Genetic modification and biotechnology

Question 1

What is PCR and how does it work?

Answer 1

• Polymerase chain reaction (PCR), replicate large quantities of DNA from a small initial sample
  Check steps in book

Question 2

How much DNA is doubled with every cycle of PCR?

Answer 2

• Using equation 2^n
• n= number of cycles
• E.g. initial = 10ng
  10 x 2^5 = 320ng

Question 3

What is Gel electrophoresis used for?

Answer 3

• Separates and isolates proteins or DNA fragments based on mass or size, used after PCR
• DNA samples placed in a block of gel, electric current passed through, since DNA is negatively charged, move towards cathode +
• Smaller pieces move faster through the gel, causes samples of different sizes to separate

Question 4

What is satellite DNA?

Answer 4

• Short DNA sequences, number of repeats vary between individuals
• They can be divided into fragments by restriction enzymes
• Used in DNA profiling
• They include short tandem repeats (STR)

Question 5

What is DNA profiling? What are STRs?

Answer 5

• Individuals can be identified and compared via their respective DNA profiles
• The short tandem repeats (STRs) are used which are non-coding regions that make up long stretches of DNA
• Individuals will have different number of repeats at a specific DNA locus

Question 6

How is DNA profiling used in paternity and forensic investigations?

Answer 6

1. DNA sample collected and amplified using PCR
2. Satellite DNA (including STR sequences) are cut with restriction enzymes to generate fragments
3. Fragment length will differ between individuals since the STR also vary in length
4. Fragments separated using gel electrophoresis and resulting profiles compared

Question 7

How is DNA profiling used in forensic investigations and how in paternity testing?

Answer 7

• Forensic: Suspects DNA matched with DNA evidence found at crime scene for a conviction to occur
• Paternity: Since children inherit half their chromosomes from each parent, have comparable DNA with mother and father

Question 8

Be able to analyse examples of DNA profiles.

Question 9

What is gene modification?

Answer 9

• Transfer of genes between species, new organism called transgenic
• Possible since humans have a common ancestor, genetic code is the same between species, universal

Question 10

What are the four main steps for genes transfer to occur in bacteria?

Answer 10

1. Isolation of gene and vector by PCR
2. Digestion of gene and vector by restriction endonuclease
3. Joining of gene and vector by DNA ligase
4. Selection and expression of transgenic construct

Question 11

Explain step 1 of gene transfer.

Answer 11

• DNA isolated from cells, heavy components separated
• Gene of interest is amplified by PCR
• A vector is a DNA molecule that is used as a vehicle to carry the gene of interest into a foreign cell
• Example of vector: bacterial plasmids, since they can self-replicate or viruses/artificial chromosomes

Question 12

Explain step 2 of gene transfer.

Answer 12

• The vector (plasmid) and gene of interest are cut with restriction enzymes at recognition sites to put the gene into the plasmid
• Restriction enzyme used: restriction endonucleases, generates sticky ends
• Either sticky ends or blunt ends

Question 13

Explain step 3 of gene transfer.

Answer 13

• Gene of interest is inserted into a plasmid vector that was cut with the same restriction endonucleases
• This happens because the sticky ends of the gene and vector overlap (complementary base pairing)
• Enzyme DNA ligase link gene and vector together to form a recombinant construct, they form covalent bonds

Question 14

Explain step 4 of gene transfer.

Answer 14

• The recombinant construct (plasmid) is inserted into a bacterial cell
• The cell will grow and reproduce
• Antibiotic selection is then used to identify which cells have successfully incorporated the recombinant construct

Question 15

What happens in antibiotic selection?

Answer 15

• To show it the plasmid is correctly incorporated, and if the gene is expressed
• If the bacteria is resistant, it will grow in the solution of antibiotics
• The transgenic cells (cell in which the DNA is inserted into), once isolated and purified will begin expressing the desired trait encoded by the gene
  Check book

Question 16

What are genetically modified organisms (GMOs) used for?

Answer 16

• In agriculture they improve crop yield to reduce farming costs

Question 17

What are three advantages of genetic modified organisms?

Answer 17

1. New positive traits introduced, any desired trait can be developed, adaptation to the current conditions and demands. E.g Golden corn, increase Vitamin A content (prevent blindness)
2. Provide greater yield, bring about economic advantages, greater profit and lower prices for consumers.
3. Higher yield means less land is needed, more natural ecosystems, less pesticide need to be sprayed

Question 18

What are four risks of genetic modified organisms?

