Topic 4: Natural Selection and Genetic Modification

Question 1

(4.1B) Who were the two main scientists that proposed the theory of evolution by Natural Selection?

Answer 1

Darwin: came up with the theory of evolution by natural selection, observed variation within members of the same species and that those with characteristics most suited to the environment were more likely to survive. He notes that these characteristics could be passed on and wrote ‘On the Origin of Species’
Wallace: scientist that worked at the same time as Darwin. Came up with the idea of natural selection, independently of Darwin. They published their papers together despite not always agreeing on mechanisms of natural selection. Wallace’s observations provided evidence with warning colours of butterflies to deter predators.
The theory of evolution by natural selection impacts modern biology through:
- classification, animals are now classified about how closely related they are as we know they all descended from a common ancestor
- antibiotic resistance, importance of finishing the coarse of drugs to prevent bacteria spreading, need to constantly develop new antibiotics to fight newly evolved resistant bacteria
- conservation, imortance of genetic diversity and how it helps populations adapt to changing environments

Question 2

4.2 Explain Darwin’s theory of evolution by natural selection

Answer 2

1) Genetic variation within a population due to differences in their alleles. New alleles arise due to mutations.
2) Things like predation, competition for resources and disease act as selection pressures. They affect an organism’s chance of surviving and reproducing.
3) Individuals with characteristics that make them better adapted to the selection pressures in their environment have a better chance of survival and so are more likely to breed successfully.
4) The alleles that are responsible for the useful characteristics are more likely to be passed on than the less well adapted that may be less likely to survive and reproduce.
5) The beneficial characteristics become more common in the population over time.

Question 3

4.3 Explain how the emergence of resistant organisms supports Darwin’s theory of evolution including antibiotic resistance in bacteria

Answer 3

1) Bacteria develop random mutations in their DNA
2) These create new alleles which change the bacteria’s characteristics
3) This could include the ability to resist certain antibiotics and this is a big advantage.
4) In a host who’s being treated to get rid of the infection, a resistant bacterium is better able to survive and so lives longer and reproduces more
5) This leads to the allele for antibiotic resistance being passed on to lots of offspring and this becomes more common in the population over time until the population all have antibiotic resistance

Question 4

4.4 Describe the evidence for human evolution, based on fossils, including: a) Ardi from 4.4 million years ago b) Lucy from 3.2 million years ago c Leakey’s discovery of fossils from 1.6 million years ago

Answer 4

a) Ardi from 4.4 million years ago
- feet structure suggest she climbed trees
- long arms and short legs (more ape than human)
- skull volume same as chimpanzee’s
- leg and hand bone structure suggest she walked upright and didn’t use hands to walk like apes do
b) Lucy from 3.2 million years ago
- arched feet suggest she walked
- arms and legs between human and ape length
- skull volume slightly larger, still similar to chimp
- bones and feet structure suggest she walked upright, more efficiently than Ardi
c) Leakey’s discovery from 1.6 million years ago
- Leakey discovered many fossils
- 1.6 million year old Homo erectus, mixture of human and ape-like features, more human than Lucy
- short arms and long legs, more human than ape
- skull volume closer to human brain size
- legs and feet even better adapted than Lucy

Question 5

4.5 Describe the evidence for human evolution based on stone tools, including: a) the development of stone tools over time b) how these can be dated from their environment

Answer 5

a) Stone tools gradually became more complex and so their brains must have been getting larger (cerebral cortex)
- Homo Habilis: simple stone tools by hitting rocks together to make sharp flakes, used to scrape meat from bones or crack rocks open
- Homo Erectus: Sculpted rocks into shapes to produce more complex tools like simple hand-axes, used to hunt, dig, chop and scrape meat from bones.
- Homo neanderthalenis: More complex tools, evidence of flint tools, pointed tools and woodden spears
- Homo sapiens: Flint tools used widely, pointed tools including arrowheads, fish hooks and needles around 50000
b) 1) Look at structural features, simpler tools are likely to be older
2) Use stratigraphy, study of rock layers, older rock layers below younger layers, if in deeper layers older
3) Carbon-14 dating for carbon containing materials such as a wooden handle to date material

Question 6

4.6B Describe how the anatomy of the pentadactyl limb provides scientists with evidence for evolution

Answer 6

1) A pentadactyl limb is a limb with five digits
2) You can see the pentadactyl limb in many species eg. mammals, reptiles, amphibians
3) In each the limb has a similar bone structure but different function, eg. human hand, bat wing
4) Similar bone structure proves evidence that species with a pentadactyl limb have all evolved from a common ancestor that had a pentadactyl limb

Question 7

Exam style question: Explain why scientists cannot be sure that human-like animals such as Ardi, evolved into modern humans.

