Inheritance
Patterns
of
Drosophila
melanogaster,
the
Fruit
Fly
Kevin
Reynolds
School
of
Natural
Sciences
at
Ferrum
College
kreynolds@ferrum.edu
Abstract
This
lab
was
performed
to
further
our
understanding
of
the
basis
of
Mendelian
genetics.
We
did
this
by
crossing
fruit
flies
we
found
in
our
laboratory.
We
performed
four
crosses:
female
wild‐type
to
male
ebony
body,
female
white
eyes
to
male
wild‐type,
female
wild‐type
to
male
sepia
eyes/ebony
body,
and
female
ebony
body
to
male
vestigal
wings.
We
found
that
each
cross
showed
an
inheritance
pattern
of
either
a
standard
monohybrid
cross,
sex‐linked
monohybrid,
dihybrid
cross
of
unlinked
genes,
and
a
dihybrid
cross
of
linked
genes.
Introduction
The
purpose
of
this
lab
was
to
further
our
understanding
of
inheritance
patterns
and
to
get
hands
on
experience
with
Mendelian
genetics.
To
do
this
we
are
looking
at
the
inheritance
patterns
of
the
mutant
fruit
flies
we
discovered
in
our
laboratory.
We
want
to
look
at
the
phenotypic
characteristics
of
our
specimens
and
determine
the
patterns
for
how
each
trait
is
inherited.
Many
organisms
are
used
to
study
Mandelian
genetics
such
as
fruit
flies,
yeast,
E.
coli,
and
mice.
We
have
chosen
fruit
flies
to
focus
for
a
few
key
reasons;
because
fruit
flies
are
small,
cheap,
easy
to
keep
in
large
numbers,
and
have
a
short
life
cycle,
from
egg
to
adult
in
about
10
days
at
room
temperature,
they
are
idea
for
a
classroom
study.
In
this
procedure,
we
are
looking
for
four
distinct
inheritance
patterns,
standard
monohybrid
cross,
sex‐linked
monohybrid,
dihybrid
cross
of
unlinked
genes,
and
a
dihybrid
cross
of
linked
genes.
A
standard
monohybrid
cross
is
a
cross,
of
a
single
trait,
between
a
homozygous
dominant
and
a
homozygous
recessive
to
produce
a
heterozygous
F1
generation,
which
when
is
selfed
produces
an
expression
rate
of
three
1
dominant
to
one
recessive.
A
sex‐linked
monohybrid
cross
is
a
cross
where
the
trait
is
linked
to
the
X‐chromosome,
since
in
fruit
flies
a
male
is
denoted
by
lacking
a
second
X‐
chromosome.
In
both
make
and
female
you
would
see
roughly
equal
numbers
of
both
traits
expressed.
The
third
type
of
inheritance
pattern
we
could
have
is
a
dihybrid
cross
of
unlinked
genes.
This
is
a
cross
between
two
parents,
one
being
homozygous
dominant
for
both
genes
and
the
other
being
homozygous
recessive
for
both
genes.
When
we
examine
our
F1
generation
we
would
see
that
we
have
a
nine
to
three
to
three
to
one
ratio.
The
nine
offspring
would
look
like
the
parent
whom
was
dominant
for
both
genes
and
the
one
offspring
would
look
like
the
parent
whom
was
homozygous
recessive
for
both
genes.
The
final
possible
inheritance
pattern
we
could
observe
is
a
dihybrid
cross
of
linked
genes.
This
is
where
two
genes
are
generally
inherited
together.
However,
due
to
recombination
you
will
find
both
recombinant
offspring
and
parental
offspring.
How
much
recombination
depends
on
the
recombination
frequency,
how
often
crossing
over
occurs
between
genes,
which
is
how
far
apart
the
genes
are
on
the
chromosome.
In
the
F2
generation
we
would
see
a
deviation
from
a
nine
to
three
to
three
to
one
ratio,
where
both
parental
phenotypes
and
recombinant
phenotypes
are
present,
but
just
how
much
of
a
deviation
depends
on
the
recombination
frequency.
