Download Bio290-08-Week 9

Today’s Agenda:
1. A Microarray Primer
2. Guest Speaker:
Dr. Michael Schlador
3. Follow-up: the Use of
Microarray Analysis
in Chemotherapeutics
4. Preview of Chapter 15 &
16
Chapter 15: Mutations
• Mutations generate
genetic variants
• These variants are then
subject to
recombination
Consequences of mutations
What would you predict if the
mutations was…..
• Within a coding region
• Within a noncoding region
What are the effects of point
mutations on gene products?
Are mutations random or induced?
• Luria and Delbruck used
the “fluctuation test”
• They were interested in
determining which
hypothesis was correct
Replica plating
What can cause spontaneous
mutations?
• Errors in DNA
replication
– Transitions: base pairs
mismatch
– Transversions: base pair
mismatch with the
normal keto base forms
What can cause spontaneous
mutations?
• Errors in DNA
replication
– Frameshift mutations:
Also known as indel
mutations
Trinucleotide repeats may lead to
disease…why?
How can we induce mutations?
• Use base analogs
– Cause incorrect base
pairing
How can we induce mutations?
• Use intercalating agents
which mimic base pairs
and slip in between the
base pairs…promote
indel mutations
How can we induce mutations?
• Promote base damage
– UV light
– Ionizing radiation
• Promotes large strand
breaks
– Aflatoxin B1
• Binds to guanine and
generates an apurinic site
Ames Test is to determine mutagenicity
Biological Repair Mechanisms
• Direct reversal of
damaged DNA
• Base-excision repair
• Nucleotide-excision
repair
• Mismatch repair
Direct reversal of damaged DNA
Base-excision repair
• Carried out by DNA
glycolylases, generate
apurininc or apyrimidinic
sites
• AP endonuclease nicks
strand
• Deoxyribophosphodiesterase removes more
DNA
• DNA polymerase fills in the
gap with new DNA
Nucleotide-excision repair
• Used to repair base
damage or transcription
blocks
• Autosomal recessive
diseases, Xeroderma
pigmentosum and
Cockayne Syndrome
result from defects in
this system
Mismatch repair
• Recognize mismatch
base pairs
• Determine which base
is the incorrect one
• Excise the incorrect
base and repair DNA
Error prone repair
• Known as translesion
synthesis, requires a
bypass polymerase
Repair of double-strand breaks
• What conditions can cause double strand
breaks?
• There are two possible situations:
– Nonhomologous end joining
– Homologous recombination
Nonhomologous end joining
Homologous recombination
• Damage corrected by
synthesis-dependent
strand annealing (SDSA)
• Uses sister chromatids
as templates
Why can mutations lead to cancer?
• Two types of mutations associated with
cancer
– Oncogenes are activated
– Tumor suppressor genes are inactivated
Oncogenes
• Genes that control the
cell cycle or inhibit
apoptosis are
considered protooncogenes
Tumor Suppressor genes
• Often these genes participate in regulation of
cell cycle, activate cell apoptosis, or repair of
damaged DNA
• Mutations in p53 result in 50% of all tumors
Chapter 16: Changes in
chromosomes
Chromosome numbers
• Changes in
chromosome sets are
known as aberrant
euploidy
• Changes in parts of
chromosome sets is
known as aneuploidy
Polyploids
• More common in plants
• Correlation between the number of
chromosome sets and size of organism
• Autopolyploids: multiple chromosomes from
one species
• Allopolyploids: sets of chromosomes from two
or more different species
Agricultural applications
• Monoploid plants provide a way to select for
desired traits
Agricultural applications
• Bananas are sterile
triploids
• Autotetroploid grapes
are larger than diploid
grapes
Aneuploidy
• Mostly due to
nondisjunction during
meiosis or mitosis
Abnormal numbers of sex
chromosome
• Turner Syndrome
– Result of only one sex
chromosome (XO)
Abnormal numbers of sex
chromosome
• Klinefleter Syndrome
– The result of an extra X
chromosome (XXY)
Abnormal number of autosomes
• Down syndrome
– Results from an extra
copy of chromosome 21
Can Down syndrome be inherited?
Cancer from translocation
Readings for Chapter 15/16
• Chapter 15: all sections except 15.5
• Chapter 16: section 16.1, 16.2 Robertsonian
translocation (584-585) and rearrangements
and cancer (587)