2. Drosophila Melanogasteris used to study the biological
processes underlying:
• Embryonic development
• Neurodegenerative disorders
• Diabetes
• Aging
• Drug abuse
• Cancer
• Behavior
• Evolution
3. Characteristics of Drosophila that make it a good
model organism
• Small, easy and cheap to maintain and manipulate
• Allows easy observation
• Rapid development
• Short lifespan
• Produce large numbers of offspring
• Availability of mutants
• Development is external → Manipulation at most developmental
stages
• Lots of previous experiments and discoveries
• Genome is sequenced
• Homologues for at least 75 % of human disease genes
• Fewer ethical concerns
4. Life cycle of Drosophila
• The female fruit fly (3mm in length), will lay
between 750 and 1500 eggs in her life time
• The life cycle is about 10 - 12 days at room
temperature (25oC)
• After the egg (at a mere half a milimeter in length)
is fertilized, the embryos emerges in 24 hours
• The embryo undergoes successive molts to
become the first, second, and third instar larva
• The larval stages is characterized by consumption
of food and resulting growth, followed by the
pupal stage, during which metamorphosis
followed by the emergence of the adult fly
5. Identify the different stages of Drosophila development
• The egg: Eggs are small, oval shaped, and
have two filaments at one end.
•The larval stage: The larva look like worms.
They use black mouth hooks to eat. Three
larval stages.
• The pupal stage: A pupa undergoes four
days of metamorphosis. They form a hard and
dark pupal case.
• The adult stage: Adult flies have a head,
thorax, abdomen, six legs, and two wings.
They live a month or more and then die. A
female does not mate for 10-12 hours after
emerging from the pupa.
Under standard laboratory conditions (25°C
temperature and 70% humidity) the whole
life cycle does not take longer than ~ 10 days
6. Identify males versus
females
1. Size of adult The female is larger
than the male.
2. Shape of abdomen The female
abdomen curves to a point; the male
abdomen is round
3. Markings on the abdomen
Alternating dark and light bands can
be seen on the entire rear portion of
the female; the last few segments of
the male are fused.
4. Appearance of sex comb On males
there is a tiny tuft of hairs on the
front legs.
sex comb
7. The differences between
the sexes
Male Female
Size Small Large
Shape of abdomen Black and round
Transparent and
pointed posterior
Markings on the
abdomen
5 abdominal
segments
7 abdominal
segments
Sex combs tiny tuft of hairs on
the front legs
Absent
8. Drosophila Genome
• Drosophila has four pairs of chromosomes:
– the X/Y sex chromosomes (a pair of sex
chromosomes (two X chromosomes for
females, one X and one Y for males),
– the autosomes 2,3, and 4.
• The fourth chromosome is quite tiny and
the smallest one.
• The genome was (almost) completely
sequenced in 2000, analysis of the data is
now mostly completed.
9. 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.
Terminology
Drosophila wild-type Drosophila mutant: white eye
11. Mutant phenotypes
Altered wing structures
• Vestigal-winged flies, vg
• Curly-winged flies, Cy
• Dichaete, D
• Cut wings, Xct
Abnormally body color
• Ebony body,e
Colored eyes
• White eyes flies, Xw
• Bar eyes flies, B
Strangely formed heads
• Eyeless flies, ey
• Leg-headed flies
Vestigal
wings
Curly
wings
Cut
wings
Dichaete
Ebony Body
White eyes Bar eyes
Eyeless Leg-headed flies
12. Bar eyes, B Cut wing, ct
Vestigal wings, vg Curly wings, Cy Dichaete, D
X X
II II III
13. Mutant phenotypes
Altered wing structures
• Vestigal-winged flies, vg ;
– crumpled wings (short wings) that prevent them from being
able to fly properly
– have defect in the ‘vestigal gene’ which is on the second
chromosome
– an autosomalrecessive trait
• Curly-winged flies, Cy;
– defect in the ‘curly gene’ which is on the second chromosome
– An autoomaldominanttrait
• Dichaete, D;
– defect in the Dichaete gene which is on the third chromosome
– a dominantmutation
• Cut wings, Xct
– defect in the gene located on the X chromosome
Vestigal
wings
Curly
wings
Cut
wings
Dichaete
14. Mutant phenotypes
Abnormally body color
• Ebony body, e;
– a dark, almost black, body
– they carry a defect in their "ebony gene," on the third
chromosome
– normally, the ebony gene is responsible for building up
the tan-colored pigments in the normal fruit fly
– if the ebony gene is defective, the black pigments
accumulate all over the body
– an autosomal recessive trait
Ebony Body
15. Colored eyes
• White eyes flies, Xw;
-have white eyes.
-have completely a defect in their "white"
gene
-these mutant types produce no red pigment
at all
-mutation on the X chromosome
• Bar eyes flies, B;
-have round, thin and slit-like eyes
-the eye of the fly is normally an elongated
oval shape whereas the bar eye phenotype is
much thinner.
-they carry a duplication in region of 16A
(ebony gene) of the X chromosome
Mutant phenotypes
White eyes
Bar eyes
16. Strangely formed heads
• Eyeless flies, ey;
-no eyes
-defect in their "eyes absent" gene
• Leg-headed flies;
-abnormal, leg-like antennas on their
foreheads
-have a defect in their (antennapedia) gene
which normally instructs some body cells to
become legs
Mutant phenotypes
