XW + white eyed males XW Y

XW Y

XR XR XW XR Y

XW XW XW XW Y

Females Red eyes = ¼ or 25%Females White eyes = ¼ or 25 %Males Red eyes = ¼ or 25%Males White eyes = ¼ or 25

Figure 1: F2 generation of Drosophila melanogaster

Reference

Wynn, J. (2007). Alone in the Garden: How Gregor Mendel's Inattention to Audience May Have Affected the Reception of His Theory of Inheritance in "Experiments in Plant Hybridization" Written Communication, 24(1), 3-27. doi:10.1177/0741088306296024