Changing genes

Question 1

What is selective breeding?

Answer 1

The process by which humans artificially select organisms with desirable characteristics and breed them to produce offspring with similar phenotypes

Question 2

Outline the main steps involved in selective breeding

Answer 2

1. Identify a desired characteristic e.g. disease resistance
2. Select parent organisms that show the desired traits and
   breed them together
3. Select offspring with the desired traits and breed them
   together
4. Process repeated until all offspring have the desired traits

Question 3

What is the main advantage of selective breeding?

Answer 3

Creates organisms with desirable features:
● Crops produce a higher yield of grain
● Cows produce a greater supply of milk
● Plants produce larger fruit
● Domesticated animals

Question 4

Other than in agriculture, where else is selective

breeding useful?

Answer 4

● In medical research

● In sports e.g. horse racing

Question 5

Outline the disadvantages of selective breeding

Answer 5

● Reduction in the gene pool (which becomes especially
harmful if sudden environmental change occurs)
● Inbreeding results in genetic disorders
● Development of other physical problems e.g. respiratory
problems in bulldogs
● Potential to unknowingly select harmful recessive alleles

Question 6

How can plants be cloned?

Answer 6

● Taking plant cuttings

● Tissue culture

Question 7

What is tissue culture?

Answer 7

A method of growing living tissue in a

suitable medium.

Question 8

Describe how plants are grown using tissue culture

Answer 8

1. Select a plant that shows desired characteristics
2. Cut multiple small sample pieces from meristem tissue
3. Grow in a petri dish containing growth medium
4. Transfer to compost for further growth

Question 9

What must be ensured when preparing tissue

cultures?

Answer 9

Ensure aseptic conditions to prevent

contamination by microorganisms

Question 10

What does the growth medium contain?

Answer 10

Nutrients and growth hormones

Question 11

What are the advantages of growing plants by tissue

culture?

Answer 11

● Fast and simple process
● Requires little space
● Enables the growth of many plant clones with the same
desirable characteristics
● Useful in the preservation of endangered plant species

Question 12

What are the disadvantages of growing plants by

tissue culture?

Answer 12

● Reduction in the gene pool
● Plant clones often have a low survival rate
● Could unknowingly increase the presence of harmful
recessive alleles

Question 13

Why is animal tissue culturing useful?

Answer 13

● Useful in the preparation of tissue samples for
medical research
● Enables the investigation of how different factors may
affect a specific animal tissue, without harming the
animal itself

Question 14

Describe how animal tissue cultures are prepared

Answer 14

1. Extract a sample of tissue from an animal
2. Use enzymes to separate cells within the sample
3. Grow in a culture vessel containing growth medium
4. Once grown, store the sample

Question 15

What is genetic engineering?

Answer 15

● The modification of the genome of an organism by the
insertion of a desired gene from another organism
● Enables the formation of an organism with beneficial
characteristics

Question 16

Describe the process of genetic engineering

Answer 16

1. DNA is cut at specific base sequences to cut out required gene by restriction enzymes to create sticky ends
2. Vector DNA (plasmid, virus) cut using the same restriction enzymes to create
   complementary sticky ends
3. Ligase enzymes join the sticky ends of the isolated gene and vector forming recombinant DNA
4. The vector inserts the Recombinant DNA into required cells

Question 17

What is a vector?

Answer 17

A structure that delivers the desired gene
into the recipient cell e.g. plasmids,
viruses

Question 18

Describe the benefits of genetic

engineering

Answer 18

● Increased crop yields for growing population e.g.
herbicide-resistance, disease-resistance
● Useful in medicine e.g. insulin-producing bacteria, anti-thrombin
in goat milk
● GM crops produce scarce resources e.g. GM golden rice
produces beta-carotene (source of vitamin A in the body)

Question 19

Describe the risks of genetic engineering

Answer 19

● Long-term effects of consumption of GM crops unknown
● Negative environmental impacts e.g. reduction in biodiversity, impact
on food chain, contamination of non-GM crops forming ‘superweeds’
● Late-onset health problems in GM animals
● GM seeds are expensive. LEDCs may be unable to afford them or
may become dependent on businesses that sell them.

Question 20

What is Bacillus thuringiensis (Bt)?

Answer 20

● Insect larvae are harmful to crops
● Bt is a bacterium which secretes a toxin
that kills insect larvae

Question 21

How is genetic engineering used to protect crops

against insects?

Answer 21

● The gene for toxin production in Bt can be
isolated and inserted into the DNAof crops
● Bt crops now secrete the toxin which kills any
insect larvae that feed on it

Question 22

What are the benefits of Bt crops?

Answer 22

● Increased crop yields (fewer crops damaged)
● Lessens the need for artificial insecticides
● Bt toxin is specific to certain insect larvae so is
not harmful to other organisms that ingest it

Question 23

What are the risks of Bt crops?

Answer 23

● Long term effects of consumption of Bt crops
unknown
● Insect larvae may become resistant to the Bt toxin
● Killing insect larvae reduces biodiversity

Question 24

Outline the agricultural methods of increasing food

production

Answer 24

● Intensive farming methods e.g. ‘battery’ farming
and the use of fertilisers and pesticides
● Biological control

Question 25

What is the main advantage of intensive farming?

Answer 25

Increases crop yields

Question 26

What are the disadvantages of intensive farming

methods?

Answer 26

● Fertilisers can wash into nearby water sources and cause
eutrophication
● The use of herbicides and insecticides reduces
biodiversity
● ‘Battery’ farming is often seen as unethical

Question 27

What is biological control?

Answer 27

When a new organism (often a predator)
is introduced into an ecosystem to
control a pest or pathogen

Question 28

What are the advantages of using biological control

to increase food production?

Answer 28

● The results of biological control generally last
for a long period of time
● The effects on wildlife are less severe

Question 29

What is the risk of using biological control?

Answer 29

Risk of the control organism becoming a

pest itself

Question 30

Advanced Information

Describe the process of genetic engineering in Bacteria

Answer 30

1. DNA is cut at specific base sequences to cut out required gene by restriction enzymes to create sticky ends
2. A plasmid is cut out from a bacterial cell, using the same restriction enzymes to create complementary sticky ends
3. The useful gene is mixed with the plasmids. Ligase enzyme join the sticky ends of the isolated gene and the plasmid forming a recombinant plasmid
4. The recombinant plasmid is put back into the bacteria and leave it to divide asexually.
5. This makes many copies of the bacteria which all contain the recombinant plasmid and produce the useful product.