DROSOPHILA LAB II
To discover how certain traits are inherited in Drosophila.
Drosophila medium, Drosophila cultures, Anesthetizer, brush, dissecting scopes, infinite
A. ISOLATING VIRGINS:
A female Drosophila can store and use sperm from a single insemination for the major
portion of her reproductive life. Thus, it is necessary to select virgin females
for genetic crosses. The old double standard holds for Drosophila also, therefore
it is not necessary that the males be virgins.
Older males will mate with newly hatched females. Therefore it is essential that
all adult flies be cleared from the vial that is being used to hatch virgin females.
It is a good idea to keep these flies as part of your backup culture rather than
When pupae are ready for hatching they will darken. Clear all adult flies from the
vial as late in the evening as feasible. Flies tend to hatch in the early morning
in the greatest numbers. Check the vial within 10 hours of clearing and remove and
sex any flies present. Begin your 10 hour timing again and continue to remove and sex
the flies that hatch within ten hours. If you will devote yourself to this time
schedule for one or two days you should be able to get all the virgins you need.
Remember that insuring virginity and correct sexing of these flies is crucial to the success
of your experiment.
B. MAKING CROSSES:
The strains of flies we are using are all true breeding so are assumed to be homozygous.
You will be concerned only with the traits listed on the vial for your flies. +
is used to represent the wild type flies.
Using procedures studied for isolating and identifying flies, select at least 3 virgin
females of the type needed fo
r the cross assigned to you. Place these virgin flies
and at least three males of the type needed for the cross assigned to you in a vial
with fresh culture medium. You may add these flies one or two at a time if necessary.
You do not have to add them all at once. For instance, if you get only one virgin
female you may place her in the vial alone. However, try to limit the number of
times you must anesthetize your flies as this sometimes decreases viability.
Be sure you label the vial as your P 1 cross and record all your data in your log
book. Locate a group that is making the reciprocal of your cross. For example, if
your cross a wild female with a white-eyed male the reciprocal would be a white-eyed
female with a wild male.
Observe both crosses daily and record your observations in your log book. After about
7 or 8 days remove the parent flies. Anesthetize them and place them in the morgue.
We will have a wake and mass burial later. Flies of the F1 generation will begin
to appear about 10 days after mating. After several flies have appeared, anesthetize
them, identify them as to characteristic and sex, record your results and place
them in a new vial with fresh medium. This should be labeled as your F1 cross.
Since all members of the F1 are the same it is not necessary to obtain virgins. You should
cross at least 6 females and 6 males. The numbers are not critical, however, the
more flies you cross the more flies you will get in your F2 and the better your results
will be. Continue to identify, count and record the flies that hatch out in your F1
vial until no more flies emerge.
Observe the F1 vial daily and record your results. As these flies hatch, anesthetize,
identify, and count them. Remember to note the characteristics and sex of each fly.
Once the flies are counted they may be placed in the morgue. Check with the group
that did your reciprocal cross and record their total counts for each generation.
Determine the F2 phenotyp
ic ratios for both crosses and form an hypothesis as to
the manner of inheritance. Calculate the X2 values for each of the crosses.
IV. LAB REPORT:
This will be a formal lab report and will contain the following:
Page 1 Cover page- Name, date, Title of Lab
Page 2 Abstract- Brief summary of the rationale and the experiment.
Page 3 Hypothesis- Even though you have included this in your abstract, please
place it on a separate sheet and label it your hypothesis.
Page 4 Methods and materials- a brief summary of the procedures used. You may
assume that your reader is familiar with basic techniques and need not give details
of making medium, identifying flies, etc.
Page 5 Data charts for F1 and F2 for your cross and for the reciprocal cross.
Page 6 Conclusion- either support or refute your hypothesis using your X2 data.
If necessary, offer a new hypothesis or cite specific errors in your procedures
to explain your data deviations.