Biol 121- 2010.03.03- Genetics- Gene Technology (Ch. 19).docx

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Biol 121 225
Freeman 390-395, 407-411, 417-424 Mar. 3, 10
Ch. 19, Gene Technology
Pituitary dwarfism and growth
-people with pituitary dwarfism have defective copies of the gene GH1 which
codes for the GH1 growth hormone protein
-affected people are typically no more than 4 feet tall by adulthood
-growth hormone was injected into people just like insulin injections for diabetes
-only growth hormone from humans worked, and therefore it had to be extracted
from cadavers (dead bodies) and therefore was scarce/expensive
-even worse, infectious proteins called prions that cause degenerative brain
disorders emerged in patients people can get prions by inheritance or by eating
prion proteins
-their growth hormone supply was contaminated with a prion protein from the
brains of the cadavers supplying the hormone
-retroviruses are currently the vector of choice in gene therapy
-they are viruses that have an RNA genome and can code for proteins that produce
DNA from their RNA and insert it into the DNA of the cell
-however, viruses usually cause disease and even when inactivated, altered
particles may be able to recombine with viral DNA that already exists in the
individual being treated and lead to the formation of a new infectious strain
Method of introducing alleles into
human cells using engineered viruses
(4 steps)
1. Engineered retrovirus has recombinant RNA containing viral and human
2. Recombinant genes enter host cell.
3. Viral enzymes make double-stranded DNA version of introduced genes (reverse
4. Recombinant genes are inserted into host chromosome and transcribed.
-severe combined immunodeficiency
-lack normal immune system, cannot fight off infections
-“the boy in the bubble
-defective gene for receptor protein necessary for development of T cells
Gene therapy with SCID (3 steps)
1. Stem cells are isolated from the patient’s bone marrow and grown in vitro.
2. Recombinant retroviruses carry the normal allele into host cells.
3. Cells that are expressing normal alleles are isolated and implanted into patient.
Problems with this
-two of the ten boys they initially treated developed cancer characterized by
unchecked growth of T cells
-a viral-borne receptor gene had been inserted near the gene for a regulatory
transcription factor that triggers growth of T cells cancer
-although they managed to treat it, the researchers proposed to halt their trial of
the therapy to carefully assess the risks and benefits
Agrobacterium induces gall
-the gall/tumourlike growth at bottom of plant’s stem, is due to bacterial infection
1) Agrobacterium cells contain a Ti (tumour-inducing) plasmid
2) A section of DNA from the Ti plasmid called T-DNA incorporates into the
chromosomes of plant cells infected by the bacterium.
3) When transcribed, Ti genes induce the affected cell to begin growing and
dividing. The resulting gall encloses an increasing number of Agrobacterium cells.
Biol 121 225
Freeman 390-395, 407-411, 417-424 Mar. 3, 10
Golden rice goal of researchers?
Role of enzymes
Role of Ti plasmid
Other steps
-want golden rice to produce beta-carotene in the endosperm of seeds (rice)
-three enzymes are involved to synthesize B-carotene in endosperm
-expose embryos to Agrobacterium cells containing genetically modified Ti
plasmids (containing the genes for the enzymes)
-the transformed plants were then grown in the greenhouse
-some rice grains had so much B-carotene that they were “golden”
-this is good for vitamin A deficiency
Problems with GMOs
-GMO = genetically modified organism
-plants produce insecticides that can kill unintended organisms
-pollen transforms genes, transfers to other populations or even other species
-allergies can arise
Landmine detectors = plants
Arabidopsis thaliana
-thale grass the ‘fruit fly’ of the plant kingdom (as in, lots of genetic experiments)
-under stress, it turns red
-genetically modified so that NO2 (found in landmines) causes them to turn red
-therefore, growing the modified thale grass on postwar lands can help detect
mines so that they can be removed carefully
Forensics DNA fingerprinting
-DNA from different humans is 99.9% the same, closer than any other species
-only 1/100,000 of DNA are actually genes
-the rest are introns and repeated sequences
-the number of repeats varies, and may change over time
-separate satellites in gel electrophoresis based on the number of STR single
tandem repeats
Will genetics destroy sports?
Gene for growth factor.
-the gene for growth factor can be injected into mice via a virus vector
-damaged muscle is repaired and after a rigorous training program (strap weights
to legs and make it run), the mouse muscle mass increases one third compared to
controls without the injections