Mutations Genetic Recombination Mutation Permanent change in the
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 (mt. DNA) • Recall, the cytoplasm of the fertilized egg (zygote) is donated by the ovum. • All of your mt. DNA is identical to your mothers • Mutations in mt. DNA 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. • r. DNA
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 - Genegun 1
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.
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