Drosophila Lab: Sex-Linked Cross

Drosophila: Sex-Linked Cross Lab Report
40 Points
This lab report may be done in pairs or individually (not in groups of four!). For the report
format, follow the guidelines in the Lab Report Rubric document (posted on eboard if you
need it).
Background for the lab
P1: females were XwXw (white-eyed) and males were X+Y(red-eyed is dominant)
We then crossed the F1’s and ten days later counted the F2’s. The results of those
counts are posted here:
Group name:
F2 #’s: Sex and Eye-Color
For this assignment make the following changes.
1. Purpose of lab and w hat you hoped/expected to learn.
2. For background paragraph choose a related topic and discuss it. Possibilities:
Morgan and his understanding of X-Linked traits, summary on inheritance
patterns for X-Linked traits (how does it work?), some common X-Linked traits
of the fruit fly (Drosophila melanogaster), an exploration into other organisms
that have a similar X Y system of chromosomal arrangement, an investigation if
there are any Y-linked traits in humans (does the male Y have any genes that are
not found on the X?), some unusual X-Linked traits in humans (besides red-green
color blindness and hemophilia), etc.
3. Hypothesis—we didn’t state this before hand, but by knowing the genotype of
the P1’s you should be able to figure out what the expected genotypic ratios
would be for the F2’s. Go ahead and figure that out and form it into a hypothesis
for this section.
In general, cover the following topics:
a. Tips on sexing fruit flies
b. When and why the P1’s had to be “dumped” before the F1’s emerged
c. What you had to do to cross the F1’s to get F2’s
d. What should be done with the flies after counting them?
Data and Analysis:
 Make a sketch of both a male and a female fly. Try and show the key details we
used for the sexing aspect. Don’t get hung up in the anatomy of the fly too much!
Use the internet for resources or see me for some fly pictures.
 Follow the general rules on illustration as spelled out in the Lab Report Rubric.
Data table
 Include one using the data I posted. You may condense it and simply use the sum
for each sex/eye-color. Make sure to label it properly.
 Write out your computations for Chi-square analysis of the data. This may be handwritten if that’s easier for you. Leave space in the data section to write it in (don’t
just attach it to the back of the report).
1. Discuss and explain all of your results.
2. Results…take your data and run a Chi-Square analysis to see if our data “fits” the
expected ratios. (what would be the degrees of freedom for this lab? _____)
Show your computations and then put them into common English so that everyone
could understand it.
3. Hypothesis…supported or not supported?
4. Application—SKIP THIS SECTION
5. Shortcomings…What kind of things went wrong? I can think of several right off
the bat. One is the goop factor of the culture medium (that’s usually due to
improper mixing!). Take time to “relive” the lab exercise and point out the
obvious. Make sure to post recommendations on how to eliminate these issues.
6. Website references…for your research in the Purpose section. Feel free to site
our text as a resource if you use it.
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