3.5 Genetic modification

Question 1

gel electrophoresis

Answer 1

used to separate proteins or fragments of DNA according to size

Question 2

uses of gel electrophoresis

Answer 2

analyse DNA in DNA profiling, diagnosis of genetic diseases

Question 3

PCR (polymerase chain reactions)

Answer 3

used to amplify small amounts of DNA so that there is enough DNA to do an analysis

Question 4

outline the process of PCR

Answer 4

1. temperature is raised to 95 to cause the double-stranded DNA to separate into single strands
2. temperature is decreased to 53 for DNA primers to anneal to complimentary matches on the target DNA sequence
3. the primers bracket the target sequence to be copied
4. at 73, the enzyme Taq polymerase binds to the primer sequences and adds nucleotides to extend the second strand

Question 5

DNA profiling

Answer 5

involves comparison of DNA

Question 6

process of DNA profiling

Answer 6

1. a sample of DNA is obtained
2. sequences in the DNA that vary considerably are selected and copied by PCR
3. the copied DNA is split into fragments using restriction endonucleases
4. the fragments are separated using gel electrophoresis
5. this produces a pattern of bands that is always the same with DNA taken from one individual
6. comparisons of DNA profiles

Question 7

genetic modification

Answer 7

allows genes to be transferred between species

Question 8

process of genetic modification

Answer 8

plasmid removed from bacteria; 
plasmid cleaved open by restriction enzymes; 
desired DNA extracted from donor; 
DNA from donor cleaved using same restriction enzyme; 
results in sticky ends; 
with complementary base sequences; 
pieces of DNA from two organisms mixed; 
ligase used to seal up pieces; 
recombinant plasmids formed; 
insertion into host cells

Question 9

process of gel electrophoresis

Answer 9

1. An electric field is applied to the gel by attaching electrodes to both ends.
2. Depending on whether the particles are positively or negatively charged, they move towards one of the electrodes or the other; the gel resists the movement of particles.
3. The rate of movement depends on the size of the molecules - small molecules move faster than larger ones and further in the given time.

Question 10

uses of PCR

Answer 10

Very useful when very small quantities of DNA are found in a sample and larger amounts are needed for analysis
DNA from blood, semen or hairs can be amplified for use in forensic investigations
PCR allows particular desired sequences to be copied from a whole genome or even greater mixture of DNA
Used to copy specific DNA sequences: a sequence is selected for copying by using a primer that binds to the start of the desired sequence by complementary base pairing

Question 11

uses of DNA profiling

Answer 11

Blood stains on a suspect’s clothing could be shown to come from the victim
Blood stains at the crime scene that are not from the victim could be shown to come from the suspect
A single hair at the crime scene could be shown to come from the suspect
Semen from a sexual crime could be shown to come from the suspect
Each example is compared with the DNA profile of a sample of DNA taken from the suspect or the victim
If the pattern of bands matches exactly it is highly likely that the two samples of DNA are from the same person → provides a strong evidence of who committed the crime

Question 12

Risks and benefits of GM crops

Answer 12

Benefits:

• The nutritional value of crops can be improved (eg. increasing the vitamin content)
• Edible vaccines are produced so by eating the crop a person would be vaccinated against a disease
• Less insecticide has to be sprayed on to the crop so fewer bees and other beneficial insects are harmed
• Reduces the need for plowing and spraying crops, so less fuel is needed for farm machinery
• Varieties resistant to drought, cold and salinity are produced, expending the range over which crops can be produced and increasing total yields
• Crop varieties that are resistant to diseases caused by viruses are produced

Risks:

• Proteins produced by transcription and translation of transferred genes could be toxic or cause allergic reactions in humans or livestock
• Transferred genes can mutate and cause unexpected problems that were not risk assessed during development of GM crops
• Non-target organisms could be affected by toxins that are intended to control pests in GM crop plants
• Genes transferred to crop plants to make them herbicide resistant could spread to wild plants
• Some seed from a crop is always split and germinates to become unwanted volunteer plants that must be controlled

Question 13

Risks of Bt Corn

Answer 13

A gene was transferred from the bacterium that codes for Bt toxin which kills members of insect orders that contain butterflies, moths, flies, beetles, bees and ants
The genetically engineered corn varieties produce Bt toxin in all parts of the plant including pollen
Concerns: can target non-target species
Risk that monarch larvae might be poisoned by Bt toxin in pollen from GM corn crops

Question 14

Cloning

Answer 14

production of genetically identical organisms

Question 15

process of cloning by somatic-cell nuclear transfer

Answer 15

cell taken from udder of donor adult and cultured in laboratory for six days
unfertilised egg taken from another sheep. nucleus removed from the egg.
egg without a nucleus fused with donor cell using a pulse of electricity
embryo resulting from fusion of udder cell and egg transferred to the uterus of a third sheep which acts as a surrogate mother
surrogate mother gives birth to lamb