Methods
Examination
of
Flies:
To
look
at
the
flies
we
anesthetized
them
using
flynap,
which
is
composed
of
ethanol
and
triethylamine.
We
dipped
a
wand
into
the
flynap
and
put
that
into
the
tubes,
for
about
three
to
five
minutes,
of
flies
until
they
were
anesthetized,
being
careful
not
to
let
the
flies
escape
or
fall
into
the
food
at
the
bottom
of
the
tubes.
We
then
put
the
flies
on
an
index
card
to
look
at
them
under
a
dissecting
microscope
at
10X
to
25X
magnification.
To
move
the
flies
around
we
used
a
small
paintbrush.
We
looked
to
see
if
the
fly
was
a
male
or
female.
This
was
achieved
by
looking
at
the
size(females
are
usually
larger),
shape(the
males
abdomen
is
narrow
where
the
female
is
spherical),
color(the
male
has
a
large
black
dot
on
his
abdomen),
and
external
genitalia(males
have
a
darkly
colored
external
genitalia
on
the
ventral
side
of
the
abdomen).
We
also
looked
at
distinguishable
characteristics
so
we
could
separate
the
different
flies
that
were
needed
for
each
cross.
Mating
Setup:
To
set
up
the
crosses,
we
put
a
scoop
of
dry
food
and
a
scoop
of
water
into
each
tube;
one
tube
was
used
for
each
parent
cross,
and
four
parent
crosses
were
done.
We
placed
about
three
virgin
females
into
each
tube
for
every
one
male.
We
ended
up
with
roughly
ten
females
and
three
males
in
each
tube
per
cross.
The
tubes
were
then
put
in
an
incubator
at
25°C.
Crosses
Performed:
We
performed
four
crosses.
Our
first
cross
was
a
monohybrid
cross
of
female
wild‐
type
to
male
ebony
body.
Our
second
cross
was
another
monohybrid
cross
of
female
white
eyes
to
male
wild‐type.
The
third
cross
was
a
dihybrid
cross
of
female
wild‐type
to
male
ebony
body/sepia
eyes.
The
final
cross
we
performed
was
female
ebony
body
to
male
vestigal
wings.
Analysis
of
F1
and
F2:
It
takes
approximately
ten
days
for
flies
to
develop
from
an
egg
to
an
adult
at
25°C,
so
after
about
two
weeks
we
look
at
what
the
parental
cross
had
produced,
which
are
the
F1
generation.
We
looked
at
them
and
transferred
them
to
a
separate
tube
for
each
cross.
We
then
let
the
F1
generation
from
each
tube
self
cross.
After
another
two
weeks,
when
the
F1
offspring
had
matured,
we
counted
and
looked
at
our
F2
generation.
When
we
looked
at
the
flies,
we
examined
to
see
what
phenotype
they
were
and
to
see
if
they
were
male
or
female.
For
the
F1
and
F2
generation
we
counted
one
hundred
flies.
We
counted
just
as
we
had
done
with
the
parents.
We
a
anesthetized
them
with
flynap
and
examined
them
under
a
dissecting
microscope.
Results
2
Four
flies
of
the
five
we
crossed
had
different
and
distinct
characteristics
from
the
others.
Wild
type
flies
have
a
light
brown
body,
red
eyes,
and
long
oval
wings.
White
eyed
flies
have
a
light
brown
body,
white
eyes,
and
long
oval
wings.
Ebony
body
flies
have
an
ebony
body,
red
eyes,
and
long
oval
wings.
The
vestigal
flies
have
a
light
brown
body,
with
re
eyes,
and
tiny
wings.
The
final
fly
type,
ebony/sepia,
have
black
bodies,
brown
eyes,
and
long
oval
wings.
F1
Phenotypes
and
Counts:
Table
1.1
shows
the
offspring
from
athe
cross
between
female
wild‐type
and
male
ebony
body(cross
1).
Table
1.1
Phenotype
#
of
Females
#
of
Males
Wild‐type
43
57
Table
1.2
shows
the
offspring
from
teh
cross
between
female
white
eyes
to
male
wild‐type(cross
2).
