Fruit Fly
Genetics
Chromosome Theory of Heredity
Found that genes are located on
chromosomes
Discovered Sex-Linkage
Worked with Drosophila
Nobel Prize for Physiology /
Medicine in 1933.
Thomas Hunt Morgan
Why Drosophila?
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Short Generation Time
Easy to Maintain
4 large chromosomes
Easily identifiable
Markers (mutant phenotypes)
CHROMOSOMES
Female
Male
XX /XY
---Sex---
II
III
IV
-----------Autosomal-----------
Sex -chromosomes responsible for determining sex
of an individual
Autosomal- chromosome that is not directly
involved in determining sex.
Sexing adult flies
Terminology: Phenotypes
Wild type- the normal or most common phenotype in a
population.
Mutant Phenotype- traits that are alternates to the wild
type. Changes due to mutations in the wild type.
wt
ebony
white body
Example Phenotypes
Wild
type
Ebony
body
Vestigial
wings
Curled
wings
Wild type vs. ‘white eye’
phenotype
WT
White eye
mutant
Nomenclature
Autosomal Genes (use + for wt allele)
Use the following format when performing crosses:
Genotype
Phenotype
+/+
vg / +
wt (homozygous)
wt (heterozygous)
vg / vg
+___
mutant
wt (homozygous or
heterozygous)
Morgan suggested that this was due to an exchange of
equal chromosome segments during synapsis in meiosis
which he called crossing over.
Autosomal Gene Nomenclature
Wild-type genes located on autosomal
chromosomes are donated “+” by
convention (Each allele is represented and
is seperated by a “/”)
Genotype
+/+
vg / +
vg / vg
Phenotype
wt (homozygous)
wt (heterozygous)
mutant
Monohybrid Cross
Cross breeding
organisms while
tracking only
one trait.
Example Monohybrid Cross
++
(Wildtype)
x
vgvg
(Vestigial)
F1 Genotypes
F1
vg
vg
+
+vg
+vg
+
+vg
+vg
Phenotypic Ratio: 4:4 wt
Genotypic Ratio: 4:4 +vg
We then cross two F1 progeny:
+vg
(heterozygous)
x
+vg
(heterozygous)
F2 Genotypes
+
vg
+
++
+vg
vg
+vg
vgvg
F2 Phenotypic Ratio: 3 wt: 1 vg
Genotypic Ratio: ¼ ++, 2/4 +vg, ¼ vgvg
In a sex-linked cross, the principles are similar but the
notation differs. Instead of showing the alleles on
the X or Y chromosome, simply use the symbol for
the gene that is on the X, for example:
w+w+ is a female red-eyed fly.
w≠ is a hemizygous white-eyed male.
The (≠) denotes the Y chromosome, which in
Drosophila carries only a few genes. Keep in mind
that w+ is completely dominant to w, and that this is
a case of complete sex-linkage.
As an example of an X-linked cross , we will look at goggle-eye (unusually
prominent eyes), an X-linked recessive trait (g) in Drosophila:
As an example of an X-linked cross , we will look at goggle-eye (unusually
prominent eyes), an X-linked recessive trait (g) in Drosophila:
Example Dihybrid Cross
++/++
(Wild type)
x
bb/vgvg
(Black vestigial)
Dihybrid crosses involve manipulation and analysis of two traits
controlled by pairs of alleles at different loci. For example, in the cross
ebony body x vestigial wing
e is ebony body color
e+ is wild-type body colour
vg is vestigial wing shape
vg+ is wild-type wing shape:
F2
F2
Morgan’s fruit flies…
F1
Cambell, Reece, Taylor, Simon, and Dickey. Biology: Concepts and Connections, 6th edition. Benjamin Cummings Publishing. 2008.
Morgan’s fruit flies…
F2
Cambell, Reece, Taylor, Simon, and Dickey. Biology: Concepts and Connections, 6th edition. Benjamin Cummings Publishing. 2008.
Virtual Lab Simulation:
Drosophila Virtual lab – registration required (continue with
silde show for instructions.
Objective: Students will learn and
apply the principles of Mendelian
inheritance by experimentation with
the fruit fly Drosophila melanogaster.
Students will make hypotheses for
monohybrid, dihybrid and sex-linked
traits and test their hypotheses by
selecting fruit flies with different
visible mutations, mating them, and
analyzing the phenotypic ratios of the
offspring. Students will record their
observations into an online notebook
and write a lab report.
Drosophila Simulation:
Patterns of Heredity
Last slide (read instructions
first!)
Click on the Drosophila Link
for Registration
1. Create a new account
2. Class code (see last slide)
3. Enter your first and last
name (your username will be
generated for you)
4. Choose a password ' Write
down your user name and
passwords!
Website:
The top tab contains a
"notebook" link where you
can enter data gathered
during your experiments.
Also in the notebook tab,
you will write your report. All
notebook data and report
data will be saved and sent
to your teacher upon
completion.
Website’s
Notebook:
1. Start by ordering two wild type flies and
mate them.
2. View your flies under the microscope and
sort them.
3. View the flies close-up and note the
difference between males and females.
4. Add your data to your notebook.
5. Use the computer to "analyze results"
6. Go to the chi square analysis. Enter your
hypothesis. Since both of your parents with
wild type, you would expect a 50:50 ratio of
male to females. You will need to you a
calculator to determine the expected numbers
from the total number of offspring you have.
Enter that number in the "hypothesis" column.
7. The computer will do the chi square analysis
for you and show your statistical results.
8. Return to your notebook and look at your
data.
**Just play with the simulator for now to see what it does.
9. "Save" your notebook.
Understanding
the Program
Remove all your data from your notebook before you start
the real assignments.
For Assignment A (choose only one trait)
Apterous
Black Body
Brown Eyes
Curved Wings
1. Choose ONE trait from the autosomal
mutations on the table to study by ordering
flies of the mutant strain and crossing it with a
wild type fly.
2. Cross your flies (P generation) and determine
the phenotype of the F1 generation.
3. Now mate the offspring (F1) from that cross
together (creates F2 generation). Return to the
lab and choose "use fly in new mating" under
the microscope view.
4. Sort your F2 flies and analyze results. You can
choose to ignore sex here, since you know you
are studying only autosomal mutations. Show
that your results follow a 3:1 ratio.
5. Run a chi square analysis on your F2 flies
(again you can ignore sex).
Assignment A:
MONOHYBRID
CROSS
1. A reciprocal cross is a wild type
male x mutant female followed by a
mutant male x wild type female.
(Obviously, you study the same trait
here). Choose an allele found on the
sex chromosome. [See chromosome
map for sex linked alleles]
2. Show in your notebook how the
offspring differ depending on which
parent had the mutant phenotype. Be
prepared to explain why this happens
in your final lab report. You only need
to look at the F1 generation here.
Assignment B:
SEX-LINKED
TRAITS
1. Select any two traits on two
different chromosomes and study
their inheritance patterns
(DIHYBRID CROSS) [See
chromosome map] . Also be sure
that you do not pick any traits
that are LETHAL as this will skew
your data.
(a) Cross an F1 offspring with another
F1 offspring to generate an F2
generation. This should
demonstrate a 9:3:3:1 Mendelian
ratio
(b) (b) Test the 9:3:3:1 ratio by using
a chi-square analysis.
Assignment C:
DIHYBRID
CROSS
Click: HERE
http://www.sciencecourseware.com/vcise/drosophila/
If you are having difficulty, try this
virtual lab:
LabBench Activity: Genetics of Organisms
email your results