2.Ch14_Nov_23-27_slides_not_posted_earlier

2.Ch14_Nov_23-27_slides_not_posted_earlier - 11/29/09


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Unformatted text preview: 11/29/09
 Study
Chromosomal
Changes
via
Cytology
 45
 Dele>ons
 • Remember
re>noblastoma
&
Knudson’s
2‐hit
hypothesis?
 http://www.cancer.gov/cancertopics/understandingcancer/ cancergenomics/Slide53 50
 1
 11/29/09
 Dele>ons
 51
 Dele>ons,
Recombina>on
&
Mapping
 • What
happens
when
homologues
align
in
meiosis
in
a
dele>on
 heterozygote?
 • Progeny
of
dele>on
heterozygote
(del/+)
that
inherit
the
nondeleted
 homologue
(WT)
will
always
inherit
the
parental
allele
combina>on
 • WHY?
Because
no
recombina>on
in
that
area!
 53
 2
 11/29/09
 • Studying
chromosomal
changes:
 • Karyotyping,
compara>ve
gene
mapping
 • Exploit
unique
features
of
model
organisms
 • E.g.,
polytene
chromosomes
 Polytene
Chromosomes:
the
greatest
thing
since
 sliced
bread?
 Repeated chromosome replication produces polytene chromosomes. Each polytene arm is composed of hundreds of chromosomes aligned side by side. 55
 Phenotypic
Effects
of
Duplica>ons
 60
 3
 11/29/09
 Phenotypic
Effects
of
Duplica>ons
 • Some
duplica>ons
can
affect
survival
 • E.g.,

Triplolethal
locus
(Tpl+)
 61
 Duplica>ons
&
Unequal
Crossing
Over
 • Can generate gametes differ in gene copy # 62
 4
 11/29/09
 Polytene
Chromosomes…
 Bar eyes caused by duplication can be visualized on polytene chromosomes. 63
 Consequences
of
Inversions
 • Inversions reorganize DNA sequence within a chromosome Antennapedia gene example of a homeotic mutation 70
 5
 11/29/09
 Consequences
of
Inversions:
Proximity
to
 Heterochroma>n
 • Inversions
can
cause
inac>va>on
of
genes
via
spreading
of
heterochroma>n
 • Euchroma>n
–
lightly
staining
regions
of
chromosomes
 • Contains
most
genes
 • Heterochroma>n
–
darker
staining
regions
of
chromosomes
 • Highly
compacted
–
even
during
interphase
 • Typically
near
regions
in
centromere
 • Cons>tu>ve
heterochroma>n

regions
that
remain
condensed
most
 of
>me
in
all
cells
 • E.g.,
Y
chromosome
in
Drosophila
&
humans
 71
 Consequences
of
Inversions:
Proximity
to
 Heterochroma>n
 • Position-effect variegation – phenotypic effect of facultative heterochromatin Fig. 13.13 – Section 13.4 p479-481 (Heterochromatin & Position effect variegation) 73
 6
 11/29/09
 In
which
of
the
following
would
you
find
genes
that
are
turned
 on
in
certain
>ssues
and
turned
off
in
others?
 1.  2.  3.  4.  Cons>tu>ve
heterochroma>n
 Cons>tu>ve
euchroma>n
 Faculta>ve
heterochroma>n
 Euchroma>n
 • 
In
general,
which
of
the
following
chromosomal
muta>ons
has
a
 greater
chance
of
lethality
than
the
others?
 1.  2.  3.  4.  5.  Inversion
 Duplica>on
 Dele>on
 Transloca>on
 All
have
an
equal
chance
of
causing
lethality.
 7
 ...
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