Biology Homework

Running head: BIOLOGY LAB PROJECT 1

BIOLOGY LAB PROJECT 4

Introduction

Drosophila melanogaster is a species of fly in the family drosophilidae. The common name for Drosophila melanogaster is fruit fly or vinegar fly (Capy, Gibert & Boussy, 2004). The drosophila is a species widely used for biological research in studies of genetics, physiology, microbial pathogenesis, and life history evolution. It has been used to study genetics for over 100 years. D. melanogaster was one of the first organisms used for genetic analysis and is still widely used today. The drosophila is largely used for research study because it is an insect that is easy to take care of and lays many eggs, which gives us the opportunity to have many flies to study. Also, fruit flies can create a complete generation in about ten days thus allows several generations to be produced and studied within a few weeks (Regan, 2014). The average life of a fruit fly in optimal temperatures is 40 to 50 days. The life of Drosophila melanogaster depends on the weather temperature. For example, D. melanogaster’s lifespan is around 30 days at 29˚ C, 84˚ F and the lifespan decreases with a decrease in temperature. Drosophila’s eggs can hatch after 12–15 hours. The female can mate with the male after 8 to 12 hours after hatching. Nowadays, most genetics scientists prefer to use the Drosophila melanogaster flies because they can study different generations in a short period of time.

In the genetics lab, we determine the mode of inheritance of phenotype mutant and wild type. We cross wild type males with female mutants. Also, we cross mutant males with wild type females to determine the genetic changes in both generations. The wild type flies have red eyes phenotype and long (normal) wings. On the other hand, mutants have white eyes and short wings. These observations are made after observing the first and second generations for both cross and wild type breeds and then comparing the observable change between them. In this course, we make several crosses between flies from wild-type and mutant phenotypes to show the mode of inheritance of the genes in Drosophila Melanogaster.

Methods and Materials

In this lab we used fruit flies and we examined them by putting them under the microscope. We also use FlyNap by to make the flies sleep for a mount of time while we viewing them. In order to use the FlyNap, first we transfer the flies to an empty vial and we do that by place the vial that we want to transfer immediately over the opening of the empty vial, so by this we will not allow the flies to escape from our vial. After they have been transfer to the new vial we place a small FlyNap brush and wait for a while until they all sleep. When they all sleep we put them in a small plate. At this time, we will be able to put them under the microscope and we use a paintbrush to move and look at the flies. Under the microscope we can easily determine the phenotype and the sex for each fly. We carefully record our observation and return the flies into their vial.

Once our parental generation had been examined and recorded, we were ready to set up our first cross to generate our F1 generation. In each cross, we ideally needed between 3-5 flies of each sex to produce the best results. Our first cross was between wiled type males and mutant females. Also, the other cross was between wiled type females and mutant males. These cross required us to have virgin females for both crosses to be sure they do not mate with other and to have a good result. To obtain virgin females, we emptied our original stock vials by anaesthetizing any living flies in these vials and disposing of them in the Fly Morgue. This ensured that any female flies collected 8-10 hours after emptying these vials would be virgin flies.

One of our F2 cross was again between wiled type males and mutant females. The other one was between wiled type females and mutant males. The F2 cross must be from the resulting of F1 progeny. In F2 cross virgin females are required, but this time it is from F1 generation. We obtained these virgin flies in the same manner; we emptying the F1 generation vials first in the morning early from any live flies. Then, we come in the afternoon after 8 to 10 hours to collect the virgin females. The results of these crosses provided us with ample information to come to a conclusion on the mode of inheritance of the mutant body color phenotype.

Preparing Fly Media and Vials

For the initial and subsequent crosses, fly media was prepared and placed into each vial as a food source for the flies. This was done by placing a scoop of 4-24 instant culture medium along with an equal amount (a scoop) of water into the bottom of each vial. We allowed the water to absorb into the medium for a few minutes before placing the flies into the vial. A few grains of yeast were also sprinkled into the medium to encourage the female to lay her eggs.

Each vial was then labeled with our group name as well as the contents of the vial. All of the vials were then secured together with a rubber band and placed in the incubator located in the lab. The incubator is maintained at 23 degrees Celsius with a 12-hour day/night cycle. Our vials were checked frequently and maintained properly during the course of the lab.

Results and mothed:

To know if our results did support or hypothesis or not we used the Chi square to test our data. The Chi square can be calculated by using this formula (expected – observed) ^2 / observed). After we calculate the Chi square we get the P-value which telling us if we should accept or reject our hypothesis. Also we need to determine the degree of freedom by using this equation n-1 here n in this situation is the number of possible phenotypes of the progeny. If our p-value become more than .5 we rejected the hypothesis if it is less we accept it.

Results:

Mutant Female x Wild Male

F1 = 21 offspring, 7 males, 14 females - all wild 

F2 = 16 offspring, 4 males (all dark), 12 females (10 wild, 2 dark)

Wild female x Mutant Male

F1 = 24 offspring, 11 males (10 wild, 1 dark), 13 females (all wild)

F2 = 19 offspring, 10 males (3 dark, 7 wild), 9 females (8 wild, 1 dark)  4 dark, 15 wild

Please do chi square for this data. Our trait is autosomal and our mutation is dark body.

References

Capy, P., Gibert, P., & Boussy, I. (2004). Drosophila melanogaster, Drosophila simulans: So

similar, so different. Dordrecht: Kluwer Academic.

Regan, J. L. (2014). Drosophila melanogaster: Genome evolution, behavior and economic

importance. New York : Novinka.