Solved by a verified expert:FLY-LAB PART II (Assignments 1-3)
Log onto Bioline ( The
username is (ashlandtest5) and the password is (eagles2013). Then Click on
FLYLAB. the Flylab page will load. Click
START LAB. The Applet will load and this
is where you will design your flies and perform your crosses. Please follow the
directions in the assignments (these instructions are also online). For your lab report, you will need to provide
answers to the questions in red color (IN
BOLD). Be certain to give complete answers to the questions.

Assignment #1:

The genetic
phenomenon called epistasis occurs when the expression of one gene
depends on or modifies the expression of another gene. In some cases of epistasis, one gene may completely mask
or alter the expression of another gene. Perform the following crosses to study
examples of epistasis in Drosophila.

Design and perform a cross between a female fly with vestigial wing
size and a male fly with an incomplete wing vein mutation. Carefully study
the phenotype of this male fly to be sure that you understand the effect
of the incomplete allele.

What did you observe in the F1
generation? Note: It may be helpful to click up and
down in this display box to closely compare the phenotypes of the F1
and P generations.

Was this what you expected? Why or why
not? Once you have produced an F1 generation, mate F1
flies to generate an F2 generation.
Study the results of your F2 generation and
then answer the following questions.
Which mutation is epistatic? Is the
vestigial mutation dominant or recessive? Determine the phenotypic ratio that
appeared in the dihybrid F2 generation, and use chi-square analysis
to accept or reject this ratio.

Perform another experiment by mating a female
fly with the apterous wing size mutation with a male fly with the radius
incomplete vein structure mutation. Follow this cross to the F2

Which mutation is epistatic? Is the
apterous wing mutation dominant or recessive?

Assignment #2:

Mendel’s law of
independent assortment applies to unlinked alleles, but linked genes–genes
on the same chromosome — do not assort independently. Yet linked genes are not
always inherited together because of crossing over. Crossing over, or homologous
recombination, occurs during prophase of meiosis I when segments of DNA are
exchanged between homologous chromosomes. Homologous recombination can produce
new and different combinations of alleles in offspring. Offspring with
different combinations of phenotypes compared with their parents are called recombinants.
The frequency of appearance of recombinants in offspring is known as
recombination frequency. Recombination frequency represents the frequency of a
crossing–over event between the loci for linked alleles. If two alleles for
two different traits are located at different positions on the same chromosome
(heterozygous loci) and these alleles are far apart on the chromosome, then the
probability of a chance exchange, or recombination, of DNA between the two loci
is high. Conversely, loci that are closely spaced typically demonstrate a low
probability of recombination. Recombination frequencies can be used to develop
gene maps, where the relative positions of loci along a chromosome can be
established by studying the number of recombinant offspring. For example, if a
dihybrid cross for two linked genes yields 15% recombinant offspring, this
means that 15% of the offspring were produced by crossing over between the loci
for these two genes. A genetic map is displayed as the linear arrangement of
genes on a chromosome. Loci are arranged on a map according to map units called
centimorgans. One centimorgan is equal to a 1% recombination frequency. In this
case, the two loci are separated by approximately 15 centimorgans. In
Drosophila, unlike most organisms, it is important to realize that crossing
over occurs during gamete formation in female flies only. Because crossing over
does not occur in male flies, recombination frequencies will differ when
comparing female flies with male flies. Perform the following experiments to
help you understand how recombination frequencies can be used to develop
genetic maps. In the future, you will have the opportunity to study genetic
mapping of chromosomes in more detail using PedigreeLab.

To understand how recombination frequencies
can be used to determine an approximate map distance between closely
linked genes, cross a female fly with the eyeless mutation for eye shape
with a male fly with shaven bristles. Both of these genes are located on
chromosome IV in Drosophila. Testcross one of the F1 females to
a male with both the eyeless and shaven bristle traits. The testcross
progeny with either mutations or neither mutation (wild-type) are produced
by crossing over in the double heterozygous F1 female. The
percentage of these recombinant phenotypes is an estimate of the map
distance between these two genes.

Draw a map that shows the map distance
(in map units or centimorgans) between the locus for the shaven bristle allele
and the locus for the eyeless allele.

To understand how recombination frequencies
can be used to determine a genetic map for three alleles, mate a female
fly with a black body, purple eyes, and vestigial wing size to a wild-type
male. These three alleles are located on chromosome II in Drosophila.
Testcross one of the F1 females to a male with all three
mutations. The flies with the least frequent phenotypes should show the
same phenotypes; these complementary flies represent double crossovers.

What is the phenotype of these flies?
What does this tell you about the position of the purple eye allele compared
with the black body and vestigial wing alleles? Sketch a genetic map indicating
the relative loci for each of these three alleles, and indicate the approximate
map distance between each locus.

Assignment #3:

Group Assignment
Work in pairs to complete the following assignment.
Each pair of students should randomly design two separate dihybrid crosses of
flies with mutations for two different characters (ideally choose mutations
that you have not looked at in previous assignments) and perform matings of
these flies. Before designing your flies, refer to the Genetic Abbreviations
chart in FlyLab for a description of each mutated phenotype. Or view the
different mutations available by selecting a fly, clicking on each of the
different phenotypes, and viewing each mutated phenotype until you select one
that you would like to follow. Once you have mated these flies, follow
offspring to the F2 generation.

For each dihybrid cross, answer the following questions. Perform
additional experiments if necessary to answer these questions.

Which of these traits are dominant and which
traits are recessive?
Are any of these mutations lethal in a homozygous
fly? Which ones?
Are any of the alleles that you followed
sex-linked? How do you know this?
Which alleles appear to be inherited on
If any of the genes were linked, what is the
map distance between these genes?

For at least one of your crosses, attempt to perform the cross on
paper using a Punnett square to confirm the results obtained by FlyLab.
Ask another pair of students to carry out one of the crosses that
you designed. Did they get the same results that you did in the F1
and F2 generations? Did they develop the same hypotheses to
explain the results of this mating as you did? Explain your answer.
Once you have completed this exercise, discuss your results with
your instructor to determine if your observations and predictions were accurate.