Gene technologies

Genetic engineering creates a GMO (genetically modified organism) by inserting a useful gene from one organism into another. Steps for bacteria:

1. A restriction enzyme cuts the gene from donor DNA in a staggered way, leaving short single-stranded sticky ends.
2. The same enzyme cuts open a bacterial plasmid, giving complementary sticky ends.
3. Gene and plasmid are mixed; hydrogen bonds form between the sticky ends, then DNA ligase seals the joins, making a recombinant plasmid.
4. The recombinant plasmid (the vector) is inserted into a bacterium, which can now express the useful gene.

Products from GM bacteria: insulin (diabetes), penicillin (antibiotic), rennin (cheese-making) and factor VIII (haemophilia treatment).

GM plants use the bacterium *Agrobacterium tumefaciens* with its Ti plasmid as the vector, since plant cells have no plasmids.

Benefits in medicine: large-scale production of human proteins with few side effects. Risk: long-term consequences are not yet fully known.

Stem cells are undifferentiated cells that can self-renew (by mitosis) and differentiate into specialised types:

• Totipotent (very early embryo, e.g. zygote): can form a complete organism including the placenta.
• Pluripotent (embryonic stem cells): can become any body cell type but cannot form the placenta.
• Multipotent (adult stem cells, e.g. bone marrow): can only differentiate into a limited range of cell types.

Induced pluripotent stem cells (iPSC): adult body cells reprogrammed in the lab to act like pluripotent cells. No embryo is destroyed; if derived from the patient's own cells, immune rejection is avoided.

Medical applications (with risks):

• Bone marrow transplants → treat cancers (risks: increased cancer risk; immune rejection of transplanted cells).
• Replace pancreatic insulin-secreting cells → treat diabetes.
• Replace damaged skin → treat burns.
• Replace damaged neurones → treat spinal cord injury.
• Replace damaged heart muscle after a heart attack.

Selective breeding chooses parents with desired characteristics over generations. Unlike natural selection (driven by the environment), humans do the selecting, which can reduce genetic variation in a population.

• Confusing the stem-cell types (embryonic are the most versatile, adult are limited).
• Mixing up the roles: restriction enzymes cut, ligases join.