Table
1.2
Phenotype
#
of
Females
#
of
Males
White
eyes
0
47
Wild‐type
53
0
Table
1.3
shows
the
offspring
from
the
cross
between
female
wild‐type
and
male
ebony
body/sepia
eyes(cross
3).
Table
1.3
Phenotype
#
of
Females
#
of
Males
Wild‐type
43
57
Table
1.4
shows
the
offspring
from
the
cross
between
female
ebony
body
and
male
vestigal
wings(cross
4).
Table
1.4
Phenotype
#
of
Females
#
of
Males
Wild‐type
58
42
F2
Phenotypes
and
Counts:
Table
2.1
shows
the
offspring
when
the
F1
generation,
from
the
first
cross,
was
allowed
to
self‐mate
with
each
other.
Table
2.1
Phenotypes
#
of
Females
#
of
Males
Wild‐Type
36
41
Ebony
Body
15
8
Table
2.2
shows
the
offspring
when
the
F1
generation,
from
the
second
cross,
was
allowed
to
self‐mate
with
each
other.
Table
2.2
Phenotypes
#
of
Females
3
of
Males
White
eye
19
22
Wild‐type
36
23
Table
2.3
shows
the
offspring
when
the
F1
generation,
from
the
third
cross,
was
allowed
to
self‐mate
with
each
other.
Table
2.3
Phenotype
#
of
Females
#
of
Males
Wild‐type
14
45
Ebony
body
7
10
Sepia
eyes
14
1
Ebony/Sepia
5
4
Table
2.4
shows
the
offspring
when
the
F1
generation,
from
the
fourth
cross,
was
allowed
to
self‐mate
with
each
other.
Table
2.4
Phenotype
#
of
Females
#
of
Males
Wild‐type
38
26
Ebony
body
16
10
Vestigal
wings
7
1
Ebony/Vestigal
0
2
Conclusions
Analysis
of
F1
Generation
Data:
Because
all
of
our
parent
crosses
were
either
a
homozygous
monohybrid
or
a
homozygous
dihybrid,
one
parent
being
dominant
and
the
other
recessive,
we
can
determine
which
traits
were
dominant
and
which
traits
were
recessive.
In
the
first
cross
between
female
wild‐type
and
male
ebony
body
all
of
the
F1
generation
were
wild‐type,
therefore
wild‐type
is
dominant.
The
cross
between
female
white
eyes
and
male
wild‐type
produced
all
female
wild‐
type
and
all
white
eye
males.
Since
the
parental
male
wild‐type
gives
his
only
X‐
chromosome
to
his
daughters,
and
all
of
his
daughters
express
wild‐type,
we
can
say
that
3
wild‐type
is
dominant
and
white
eyes
is
recessive.
In
the
cross
between
female
wild‐
type
and
ebony
body/sepia
eyes,
all
of
the
F1
generation
was
wild‐type.
Therefore,
we
can
say
that
wild‐type
is
dominant
to
ebony
body/sepia
eyes.
Finally,
since
the
cross
between
female
ebony
body
and
vestigal
wings
yielded
all
wild‐type
F1
generations,
we
can
determine
wild‐type
is
dominant
to
both
vestigal
wings
and
ebony
body,
and
that
vestigal
wings
and
ebony
body
are
linked
genes.
Analysis
of
F2
Generation
Data:
With
a
first
look
at
the
data
it
is
my
hypothesis
that
the
cross
between
female
wild‐type
and
male
ebony
body
will
be
a
standard
monohybrid
cross.
I
also
hypothesis
that
the
female
white
eyes
and
male
wild‐type
is
a
sex‐linked
monohybrid
cross.
The
female
wild‐type
crossed
with
male
ebony
body/
sepia
eyes
will
most
likely
be
a
dihybrid
cross
of
unlinked
genes.
Therefore,
the
cross
between
female
ebony
body
and
male
vestigal
wings
must
be
a
dihybrid
cross
of
linked
genes.
However,
we
cannot
be
certain
until
a
Chi‐Squared
Test
is
performed.
