Topic 4 - Natural Selection And Genetic Modification

Question 1

Darwin’s theory of evolution

Answer 1

• Individuals in a population show genetic variation because of differences in their alleles, these differences arise from mutations.

• There is a selection pressure that affects an organism’s chance of survival (predation, competition for resources).

• Those individuals with characteristics that make them better adapted to the selection pressures in their environment are more likely to survive and reproduce.

• The advantageous allele/characteristic is passed on to their offspring. This continues and over time the mutation is more common in the population. This is survival of the fittest.

Question 2

Evidence for evolution:
Bacteria

Answer 2

• Bacteria sometimes develop random mutations in their DNA. These can create new alleles which can change the bacterias characteristics.
• One of these mutations may give them resistance to an antibiotic.
• If an organism is infected with bacteria and some of them have resistance, they are likely to survive the treatment with antibiotics.
• For bacterium, the ability to resist the antibiotic is a big advantage, a resistant bacterium is better able to survive than a non-resistant bacterium - and so it lives for longer and reproduces many more times.
• This leads to the allele for resistance being passed on to lots of offspring - it’s natural selection.

Question 3

How is bacteria evidence for evolution?

Answer 3

Antibiotic resistance provides evidence for evolution because it makes the bacteria better adapted to an environment in which antibiotics are present. And as a result, antibiotic resistance becomes more common in the population over time. The emergence of other resistant organisms also provides evidence for evolution.

Question 4

Evidence for evolution:
Fossils

Answer 4

• Generally, the deeper the rock, the older the fossil.
• Radiometric dating - by measuring the presence of a short-life radioactive element e.g. carbon-14.
• Comparing the fossil to other tools/fossils that have been dated.
• Comparing the fossil to other finds from the same layer of rock.
• By arranging fossils in chronological order, gradual changes in organisms can be observed.
This provides evidence for evolution because it shows how species have changed and developed over billions of years.

Question 5

Ardi from 4.4 million years ago

Answer 5

• The fossil was described as having a mixture of human and ape like characteristics.
• Large ape-like big toes for grasping branches suggests Ardi climbed trees.
• The leg structure indicates that Ardi walked upright.
• Long arms and short legs are more ape like.
• Ardi’s hands show that she did not use them to help her walk as apes do.
• The brain was a similar size to a chimpanzee.

Question 6

Lucy from 3.2 million years ago

Answer 6

• The fossil was also described as having a mix of human and ape like characteristics.
• Lucy us more human like than Ardi.
• The length of the arms and legs are in between an ape and a human.
• The feet have an arch and are adapted to walking rather than climbing.
• The leg structure indicates that Lucy walked upright and more efficiently than Ardi.
• The brain was a similar to size to a chimpanzee but slightly larger than Ardi’s.

Question 7

“Turkana Boy” Homo erectus from 1.6 million years ago

Answer 7

• In 1984 his team discovered a 1.6 million year old fossil of the homo erectus species.
• The fossil was named Turkana Boy after the region it was found in.
• Turkana Boy still has a mixture of human and ape like characteristics.
• The feet and leg structure show he walked upright and was better suited to this than Lucy.
• The length of the arms and legs were much more like humans than apes.
• The brain was larger than Lucy’s and similar to that of a human.

Question 8

How are stone tools made?

Answer 8

Stone tools made by hitting rock together and refining them.

Question 9

How are stone tools evidence for evolution?

Answer 9

Over time the stone tools have become more complex indicating that humans have become more intelligent which is further backed up by an increase in brain volume.

Question 10

How does a scientist work out how old stone tools are?

Answer 10

• Looking at the structural features of the tool or fossil.
• Using stratigraphy - the study of rock layers. Older rock layers are normally found below younger layers, so tools or fossils in deeper layers are usually older.
• Stone tools are usually found with carbon-containing material e.g. a wooden handle. Carbon-14 dating can be used to date this material.

Question 11

Common ancestor

Answer 11

Humpback whales and dolphins are thought to have evolved from an animal that lived about 40 million years ago, this is called a common ancestor (last common ancestor).

Question 12

Why were some classifications based on characteristics were wrong?

Answer 12

Because the characteristics were similar due to adaptation to the same environment.

