Genetic Engineering

Polymerase Chain Reaction (PCR) Fig. 16.3 in text

• a technique for quickly cloning a particular piece of DNA in the test tube (rather than in living cells like E. coli).

• Very useful if only have small quantities such as blood or semen.

• Use temperature changes to separate the DNA strand, add primers, polymerase and ta-dah... new strand is made.

Gel Electrophoresis and DNA Profiling. Fig 16.2 in text

• Method using electricity to separate fragments of DNA– fragments are made by using restriction enzymes

• Large segments of DNA (negatively charged) can’t move through gel very far while small ones can.

• In agarose gels, fragments of DNA from about 200 to 50,000 bp can be separated

• The results from electrophoresis can be used for DNA profiling/fingerprinting – using the patterns of bands of DNA to identify and compare individuals.– Useful for identifying rapists, criminals, determine

paternity, determine relatives...

Genetic Screening

• The testing of an individual for the presence or absence of a gene

• Advantages – fewer children with genetic diseases are born

(a couple doesn’t reproduce or only selects “good” embryos for implantation)

– confirmation of animal pedigrees– if genetic diseases can be found early

enough, treatments can be given to prevent all or some of the symptoms of the disease

• Disadvantages – frequency of abortion may increase– harmful psychological effects– creation of a genetic underclass (refused

jobs, insurance, spouse...)

Genetically Modified Organisms • organisms that have had genes from a different

organism transferred to them• examples

– crops resistant to herbicides (but the weeds are not)

– insulin gene from humans is put in the plasmid of E. coli which then makes insulin

– a bacterium gene that codes for a protein called Bt toxin that kills moths that bore through corn is transferred to the DNA of corn

• Benefits– less pest damage– less land needed for crops– less use of insecticides

• Harmful effects– humans/animals my be harmed by toxin– other non-corn eating insects could be killed

by pollen from the corn– cross-pollination could spread the toxic gene

to some wild corn that would then have an advantage over other natural species

Gene Therapy • the treatment of diseases by

altering the defective genotype of the organism

• example: SCID (severe combined immune deficiency)– screening before birth can

show SCID – the enzyme ADA that is

necessary to make healthy lymphocytes is not made

• lymphocytes, a type of white blood cell, are made from blood forming precursors, or "stem," cells in the bone marrow

– the allele that codes for ADA is obtained and the gene is inserted into a retrovirus

– the retroviruses insert the gene into the stem cells’ chromosomes

– new stem cells containing working ADA gene are injected into the person

Clones • a group of genetically identical organisms or cells

artificially derived from a single parent cell• ex) Dolly

– cells were taken from a donor sheep and the nucleus removed

– eggs from another sheep were taken and the nuclei were removed

– donor cells and nuclei were fused together using electricity and then developed into embryos that were implanted into a surrogate mother

– a lamb was born (Dolly) that was genetically identical to the donor sheep

• ethical issues in humans– Pros

• happens naturally with twins• infertile couples might have better chance

of success with cloning of embryos– Cons

• psychological/identity problems for groups of genetically identical people

• cells used in cloning have already begun to age and therefore cloned humans may age faster

• lead to selection of a super-race of those fit to be cloned