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Mutations & Genetic
Recombination
Mutation
• Permanent change in the genetic material of an
organism
• All mutations in gametes are inheritable because they
are copied during DNA replication
• Somatic cell mutations occur in body cells
• Germ cell mutations occur in reproductive cells
• These are passed on from one generation to the next
Types of mutations
Point mutations
• Chemical change that affects just one
or a few nucleotides
• May involve substitution of one
nucleotide for another
• Or the insertion or deletion of one
or more nucleotides
Point mutations
• Minor effect on cell
• Change in coding sequence
does not always result in a
different polypeptide
• Ex. GGA  GGG both code
for the amino acid, glycine
• Even if the aa is substituted for another, it may not
have a significant function in the final structure
• This is called a silent mutation
• Example: UAU and UAC
• Mis-sense mutation
• Results in an altered protein
• Ex sickle cell disease is a point mutation that is very
harmful
Nonsense mutation
• Deletes a start signal or results in a premature stop
signal
• A nucleotide substitution that affects the regulatory
sequence may result in a cell being unable to produce
a functional protein
Frameshift
• When an insertion or a deletion
the codon reading frame is
shifted and each codon is read
incorrectly.
• AAU GGU GCC
• AAU GGUG GCC
Chromosomal Mutations
• Crossing over
• Loss or duplication of portions of DNA during DNA
replication
• Change to structural or regulatory DNA sequences
Causes of mutations
• Spontaneous mutations
• Caused by naturally
occurring molecular
interactions
• Ex. Incorrect base pairing
• Induced
• Caused by agents outside
the cell
• Mutagens increase the rate
of mutation
Physical Mutagens
• Cause physical changes to the
structure of DNA
• Ex. X-rays and gamma rays are the
most damaging form of mutagen
known
• Also UV rays cause chemical
reactions to form between
adjacent A and T bases, interfering
with replication
• A single sunburn doubles the
chance of getting skin cancer
(melanoma)
Chemical Mutagens
• A molecule that can enter the nucleus of the cell and
induce mutations by reacting chemically with DNA
• Can insert themselves and cause substitution or a
frameshift mutation
• Ex. Nitrates (a food preservative), gasoline fumes, 50
different compounds of cigarette smoke.
• Carcinogenic
• Chemical mutagens associated with one or more forms of
cancer
• Cancer is uncontrolled cell division
• The result of somatic cells that disrupt the expression of
genes involved in regulation of the cell cycle
Mutations and Genetic Variation
• Single mutation has little or no effect on an organism
• However, a series of mutations developed over time
can be more serious.
• Mutations accumulate within a cell
• Different mutations over time help shed light on
genetic variation
Tracing ancestry through mitochondrial DNA
• Mitochondria and chloroplasts have there own DNA (which
replicates, transcribes, and translates separately from nucleic DNA.
• Evidence suggests that these organelles were once independent
prokaryotic cells
• Endosymbiont theory proposes that eukaryotes arose when one
prokaryote was engulfed by another
Mitochodrial DNA (mtDNA)
• Recall, the cytoplasm of the fertilized egg (zygote) is donated by the ovum.
• All of your mtDNA is identical to your mothers
• Mutations in mtDNA provide information about the evolutionary path of
animals and plant species
The process of creating recombinant DNA involves 2 types of enzymes:
1. Restriction Enzymes – (DNA scissors) cut the DNA
strand at specific sites -palindromes- and often
creates sticky ends
2. The now unpaired segments can be paired with
complimentary nucleotides from a different strand
of DNA
3. DNA ligase – is genetic glue that puts DNA strands
back together.
•
rDNA
Application
• Insulin used to be harvested from pigs, but some
individuals did not tolerate it.
• we are now able to use bacteria to produce human
insulin in large quantities.
• is tolerated much better by patients.
• This procedure was first marketed in Canada in 1983!
Other Aspects of Biotechnology
• Gene sequencing –determining the specific location
and composition of specific genes.
• The Human Genome Project -1990 2000: mapped
our 30 000 genes (3 billion nucleotides)
• NOVA Online | Cracking the Code of Life | Sequence
for Yourself
• RFLP – restriction fragment length
polymorphism –cut DNA into pieces
• Gel Electrophoresis – separate the DNA
pieces by size.
• DNA fingerprinting
• identify an individual based on their unique
genetic code.
• homologous segments of DNA are similar
but contain unique patterns of nitrogen
bases
• identify individuals involved in crimes,
paternity
DNA Fingerprinting
Misc. Technology
• Polymerase chain reaction –making billions of copies of a piece of
DNA- PCR Animation
• Paternity Testing - Paternity Testing
• Gene Gun - Genegun1
Recombinant DNA
• Genetic engineering
• Manipulating genetic material to alter genes and blend
plant, animal, and bacteria DNA together.
• DNA that includes outside source is called
recombinant DNA.
• Rapidly growing field
• Eg peppers
Restriction Endonucleases
• Restriction enzymes cut DNA at specific nucleotide sequences
• Restriction endonucleases cuts within the interior of a DNA molecule
(rather than at ends)
• It recognizes a target sequence (short sequence of nucleotides) and
cuts within it at the restriction site.
• Two characteristics
• Specificity: cuts are specific and predictable
• Meaning the same enzyme will cut the same target
sequences producing the same set of DNA fragments called
restriction fragments
• Staggered cuts:
• leave a few unpaired nucleotides on a single strand at each
restriction fragment called sticky ends.
• Sticky ends can pair with a complementary sticky end
cut by he same restriction endonuclease from a
different strand of DNA
• DNA ligase Spliced the paired sticky ends together
resulting in a stable recombinant DNA molecule.
animation