Fruit Flies
Caleb Stone
IntroductionThe experiment conducted was to determine which trait was recessive, and which
trait was dominant in the Drosophila melanogaster, more commonly known as the fruit
fly. We were also asked to determine if the probability of the traits, matched the reality of
the outcome of the crosses. Each student was given several vials of both apterous (nonwinged) and wild (winged) flies to experiment with. After a large amount of virgins were
collected from both the apterous and wild vials, crosses were made between the two.
After the first cross was made, the parents were removed, sorted, and then placed into F1
vials. This experiment was carried through into the F2 generation. Punnett Squares were
instrumental in determining the probability of the outcome of the traits.
Methods and Materials-
Various methods and materials were used in the experiment involving the
Drosophila melanogaster fruit fly. The first step of the experiment was to sort the flies
into a parent generation which will henceforth be referred to as the P1 generation. The
flies were placed into vials with approximately two to three grams of fly medium and
twelve to fifteen milliliters of water. In most of the students’ experiments, five to six
granules of yeast were also used; however in one personal experiment it appears that the
yeast was detrimental to the health of the fruit flies and was removed from the equation.
The vials containing the flies were stored in a room with a temperature around seventy
degrees Fahrenheit. If the temperature dropped below fifty degrees Fahrenheit, the flies
Fruit Flies
Caleb Stone
would die off rather quickly, usually within twenty-four hours. The flies were given to
all students in mid-October 2012 and most students, all but one in fact, finished around
mid to late December of 2012. Students were issued a two ounce bottle of FlyNap and
three wands with which to dispense it and to assist in sorting the flies into male and
female vials. After the parents were removed from the vials, the larvae was allowed to
hatch and then sorted. The males of this generation, whether apterous or wild, were
removed and humanely disposed of. The females were kept alone for 12 days with other
virgin females so as to ensure their virgin status. They are then saved to be coupled with
the opposite phenotype males later in the experiment. Once twenty virgin females were
collected, five males of the opposite trait were added into the vial with them, thus
creating the F1 generation. A total of 200 F1 generation flies had to be collected from the
crosses; apterous females by wild males, and wild females by apterous males. The F1
generation was placed in vials of 50 flies apiece and labeled F1 x F1. Once larvae
appeared onto the side of the vial, the parents were removed. Once the larvae hatched
into the F2 generation, they were sedated with the FlyNap and sorted according to
whether they were wild or apterous. Flies with “dumpy” wings were counted as wild.
Results and DiscussionF1 Generation
In the experiment, Punnett Squares and Bar Graphs are used to show and compare
the results of the probability of the outcome of the crosses, and the reality of the outcome
of the crosses. The total amount of flies collected from the F1 generation was 187 write
82 showing Apterous trait. The probability of the flies being wild was 4:0 (100%) which
Fruit Flies
Caleb Stone
is a large discrepancy to the reality. Though the probability would have the wild
population dwarf the apterous population, in reality the apterous population was nearly
as large as the wild population.
F1 PROBABILITY
F1 REALITY
Phenotypes
Apterous
Apterous
Wild
Phenotypes
Wild
0%
0%
20%
40%
50%
100%
150%
60%
F1 PROBABILITY
W
W
w
Ww
Ww
w
Ww
Ww
F2 Generation
The F2 generation of the fruit flies consisted of the offspring of the F1 generation. The
flies were not sexed, only sorted into vials based on whether they possessed the apterous
or wild trait. A relatively small total of 74 F2 generation flies were collected in this
experiment, the reason being the student suffered many setbacks throughout. The wild
trait was found in 56 of the flies, while 18 were apterous. The ratio of the F2 generation
genotype was 1:2:1 and the phenotype was 3:1.
Fruit Flies
Caleb Stone
W
w
W
WW
Ww
W
Ww
Ww
F2 probability
F2 REALITY
F2 PROBABILITY
Flies
Phenotypes
Phenotypes
Apterous
Flies
Wild
Apterous
0%
50%
100%
Wild
0.00%
20.00%
40.00%
60.00%
80.00%
Total Flies
In conclusion, a mistake was obviously made somewhere in the F1 generation.
This hypothesis is based on the fact that the F1 generation contained a great number of
apterous flies while the F2 generation contains a much smaller amount. It is hypothesized
that hypothesize that either the F1 vial was left alone to breed too long and what was
presumed to be only F1 generation flies was actually a mixture of F1 and F2 thus
increasing the probability of apterous flies which then carried the trait further down the
line. The other possibility is that perhaps a male was erroneously placed into a virgin vial
Fruit Flies
Caleb Stone
and said male carried the apterous gene thus impregnating virgin flies with offspring also
carrying the gene.