Answer 7

Despite the trends in features of fossils found, there are many gaps in between the years they are thought to have originated from, meaning that scientists cannot be certain that each species evolved into the other.

Question 8

4.7 What are the three domains and their differences?

Answer 8

All of life can be divided into three domains, based on the type of cell of the organism

Bacteria: cells do not contain a nucleus, and have no unused sections in genes

Archaea: cells do not contain a nucleus; but are unique cause they have a different cell wall from bacteria, and their genes contain unused sections of DNA

Eukarya: cells do contain a nucleus, and their genes contain unused sections of DNA

Question 9

4.7 Describe how genetic analysis has led to the suggestion of the three domains rather than the five kingdoms classification method

Answer 9

Originally there were the 5 kingdoms. But the development of genetic analysis showed that all organisms apart from prokaryotes (no nucleus) have unused sections of DNA in their genes, that do not help with making a protein. When an exception to this rule was found; Archaea, found to have genes containing unused sections despite being a prokaryote. It was proposed that organisms should be divided into three domains instead.
Eukarya: (Eukaryotes that have unused sections of DNA)
Archae: (Prokaryotes that have unused sections of DNA)
Bacteria: (Prokaryotes that have NO unused sections of DNA)

Question 10

4.7 Describe the 5 animal kingdoms

Answer 10

Animals, Plants, Fungi, Protists, Prokaryotes

Question 11

4.8 What selective breeding and why is it done?

Answer 11

Selective breeding is when humans choose an organism that has a certain characteristic and then breed more of these organisms, making that chosen characteristic more and more obvious.

Plants and animals are selectively bred for:
- disease resistance (how well they cope with diseases)
- yield
- coping with certain environmental conditions
- speed of growth
- flavour

Question 12

4.8 How are plants and animals impacted by selective breeding?

Answer 12

• Animal welfare has to be considered, as selective breeding can result in medical conditions or a difficult lifestyle.
• Also, there are some issues as farming/growing huge numbers of the same breed or variety increases chance of them all dying. As all the organisms are very similar, if a change in conditions affects one organism, it affects them all.

Question 13

4.8 Evaluate the benefits (2) and risks (4) of selective breeding in modern agriculture and medicine, including practical and ethical implications

Answer 13

Advantages
+ Increases yields - desired alleles coding for desired traits
+ Used in medical research - e.g. in alcoholism research - rats have been breed to have either strong or weak preference to alcohol - allows an increased understanding in behaviour

Disadvantages
+ Reduces the gene pool - the number of different alleles in a population - may have lost useful alleles in the process.
+ May cause health problems - genetic defects
+ Takes a longer time - over many generations
+ May not show the desired characteristics

Question 14

4.9 Describe the process of (plant) tissue culture and its uses (4) in plant breeding programmes

Answer 14

1. Piece of plant placed in bleach solution
2. Few cells / small piece of plant cut of and placed on sterile nutrient medium
3. Callus - a clump of undifferentiated cells grows
4. Callus treated with hormones so plantlets develop with shoots and roots
   (Everything must be sterile to prevent growth of microorganisms)

Uses
- produce many identical plants:
- To preserve species that are rare
- To produce plants that are difficult to grow naturally - e.g. orchids
- To produce plants that all have desirable traits e.g. tasty fruit, pesticide resistant

Question 15

4.9 Describe the process of (animal) tissue culture and its uses (5) in medical research

Answer 15

Animal tissue culture is the growing of cells or tissue in a liquid containing nutrients or in a solid medium, often to produce identical cells. The cells form a callus (a clump of undifferentiated cells). Although some may be treated so they differentiate.

Uses:
- To grow tissues for transplant
- For research into tumour growth
- For research into viruses - viruses can only live inside cells
- Easier to control a dish of cells rather than a whole organism
- More ethical to research in a dish of cells than a whole organism

Question 16

4.10 Describe genetic engineering

Answer 16

A process which involves modifying the genome of an organism to introduce desirable characteristics

Question 17

4.11 Describe how genetic engineering of insulin works

Answer 17

Step 1: Using restriction enzymes “cut out” the part of the human chromosome that is responsible for producing insulin (the useful gene). This process produces sections of a few unpaired bases at each end - these are ‘sticky ends’

Step 2: Using the same restriction enzyme cut open a ring of bacterial DNA (a “plasmid”). By using the same restriction enzyme that was used on the human chromosmes, the cut plasmids have the same ‘sticky ends’.

