1. Ch14_Nov_23_s - 11/23/09


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Unformatted text preview: 11/23/09
 Muta-ons
in
a
gene’s
coding
sequence:
effects
on
expression
 41
 Muta-ons
outside
the
coding
sequence:
effects
on
expression
 42
 1
 11/23/09
 Chromosomal
Rearrangements
 • Ch
14
p489‐491;494‐503
 43
 Classify
muta-ons
–
effect
on
DNA
 44
 2
 11/23/09
 Subs-tu-ons
 e.g.,
CT
transi-on
 e.g.,
CA
transversion
 45
 Dele-ons
(Del)
 • Reversions
are
rare
if
more
than
a
few
nucleo-des
 •WHY?
   46
 3
 11/23/09
 Dele-ons
 • How
to
id
small
dele-ons?
 • How
to
id
large
dele-ons?
 47
 Dele-ons
 • Homozygosity
for
dele-on

o[en
lethal
 • Rare
cases

survive
 • Heterozygosity

may
survive
if
not
too
large
 • E.g.,

cri
du
chat
syndrome

del
on
5p
 • Why
isn’t
1
WT
copy
enough
in
dele-on
heterozygotes?
 • GENE
DOSAGE
 • Amount
of
gene’s
protein
product
rela-ve
other
 proteins
 • Precise
ra-os
may
be
needed
 48
 4
 11/23/09
 Dele-ons
&
Mapping
 • In
dele-on
heterozygotes,
dele-ons
may
reveal
recessive
muta-ons
 on
a
homologue 
 

 
 
=
PSEUDODOMINANCE
 51
 Dele-ons
&
Mapping
 What are polytene chromosomes? 53
 5
 11/23/09
 Polytene
Chromosomes
&
Mapping
 Each polytene arm is composed of hundreds of chromosomes aligned side by side. Repeated chromosome replication produces polytene chromosomes. 55
 Mapping
with
Dele-ons
 123456 1 - -++ - + 6
 11/23/09
 Duplica-ons
(Dp)
 • Increase
#
copies
of
a
chromosomal
region
 • Nontandem
vs.
tandem
 Hz
–
bulge
in
Dp
bearing
 chromosome
 58
 Polytene
Chromosomes…
 Bar eyes caused by duplication can be visualized on polytene chromosomes. 62
 7
 11/23/09
 Duplica-ons
&
Dele-ons
–
Evolu-onary
Outcome
 • Changes
in
gene
dosage

can
be
addi-ve
 • Large
dele-ons
or
duplica-ons

reduce
survival
 • Can
place
gene
in
new
loca-on

affects
expression
 • E.g.,
nearby
regulatory
elements
increase/decrease
 transcrip-on
of
gene
 • Alter
genome

drive
evolu-on
 • Remove
genes/add
genes
 • E.g.,
families
of
tandemly
repeated
genes
(hemoglobi)
 63
 Chromosomal
Muta-ons
&
Evolu-on
 8
 11/23/09
 Inversion
(Inv)
 65
 Origins
of
Inversions
–
Chromosome
Breakage
 66
 9
 11/23/09
 Consequences
of
Inversions
 • Inversions reorganize DNA sequence within a chromosome • Can have an intragenic break • Could have scenario where acts as recessive lethal mutation… 68
 Heterochroma-n

 Maison & Almouzni (2004) 71
 10
 11/23/09
 Consequences
of
Inversions
 • Inversions in heterozygotes (In/+)can suppress recombination 73
 Consequences
of
Inversions
 74
 11
 11/23/09
 Reciprocal
Transloca-on
 75
 Reciprocal
Transloca-on
 76
 12
 11/23/09
 Reciprocal
Transloca-on:
disease
 77
 Reciprocal
Transloca-on:
Alignment
&
Segrega-on
 • Segrega-on
in
transloca-on
homozygote
 • Chromosome
pairing
in
a
 transloca-on
heterozygote
 78
 13
 11/23/09
 Reciprocal
Transloca-on:
Alignment
&
Segrega-on
 • Chromosome
pairing
in
a
 transloca-on
heterozygote
 • Segrega-on
in
 transloca-on
 heterozygote
 79
 14
 ...
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