Chi‐Squared
Test:
Table
3.1
shows
the
Chi‐Squared
test
on
the
cross
of
female
wild‐type
and
male
ebony
body.
Table
3.1
Traits
Observed
Expected
(O‐E)2/E
Wild‐
77
75
0.053
type
Ebony
23
25
0.16
body
dF=
1
Σ2=0.213
P
range=
0.750‐0.500
After
performing
the
Chi‐Squared
test
we
determined
or
P
range
to
be
between
0.750
and
0.500,
therefore
we
can
say
that
any
discrepancies
in
our
data
is
caused
by
random
chance.
So
the
hypothesis
holds
correct
that
this
cross
is
a
standard
monohybrid
cross.
Table
3.2
shows
the
Chi‐Squared
test
on
the
cross
of
female
white
eyes
and
male
wild‐type.
Table
3.2
Traits
Observed
Expected
(O‐E)2/E
Wild‐
59
50
1.62
type
White
41
50
1.62
eyes
dF=
1
Σ2=
3.24
Table
3.4
Traits
Wild‐
type
Ebony
body
Vestigal
wings
Ebony/
Vestigal
dF=
3
P
range=
0.100
to
0.050
P
range=
greater
than
0.050
Since
we
did
not
perform
at
test
cross
with
the
F1
Generation,
we
cannot
prove
that
this
is
a
dihybrid
cross
of
linked
genes.
However,
we
can
prove
that
it
is
not
a
standard
dihybrid
cross
of
unlinked
genes.
Since
our
P
range
is
grater
than
0.050,
the
cross
fails
the
Chi‐Squared
test
thereby
proving
that
the
cross
cannot
be
a
standard
dihybrid
cross.
If
a
test
cross
had
been
performed
it
is
probable
that
parental
types
would
have
been
the
most
abundant
in
the
F2
Generation
and
there
would
have
been
a
small
percentage
of
recombinant
phenotypes
present
in
the
results
from
the
test
cross.
References
1. Hartwell,
Leland
H.
Hood,
Leroy.
Goldberg,
Michael
L.
Reynolds,
Ann
E.
Silver,
Lee
M.
Verus,
Ruth
C.
GENETICS:
From
Genes
to
Genomes‐
Third
Edition.
New
York:
The
McGraw
Hill
Companies,
Inc.,
2008
2. Mertens
and
Hammersmith.
“BIO
305
Introduction
to
Genetics
Laboratory
Manual”.
Ferrum
College.
2007
3. “FLYNAP”.
2010
July
13.
<http://www.carolina.com/text/teac
herresources/MSDS/flynap.pdf>
Acknowledgments
Again
we
see
that
because
our
P
range
is
between
0.100
and
0.050,
our
hypothesis
is
proven
valid,
and
the
data
statistically
matches
the
inheritance
pattern
of
a
sex‐linked
monohybrid
cross.
Table
3.3
shows
the
Chi‐Squared
test
on
the
cross
of
female
wild
‐type
and
male
ebony
body/sepia
eyes.
Table
3.3
Traits
Observed
Expected
(O‐E)2/E
Wild‐
59
56
0.161
type
Ebony
17
19
0.211
body
Sepia
15
19
0.842
eyes
Ebony/
9
6
1.5
Sepia
dF=
3
Σ2=
2.714
P
range=
0.500
to
0.250
Here
the
hypothesis
also
holds
up,
showing
that
the
cross
is
a
standard
dihybrid
cross.
Table
3.4
shows
the
Chi‐Squared
test
on
the
cross
of
female
ebony
body
and
male
vestigal
wing.
4
Observed
Expected
64
56
(O‐E)2/E
1.143
26
19
2.259
8
19
6.368
2
6
2.667
Σ2=
8.473
I
would
like
to
thank
Josh
Liptak,
John
Harper,
Ross
Beckner,
and
Jessica
Foley
for
their
assistance
with
this
lab.
I
would
also
like
to
thank
Dr.
Gazdik
for
her
guidance
throughout
the
entire
lab.
5