Transgenesis Transferring a gene(s) from one species to another Introduce desirable traits not normally be present in a species. Genetic modification
Techniques used • Restriction digestion (cut desired gene) • Ligation (insert desired gene into vector) • Whole animal OR Gene cloning
GM Animals • Modified DNA introduced into fertilised egg all new cells, including gamete producing cells are transgenic - will be inherited OR • Normal gene inserted into somatic tissue to correct a genetic deficiency – not inherited (gene therapy) • Livestock able to produce human proteins.
Methods of animal transgenesis • electroporation: brief electric shock opens pores in plasma membrane and allows DNA to be taken up from medium • viral carrier: transduction after viral DNA is made harmless • lipofection: DNA coated with minute lipid vesicles (liposomes) which are endocytosed • microinjection: using micropipette(low success)
Cows Milk Cows can produce relatively large quantities of protein. Inserting genes into the cows to produce modified milk can be relatively easy. Genes inserted to produce milk with improved: • calf nutrition and disease resistance • resistance against mastitis • benefits for human health • commercial possibilities
Example Application Human Myelin Basic Protein - essential protein in the myelin sheath that insulates and protects neurones – absent in Multiple Sclerosis. • previously from blood products or cadavers – slow, expensive and could be contaminated • GM milk protein extracted therapeutic drugs • fast production of large amounts of protein • cheaper than previous methods • less objectionable than cadavers and blood??
Example Application Casein is a naturally occurring milk protein used in cheese production • Gene inserted so cows milk contains more casein more milk solids • more efficient, cost-effective cheese production • products such as infant milk powder production • could become cheaper BUT • currently benefits offset by cost • weight gain / diseases associated with excess casein
Example Application Chymosin (rennin) used to manufacture food products that require clotted milk • previously obtained from calf stomachs • Now incorporated into transgenic bacteria / yeast • totally hygienic • large quantities any time of year (yeast reproduce freely) • identical to natural calf chymosin • more acceptable to vegetarians? BUT: • Yeast/bacteria may mutate and not function correctly
GM Plants • Improved characteristics such as resistance to pests and diseases • Modified characteristics such as vitamin A synthesis in crops – nutritionally superior • Increased productivity - GM crops larger • Anti-GM lobbyists: risk of contamination of organic farms, creation of super-weeds and the potential extinction of wild plants.
Methods of Plant transgenesis • Protoplast fusion – cell with cell wall digested = protoplast (2 protoplasts fuse double DNA) • Biolistics/ DNA gun - microscopic particles of gold or tungsten coated in transgene DNA propelled into cell • Plasmid or viral vectors - recombinant DNA transferred via vectors. None of these methods are fully successful
Protoplast fusion Enzymes digest cell walls 2 diploid cells fuse cell with double DNA
Particle gun method vector method
Agrobacteriumtumefaciens Gall disease bacterium • enters wounded tissue • inserts tumour-inducing (Ti) plasmid into plant • T-DNA incorporated into host chromosome • stimulates cell division Plasmid is prepared by: • removing the tumor gene • adding antibiotic resistance gene (as a marker) Medium with antibiotic kills off unmodified cells