Answer 18

• Modified species may out-compete native species or kill non-pest species, reduction of biodiversity
• Not all nations and farmers have access to the technology, increased pest attacks, increased inequality between farms
• Exposure to new genes could cause unknown impacts and damage to human health, allergic reactions
• Crops with pest toxin could accelerate the evolution of resistant pest species

Question 19

What is Bt corn and how does it put monarch butterflies at risk?

Answer 19

• Genetically modified maize that incorporates an insecticide producing gene from the bacterium Bacillus thuringiensis
• Insecticide is lethal to the corn larvae (before butterfly)
• Spread of the Bt (protein) corn cay impact survival rates of monarch butterflies
• Pollen of Bt also contain Bt toxin, spread to milkweed which is main source of food for monarch butterfly

Question 20

What study was done on Bt corn and monarch butterflies? What did the scientists change?

Answer 20

• 1999 preliminary study, suggested in a laboratory setting monarch caterpillars were more likely to die when feeding on milkweed plants that was dusted with pollen of Bt corn, higher mortality rates
• 2001, believed risk to monarchs from Bt toxin was minimal, no significant increase in mortality when placed in corn field
• Other reasons for mortality, climate change

Question 21

What are clones?

Answer 21

• Groups of genetically identical organisms or group of cells derived from a single original parent cell
• Asexual reproduction, genetically identical clones (sexually reproducing also with identical twins)
• Requires the production of stem cells

Question 22

What are the two methods of cloning?

Answer 22

• Splitting of an embryo to clone an animal before the cells have differentiated (natural)
• Somatic cell nuclear transfer (artificial)

Question 23

What is somatic cell nuclear transfer and how does it produce cloned embryos?

Answer 23

• Donor somatic body cells taken from the organism and cultured in the lab (cells are diploid)
• An unfertilized egg is taken from another individual and enucleated (nucleus removed)
• The enucleated egg cell is fused with the nucleus from the adult donor to make a diploid egg cell (with the donor’s DNA)
• Electric current is delivered to stimulate the egg to divide and develop into an embryo
• Embryo implanted into the uterus of a surrogate and will develop into a genetic clone of the adult donor

Question 24

What is the natural method of cloning?

Answer 24

• In animals the early stage of an embryo is composed of totipotent stem cells (can differentiate into any or all types of tissues)
• Embryos can be split, each fraction can be implanted into surrogate mothers. These split embryos can develop into clones of the original zygote and form normal organisms (identical twins)
• The offspring will retain the same features regardless of the characteristics of the surrogate mother, not genetically related

Question 25

For what is the method of using differentiated cells used?

Answer 25

• Reproductive cloning: the embryo is implanted into the uterus of a surrogate, a new cloned organism will develop
• Therapeutic cloning: embryonic cells can be induced to differentiate to create specific tissues or organs for transplantation (bone marrow)

Question 26

What are 4 methods of natural cloning in animals?

Answer 26

• Binary fission: chromosome copied and cell split in half, 2 cells with a copy of the chromosome e.g. flatworms
• Budding: cells split off the parent, generates a smaller daughter organism, separates from the parent e.g. yeast
• Fragmentation: new organisms grow from a separated fragment of the parent organism e.g. starfish
• Parthenogenesis: embryos are formed from unfertilized ova e.g. fish

Question 27

What are 2 natural methods of cloning in plants?

Answer 27

• Tubers can form new plants which are genetically identical to parent plant
• Garlic and onion bulbs are modified plant leaves, genetically identical

Question 28

What factors affect rooting of stem-cuttings?

Answer 28

• Allowing a stem cutting to root by putting it in water can produce a clone. Large number can be generated
  Factors:
• Internal: position of cutting, age of starring plant, surface area of leaves on stem cutting
• External: length & intensity of light exposure, temperature off cutting, concentration of rooting hormones

Question 29

How to design an experiment on factors affecting stem cutting?

Answer 29

• 1 Independent variable, select a range
• 1 Dependent variable, how you are going to measure it
• Research question
• Method, focus on controlled variables and repeat trials
• Collect and process data, how you will do this
• Include JUSTIFICATIONS