Step 3 Sections of DNA containing the insulin gene are mixed with the cut plasmids. The complementary bases on the ‘sticky ends’ pair up and an enzyme called ligase is used to join the ends together.

Step 4: Place the plasmid into a bacterium which will start to divide rapidly and produce insulin. Commercial quantities of insulin can then be produced.

Question 18

4.11 What is ‘ligase’?

Answer 18

Ligase is an enzyme used to join the ‘sticky ends’ of strands of DNA together.

Question 19

4.11 What are ‘sticky ends’?

Answer 19

Sticky ends are sections of a few unpaired bases at each end of a DNA strand

Question 20

4.11 What is a ‘restriction enzyme ‘?

Answer 20

An enzyme that cuts DNA molecules into pieces

Question 21

4.11 What is a vector in reference to genetic engineering?

Answer 21

Any DNA molecule used to carry new DNA into another cell is called a vector

Question 22

4.12 Explain the advantages (5) and disadvantages (3) of genetic engineering to produce GM organisms

Answer 22

Advantages
+ Produce bacteria that proteins that help treat diseases - e.g. insulin
+ Produce crops that produce beta carotene - golden rice - needed for vitamin A - could improve deficiencies in developing countries
+ Produce crops that have bt toxin gene that produces an insecticide - increases yield
+ Produces crops that are drought resistant
+ Carried out once no need to repeat over generations

Disadvantages
+ Long term effects to biodiversity unknown - gene could be transferred to wild plants
+ Genetically engineered seeds are more expensive
+ Requires specialist equipment

Question 23

4.13 Explain the advantages (3) and disadvantages (6) of fertilizers as a solution to the demands of a growing human population

Answer 23

Advantages
+ Can increase the amount of food we produce
+ Fertilisers can increase crop yield and improve poor quality land.
+ They are nutrient specific

Disadvanatges:
+ Crops grow better, but so do weeds. Therefore herbicide sprays are required too.
+ Better quality plants attract insects so pesticides may be needed.
+ Excess nitrogen from fertilisers gets into water supplies, polluting it and causing fish to die. It can also affect animlas and humans who drink the water.
+ Chemicals need to be used safely. Otherwise fertilisers, pesticides and herbicides can damage peoples health.
+ They provide only short term benefits.
+ They change the nature of soil, making it either too acidic or too alkaline.

Question 24

4.13 Explain the advantages (4) and disadvantages (4) of biological as a solution to the demands of a growing human population

Answer 24

Advantages:
+ Normally whatever predator is introduced will only control the population of the pest they are meant to target, making it a green alternative to fertilizers.
+ Natural enemies introduced to the environment are capable of sustaining themselves
+ Mostly always effective
+ Can control insects and weeds

Disadvanages
+ You can’t control whatever you set loose into the ecosystem.
+ It’s a slow process
+ They can normally only reduce the number of harmful pests rather than eradicate them
+ Expensive to plan and set up

Question 25

4.14 Evaluate the benefits (5) and risks (6) of genetic engineering in modern agriculture and medicine

Answer 25

Advantages
+ Genetic modification is a faster and more efficient way of getting the same results as selective breeding.
+ Improves crop yields or crop quality, which is important in developing countries.
+ Introduce herbicide resistance, which results in less herbicides being used, as weeds are quickly and selectively killed.
+ Insect and pest resistance can be developed and inserted into the plants. The plant produces toxins, which would discourage insects from eating the crop.
+ Genetically modified insects, for example mosquitoes, could be created to combat diseases such as malaria, dengue fever and the Zika virus. For example, GM male mosquitoes released to mate with wild females could produce offspring that cannot survive adulthood.

Disadvantages
+ Genetic modification involves the transfer of the selected gene into other species. What benefits one plant may harm another. This could create ‘superweeds’ that are resistant to pesticides.
+ Some people believe it is not ethical to interfere with nature in this way.
+ GM crop seeds are often more expensive and so people in developing countries cannot afford them.
+ GM crops could be harmful, for example toxins from the crops have been detected in some people’s blood.
+ GM crops could cause allergic reactions in people.
+ Pollen produced by the plants could be toxic and harm insects that transfer it between plants