3.5 genetic modification and biotechnology

Purpose of PCR

To produce large quantities of a specific target sequence of DNA/ amplify small samples of DNA

What process does PCR mimic

DNA replication

Functions of each reagent in PCR (Primers, Taq polymerase, nucleotides)

Primers: attach to opposite ends of the target sequence

Taq polymerase: copies the strands

nucleotides: synthesises new DNA strands

Outline how gel electrophoresis works

1. DNA samples are taken and amplified with PCR

2. Restriction enzymes cut DNA into fragments at specific base sequences in each sample

3. A fluorescent marker binds to a triplet in the DNA fragments, so that results can be seen

4. Samples are added to a gel electrophoresis chamber. Electric current is passed through, pushing the fragments along

5. Heavier fragments stay closer to the origin and smaller fragments go further

6. A banding pattern shows up for each DNA sample and can be compared

Uses of DNA profiling (2)

Forensics and paternity tests

What is genetic modification

Inserting a gene from one species into the genome of another species

the new organism created is called a transgenic

Explain why transfer of genes between species is possible using the idea of the universal genetic code

• All living things use the same bases and the same genetic code

• Each codon produces the same amino acid so the amino acid sequence remains unchanged

Examples of gene transfer in animals and plants

• milk containing spider silk protein is produced by goats (spider silk is immensely strong)

• Human insulin produced by bacteria for diabetics

• Golden rice is coloured yellow as it contains βcarotene (a precursor to vitamin A)

• Salt tolerant tomato plants

Steps of gene transfer

1. DNA Extraction

   • Gene of interest isolated from organism

   • Gene is amplified using PCR (along with a plasmid)

2. Digestion and Ligation

   • Plasmid and gene cut with a specific restriction enzyme

   • Gene is spliced into plasmid vector by DNA ligase

3. Transformation and Expression

   • Recombinant plasmid is inserted into a host cell

   • Antibiotic selection may be used to select for successful transgenic cells (if plasmid has an antibiotic resistance gene)

   • Transgenic cells express new protein (for extraction/use)

Function of restriction enzymes in gene transfer

To ‘cut’ the desired gene from the genome

What are ‘sticky ends’

Strands of DNA that overhang from the other side with their bases exposed

Function of reverse transcriptase

To transcribe/revert mRNA into DNA

Function of DNA ligase

Joins human insulin gene to plasmid

It brings all the molecules of the newly formed DNA or RNA strands together and permanently binds them with a phosphodiester bond, so that they dont just fall apart

State the process used to amplify the small amounts of DNA collected at the crime scene to an amount big enough to be used in DNA profiling.

PCR

Explain the potential benefits of GM crops to the environment, human health and agriculture

Benefits

• Introduction of a new trait

• Results in increased productivity – less land used / greater yield / less crop damage

• Less use of chemical pesticides – reduced cost / ecological damage to wild the economic cost of farming

• Increased disease resistance

• Less use of chemical herbicides

• Less use of chemical fertiliser

• Increased hardiness – better drought/cold slinity tolerance and therefore can be grown in more locations / has a longer growing season

Explain the potential risks of GM crops to the environment, human health and agriculture

• Could be toxic to or cause allergic reactions in humans- Transferred genes could mutate after testing

• Non-target organisms affected by toxins

• Increased resistance to toxin evolves in pests

• Accidental release may result in competition with native plant species

• Super weeds - through cross-breeding the introduced gene could be transferred to wild varieties

• Biodiversity reduced – both plant populations by direct competition and animal populations directly and indirectly could be affected

• Patent laws prevent farmers producing locally suitable varieties – this would lead to unregulated field tests, not a desirable situation

Example of a GMO crop and its characteristics

Bt corn

• Bacillus thuringiensis (Bt) is a soil bacterium that produces insecticidal toxins

• Genes from Bt have been inserted into maize so GM plants can produce an insecticidal toxin and therefore be resistant to pests

Potential benefits of Bt corn

• Introduction of a new trait- Bt Corn is significantly more resistant to pests

• Results in increased productivity – Maximum productivity has not increased, but losses in ‘bad’ years have been reduced

• Less use of chemical pesticides – Bt toxins are considered to be much more selective and safer for humans and non-target organisms than most conventional insecticides

Potential risks of Bt corn

• Could be toxic to or cause allergic reactions in humans

• Non-target organisms affected by toxins

• Accidental release may result in competition with native plant species

• Super weeds - there is evidence of superweeds evolved from other transgenic crops

• Biodiversity reduced

Differentiate between asexual and sexual reproduction

Sexual reproduction involves the fusion of male and female gametes whereas asexual reproduction does not require male and female individuals and no fusion of gametes takes place.

Asexual reproduction always results in clones

State the definition of the term clone

A group of genetically identical organisms.

A group of cells derived from a single parent cell.

Examples of naturally occurring clones

• Starfish, if damaged, can regenerate a whole body from a single leg

• asexual reproduction, such as binary fission in bacteria

• Runners (plant) are modified laterally growing stems used to reproduce asexually. Each new plantlet can separate to produce a new plant

• Tubers (plant), the swollen tips of underground stems, are storage organs in plants such as sweet potatoes. During winter the plant dies back, but in spring each tuber starts to grow producing separate plants, all clones of the parent plant

Briefly explain how and why animals can be cloned at the embryonic stage

Embryos can split and then continue to develop separately

This is possible because in embryonic development the cells are still unspecialised can become any type of cell (pluripotent)

State the definition of the term differentiated diploid nucleus

nucleus of somatic (body) cells that is unspecialized and can differentiate into different types of cells.

Steps of Somatic Cell Nuclear Transfer (SCNT)

1. Remove a differentiated diploid nucleus from the individual to be cloned.

2. Enucleate a donor egg cell.

3. Insert the diploid nucleus into the enucleated egg cell.

4. Implant into the endometrium of a surrogate mother and gestate.

5. The newborn will be genetically identical to the donor nucleus parent.

Steps of therapeutic cloning

1. Remove a differentiated diploid nucleus from the cell to be cloned.

2. Enucleate a donor egg cell.

3. Insert the diploid nucleus into the enucleated egg cell.

4. Stimulate it to divide and grow in vitro.

5. The resulting embryo is a rich source of stem cells which can be harvested or cultured.

6. The outer layer of cells is removed, so only the Nuclear transfer animation from HHMI: inner cell mass is used to culture the tissues needed.

List some reasons how cloning can be useful

• Create stem cells for transplants, such as in burns patients or leukemia.

• Replace other damaged tissues such as nerves, pancreas cells etc.

• Much reduced risk of rejection of cells as they are genetically identical to the recipient