4.4 Genetics, Engineering and Biotechnology

Question 1

Define and describe polymerase chain reaction (PCR)

Answer 1

• PCR is a way of producing large quantities of a specific target sequence of DNA.
  
  • It is useful when only a small amount of DNA is available for testing (e.g. crime scene samples of blood, semen, tissue, hair, etc.)
  • Used to amplify small samples of DNA in order to use them for DNA profiling, recombination, species identification or other research

Question 2

Outline the process of polymerase chain reaction (PCR)

Answer 2

1. Heating in a thermal cycler denatures hydrogen bonds, separating the DNA into two strands and exposing bases
   
   2. The mixture cools and primers are added to the start of the target gene sequence
   3. A heat tolerant DNA polymerase (TAQ) replicates the DNA using free floating nucleotides in the mixture complementary base pairing
   4. The cycle is repeated many times, until there are millions of copies - enough to amplify even tiny samples found at a crime scene

Question 3

State what happens in gel electrophoresis

Answer 3

Through gel electrophoresis, fragments of DNA are moved through an electric field and separated based on their size. This works because DNA has a slight negative charge due to the phosphate on the backbone.

Question 4

Outline the process of gel electrophoresis

Answer 4

1. DNA samples taken and amplified with PCR
   
   2. Restriction enzymes cut DNA into fragments at specific base sequences in each sample
   3. Fluorescent marker binds to a triplet (three-base sequence) in the DNA fragments, so that results can be seen
   4. Samples placed in wells in the gel
   5. Gel placed in electrophoresis chamber and covered with buffer solution
   6. Electric current passed through, pushing the fragments along
   7. Smaller fragments are less impeded by the gel matrix and so travel further
   8. A DNA profile can then be made and compared with others

Question 5

Define DNA profiling

Answer 5

A technique by which individuals are identified on the basis of their respective DNA profiles.

Question 6

Define microsatalite

Answer 6

Short sequences of non-coding DNA.

Question 7

Outline the process of DNA profiling

Answer 7

1. DNA extracted and amplified with PCR
   
   2. Microsatellites cut with restriction enzymes
   3. Specific restriction enzymes used on microsatellites
   4. Fragments separated with gel electrophoresis
   5. DNA profile can then be analysed

Question 8

State two uses for DNA profiling

Answer 8

Determining paternity and forensic investigation

Question 9

Describe how DNA profiling can be used for determining paternity

Answer 9

• DNA samples taken from mother, child and potential fathers.
  
  • All the DNA fragments from the child must match with either the mother or father

Question 10

Describe how DNA profiling can be used for forensic investigation

Answer 10

• DNA taken from the victim, crime scene and suspects

* Bands compared to distinguish between the suspect and victim DNA

Question 11

State three outcomes of sequencing of the complete human genome

Answer 11

• Knowledge of the number and location of human genes
• Discovery of proteins and their functions
• Evidence of evolutionary relationships

Question 12

Outline the significance of finding the number and location of human genes by sequencing the complete human genome

Answer 12

There are around 30,000 genes in the human genome. This is fewer than expected, so there must be more complex relationships between genes. This allows for targeted research and diagnostics, as well as therapies.

Question 13

Outline the significance of discovering proteins and their functions by sequencing the complete human genome

Answer 13

We know of more proteins and their functions, as well as the base sequences which code for them. Therefore, we can use transgenics to move beneficial genes from one species to another, or to use them to target research and medicine - even design new proteins.

Question 14

Outline the significance of discovering evidence of evolutionary relationships by sequencing the complete human genome

Answer 14

Closely related species share a lot of the base sequence of their genomes. Distant relatives share less. By sequencing genomes, we have further, more reliable evidence of evolution and are able to put species into more appropriate taxa.

Question 15

Outline how genetic code is universal

Answer 15

• All living thins use the same bases and the same genetic code
  
  • All known organisms use the same nucleic acids to code for proteins
  • In principle, if we transfer a gene from one species to another, it should be transcribed and translated into the same protein

Question 16

Outline a basic technique used for gene transfer

Answer 16

• A plasmid is removed from a bacterial cell
  
  • A gene of interest is removed from an organism’s genome using a restriction endonuclease which cuts at specific sequences of DNA
  • The gene of interest and plasmid are both amplified using PCR
  • The plasmid is cut with the same restriction enzyme that was used to remove the gene of interest
  • Cutting with certain restriction enzymes may generate short sequence overhangs (“sticky ends”) that allow the two DNA constructs to fit together
  • The gene of interest and plasmid are spliced together by the enzyme DNA ligase creating a recombinant plasmid
  • The recombinant plasmid is inserted into a new bacterium
  • The transgenic cell will hopefully express the desired trait encoded by the gene of interest

Question 17

State three examples of uses of genetically modified crops

Answer 17

• Golden rice is enriched with beta-carotene, which is converted into vitamin A in the body, helping to prevent malnutrition-related blindness in developing countries.
• Insect-resistant corn produces proteins which pests do not like, therefore toxic insecticides are not needed on the farm
• Salt resistant tomatoes can be grown in saline soils

Question 18

State an example of a use of genetically modified animals

Answer 18

Factor IX-producing sheep produce human clotting factors in their milk, for use in the treatment of haemophilia

Question 19

State four benefits potential benefits of genetically modified crops

Answer 19

• Increased yields of crops and faster breeding cycles
• Crops can be grown in harsher environmental conditions
• Reduced need for pesticides which can harm human and environmental health through biomagnification
• Nutrient-enhanced crops in areas of high food pressure or famine

Question 20

State four potential harmful effects of genetically modified crops

Answer 20

• Potential genetic pollution of organic crops through fertilisation by pollen of GM crops
• Unknown health risks of some crops
• Feat of monopoly-like behaviour as farmers need to buy expensive seeds annually
• Potential hybridisation of related species

Question 21

Define clone

Answer 21

A group of genetically identical organisms OR a group of genetically identical cells derived from a single parent cell

Question 22

Outline a technique for cloning using differentiated animal cells

Answer 22

Somatic Cell Nuclear Transfer (SCNT)

1. Remove a differentiated diploid nucleus from individual to be cloned
2. Enucleate a donor egg cell 
3. Insert he diploid nucleus into the enucleated egg cell
4. Implant into the endometrium of a surrogate and gestate
5. The new born will be genetically identical to the nucleus' parent

Question 23

State four arguments for therapeutic cloning in humans

Answer 23

• Transplants less likely to be rejected as they are genetically identical to the patient
• Could be used to cure otherwise incurable diseases
• Stem cells can be taken from embryos that have stopped developing and would have died anyway (e.g. abortions)
• Cells are taken at a stage when the embryo has no nervous system and can feel no pain

Question 24

State four arguments against therapeutic cloning in humans

Answer 24

• Involves the creation and destruction of human embryos (at what point do we afford the right to life?)
• Religious or moral objections to ‘playing God’
• More embryos are generally produced than are needed, so excess embryos are ‘killed’
• With additional cost and effort, alternative technologies may fulfil similar roles (e.g. nuclear reprogramming of differentiated cell lines)