8. Lab 4 Answer Key (all labs)

8. Lab 4 Answer Key (all labs) - All days:

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Unformatted text preview: All days: 3.
(9
marks)
R.
K.
Sakai,
K.
Akhtar,
&
C.J.
Dubash
(1985,
J
Hered
76:140‐141)
reported
data
from
a
set
of
 testcrosses
with
the
mosquito
Anopheles
culicifacies,
a
vector
for
malaria
in
souther
Asia.
The
data
involved
three
 mutations:
bw
(brown),
c
(colourless
eyes),
and
Blk
(black
body).

In
each
cross,
trans
heterozygotes
were
mated
 to
the
mosquitoes
homozygous
for
the
recessive
alleles
of
the
genes,
&
the
progeny
were
scored
as
having
either
 a
parental
or
a
recombinant
genotype.

Are
any
of
the
three
genes
studied
in
these
crosses
linked?

If
so,
 construct
a
map
of
the
linkage
relationships.
 Cross
 1
 2
 3
 
 Trans
 Heterozygote
 bw
+/+
c
 bw
+/
+
Blk
 Blk
+/
+
c
 Parental
 850
 750
 629
 Progeny
 Recombinant
 503
 237
 183
 
 %
 Recombination
 37.2
 24
 22.5
 2
marks
each
for
calculation
of
recombination
frequencies

‐
1
for
showing
calculation
itself;
1
for
final
 answer.
 In
each
cross,
the
frequency
of
recombination
is
less
than
50%,
so
all
3
loci
are
linked.

 3
marks
for
genetic
map
 
 
 
 bw
‐‐‐‐24.0‐‐‐‐‐Blk‐‐‐‐22.5‐‐‐‐c 
 
 
 
 I‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐37.2‐‐‐‐‐‐‐‐‐‐‐‐‐I
 
 Notice
the
recombination
frequency
between
bw
and
c
is
substantially
less
than
the
actual
distance
b/w
these
 genes.

This
shows
that
for
widely
separated
genes,
the
recombination
frequency
underestimates
the
true
map
 distance.
 7 All days: (You may have different gene names.) 4.
(2
marks)
(Mon
&
Thurs)
An
individual
homozygous
for
CDE
is
mated
to
one
homozygous
for
cde.
From
a
 testcross
between
the
F1
individuals
1000
offspring
are
produced.
The
class
that
was
C‐D‐ee
included
351
 individuals.
Are
the
genes
C,
D,
and
E
on
the
same
or
different
chromosomes?

Explain.


 OR

 (2
marks)
(Tues
&
Wed)
An
individual
homozygous
for
JKL
is
mated
to
one
homozygous
for
jkl.
From
a
testcross
 between
the
F1
individuals
1000
offspring
are
produced.
The
class
that
was
J‐kk‐L‐
included
360
individuals.
Are
 the
genes
J,
K,
and
L
on
the
same
or
different
chromosomes?

Explain.


 The
class
represented
by
351
or
360
offspring
indicates
that
at
least
two
of
the
three
genes
are
linked
because
 they
are
still
in
their
parental
allelic
combination
(2
marks
for
an
explanation
similar
to
this).
C
&
D
appear
 linked;
J
&
L
appear
linked.
(1
bonus
mark
if
they
tell
you
which
genes
appear
to
be
linked.)
 
 
5.
(2
marks)
If
a
is
linked
to
b
and
b
to
c,
and
c
to
d,
does
it
follow
that
a
recombination
experiment
would
detect
 linkage
between
a
and
d?
Explain.
 No.
The
genes
a
and
d
could
be
very
far
apart
on
the
same
chromosome—so
far
apart
that
they
recombine
 freely,
that
is,
50
percent
of
the
time.
 (2
marks
for
an
explanation
similar
to
this.)
 
 
 
 6.
(7
marks)
(Mon
&
Thurs)
The
s
(starry)
and
t
(tiny)
genes
alter
the
appearance
of
butterfly
wings.
They
are
 linked
and
are
10
m.u.
apart.
True‐breeding
parents
SStt
and
ssTT
are
crossed
to
form
the
F1.
If
the
F1
is
test‐ crossed,
what
proportion
of
the
progeny
will
be
Sstt?
Diagram
the
cross
and
clearly
show
how
you
calculated
your
 answer.


 OR (7
marks)
(Tues
&
Wed)
The
s
(starry)
and
m
(miniature)
genes
alter
the
appearance
of
butterfly
wings.
They
are
 linked
and
are
10
m.u.
apart.
True‐breeding
parents
SSmm
and
ssMM
are
crossed
to
form
the
F1.
If
the
F1
is
test‐ crossed,
what
proportion
of
the
progeny
will
be
Ssmm?
Diagram
the
cross
and
clearly
show
how
you
calculated
 your
answer.


 St/St x sT/sT St/sT x st/st 
(4
marks
for
cross)
 Looking
for
progeny
with
St/st 
 
get
st
from
testcross
parent;
other
comes
from
heterozygous
F1
 parent
–
it
is
a
parental
configuration
of
alleles.
If
the
genes
are
10
m.u.
apart,
thus
there
is
10%
 recombination
b/w
them.
So
10%
of
the
time
will
get
recombinants;
90%
of
time
will
get
parentals.
(2
 marks
for
something
that
approaches
this
logic.)
 However,
we’re
only
looking
for
ONE
of
the
parental
homologues,
so
90%/2
=
45%
(1
mark
for
this.)
 45%
of
the
progeny
should
be
St/sT
 8 ...
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This note was uploaded on 01/10/2010 for the course BIOLOGY biol2040 taught by Professor Tamarakelly during the Fall '09 term at York University.

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