Drosophila
Why Fruit Flies?
• Fruit Flies (Drosophila melanogaster) have been
used to study genetics for the past 90 years.
• Why?
• 50% of their genes are the same as humans
• Complex genetic systems (similar to ours)
• Short life cycle
• Reliable reproducers
• Several mutations which can be used to study the
inheritance of mutated genes.
How do we observe fruit flies?
They are very small so we need to use a
microscope:
But we need to put them to sleep first:
The Fly nap will
keep the flies
Anaesthetised for
Approximately
45 minutes
Breeding Fruit Flies
In order to breed fruit flies, we need to be able to tell which sex
they are.
Male
Female
Which one’s which?
Setting up a breeding tube:
1. Add food medium to the tube and moisten
2. Add a ‘ladder’ or other matrix for the flies to climb (and
breed) on.
3. Insert a foam bung to seal the tube but still allow air in/out.
• http://www.youtube.com/watch?v=zXXqQ2zJ
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Drosophila Life Cycle
Larva:
Pupa:
• http://www.youtube.com/watch?v=DkiCFkB9c
So
Wild type Drosophila
A ‘normal’ (not mutated) drosophila fly is
referred to as a ‘’Wildtype’’ and has the
following traits:
Non-Ebony
(Brown) body
Normal
Length wings
Red Eyes
Drosophila Mutations
1. Ebony Body
These Flies have a much darker
(almost black) body.
When writing the Genotype,
We denote it as Eb
The normal ‘wildtype’
version is written Eb+
2. Vestigial Wings
Some Drosophila have the gene
mutation which means the wings
don’t form properly (vestigial)
When writing the
genotype, we denote
it as Vg
(or Vg+)
3. White Eyes
Some flies have a mutation
which causes their eyes to
be white instead of red.
This mutation is carried on the
X chromosome so
The mode of inheritance called
X-Linked or
Sex-Linked
• http://www.youtube.com/watch?v=UL4A0gKu
ZoI
VgEb Inheritance.
Vg = Vestigial Wings Vg+ = Non vestigial
Eb = Ebony body
Eb+ = Non ebony
For each genotype, write the phenotype.
Vgvgebeb vg+vg+eb+eb+ vgvg+ebeb
Vgvg+ebeb+ vgvgeb+eb+
Answers:
1) Vgvgebeb
Vestigial wings, ebony body
2) vg+vg+eb+eb+
Non-Vesitigal Non-Ebony
3) vgvg+ebeb
Non-vesitigial, Ebony body
4) Vgvg+ebeb+
Non-Vesitigial, Non-Ebony
5) vgvgeb+eb+
Vesitigial Wings, Non-Ebony body
Now try constructing a Punnett
square:
Using the template on the worksheet, and your
knowledge of dihybrid inheritance, fill in the
cross for the F1 and F2 generation.