Question 13

Why is genetic evidence better than evidence from observable characteristics for classification?

Answer 13

This is because DNA is not changed by the environment. Similar DNA means similar inheritance.

Question 14

Three domains:
Bacteria

Answer 14

• No nucleus
• No unused DNA

Question 15

Three domains:
Archaea

Answer 15

• No nucleus
• Unused DNA

Question 16

Eukarya

Answer 16

• Animals
• Fungi
• Plants
• Protists with cilia
• Protists with flagella
All have a nucleus.

Question 17

Explain how DNA sequencing techniques can be used to determine relationships between organisms?

Answer 17

The DNA sequences for the same gene in different organisms can be compared the more similar the DNA base sequence the more closely related the organisms are.

Question 18

Explain how genetic analysis led to the prokaryote kingdom being split into two domains?

Answer 18

Genetic analysis led to the discovery that members of the prokaryote kingdom were not as closely related as previously thought so it was suggested that the organisms in it were split into the two domains of archaea and bacteria.

Question 19

Selective breeding

Answer 19

A process where humans select desirable features within an organism and breed them over many generations until the desirable characteristic is present in greater number in the population.

Examples:
• Dogs
• Horses
• Cows
• Cabbages
• Wheat

Question 20

Selective breeding prcess

Answer 20

1. Identify organisms with desirable characteristics.
2. Cross breeding of selected individuals
3. Select the best offspring and continue to breed.
4. Repeat the process over many generations.
5. Over time, the desirable characteristics increases in appearance.

Question 21

Advantages and disadvantages of selective breeding?

Answer 21

+ Produces organisms with desirable features.
- Reduction in genetic variation.
- Vulnerable to disease.
- Organisms could have genetic defects.
- Takes place over many generations.

Question 22

When selective breeding plants, what are the desirable characteristics?

Answer 22

• Disease resistance
• Increased yield
• Coping with the environment e.g. drought
• Fast growth
• Nutrition

Question 23

Genetic engineering

Answer 23

Modifying an organisms genome (its DNA) to introduce desirable characteristics. This involves the use of enzymes and vectors (carriers).

Question 24

Enzymes involved in genetic engineering

Answer 24

• Restriction enzymes recognise specific sequences of DNA and cut the DNA at these points - the DNA are left with sticky ends where they have been cut.
• Ligaze enzymes are used to join 2 pieces of DNA together at their sticky ends.
Two different bits of DNA stuck together are known as recombinant DNA. 

Question 25

How to transfer DNA into target cells?

Answer 25

With vector DNA.
Vector DNA is often a plasmid or a virus.

Plasmid = small circular molecules of DNA that can be transferred between bacteria.
Viruses = Insert DNA into the organisms they infect.

Question 26

How genetic engineering works?

Answer 26

1) Restriction enzymes are used to isolate the required gene leaving it with sticky ends. Sticky ends are a short section of unpaired bases.
2) A bacterial plasmid is cut by the same restriction enzyme leaving it with corresponding sticky ends.
3) The plasmid and the isolated gene are joined together by ligase enzyme.
4) The plasmid inserts the gene into required cells.
5) The genes are transferred to animal, plant or microorganism cells, during early development, which allows them to develop with the desired characteristics.
6) The genetically engineered bacteria can be placed in a fermenter to reproduce quickly in controlled conditions and make large quantities of human protein.

Question 27

Genetic engineering in agriculture and medicine:
Positives

Answer 27

• Faster and more efficient way of getting the same results as selective breeding
• Improve crop yields or crop quality, (developing countries). Reducing hunger around the world.
• Introduce herbicide resistance, (less herbicides used) as weeds are quickly and selectively killed.
• Insect and pest resistance inserted into the plants (so plant produces toxins, discouraging insects from eating crop)
• Sterile insects could be created e.g mosquitos. Breeding, would lead to infertile offspring. Help slow spread of diseases, e.g malaria, dengue fever and the Zika virus.

Question 28

Genetic engineering in agriculture and medicine:
Negatives

Answer 28

• Transfer of the selected gene into other species. What benefits one plant may harm another.
• Unethical/ un­natural. GM crop seeds more expensive so people in developing countries cannot afford them
• GM crops could be harmful, e.g toxins from the crops have been detected in 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 (impact on food chains)