SB4 - Natural selection and genetic modification

What was the work of Darwin in the development of the theory of evolution by natural selection?

Darwin noticed that there was variation in members of the same species and that those with characteristics most suited to the environment were more likely to survive.

He also noticed characteristics could be passed on to offspring.

He wrote his theory of evolution by natural selection to explain his observations.

Who was Wallace and why is he significant?

Alfred Russel Wallace was a scientist working at the same time as Darwin.

He came up with the same ideas.

Darwin and Wallace published their papers on evolution together and acknowledged each other’s work.

But, it was Darwin’s famous book ‘On the Origin of Species’ that made other scientists pay attention to this theory as it provided a lot of evidence.

How have ideas about Evolution influenced modern biology?

We now understand life changes through the process of evolution, and that evidence suggest we have all descended from a common ancestor.

This has affected lots of different areas of biology, including:

CLASSIFICATION

• If all living organisms have descended from a common ancestor, then we’re all related in some way. We know classify organisms based on how closely they are related

ANTIBIOTIC RESISTANCE

• We now understand the importance of finishing the course of drugs to prevent resistant bacteria spreading and we know we need to constantly develop new antibiotics to fight newly evolved resistant bacteria

CONSERVATION

• We now understand the importance of genetic diversity and how it helps populations to adapt to changing environments. This has led to conservation projects to protect species

Ardi information.

Ardi is a fossil of the species Ardipithecus ramidus. She was found in Ethiopia and is 4.4 million years old. Ardi’s features are a mixture of those found in humans and in apes.

1. The structure of her feet suggest she climbed trees — ape like big toe to grasp branches

2. She also had long arms and short legs (more ape than human)

3. Her brain size was about the same as a chimpanzee’s

4. But the structure of her legs suggest she walked upright. Her hand bone structure also suggests she didn’t use her hands to help her walk (like apes do)

Lucy information.

Lucy was found in Ethiopia and is 3.2 million years old. Lucy also has a mixture of human and ape features, but she is more human like than Ardi.

1. Lucy has arched feet, more adapted to walking than climbing

2. The size of her arms and legs was between what you would expect to find in apes and humans

3. Her brain was slightly larger than Ardi’s but still similar in size to a chimp’s brain

4. Structure of Lucy’s leg bones and feet showed that she walked upright but more efficiently than Ardi

What were Leakey’s discovery of fossils?

In 1984, scientist Richard Leakey organised an expedition to Kenya to looked for r hominid fossils. He and his team discovered many important fossils.

• One find was Turkana Boy — a 1.6 million year old fossil skeleton of the species Homo erectus. He has a mixture of human and ape like features but more human than Lucy

• His short arms and legs are much more like a human than an ape

• His brain size was much bigger than Lucy’s — similar to a human’s brain size

How do stone tools provide evidence for human evolution?

HOMO HABILIS (2.5 - 1.5 million years ago)

• Made simple stone tools called pebble tools by hitting rocks together to make sharp flakes. these could be used to scrape meat from bones or crack bones open

HOMO ERECTUS (2 - 0.3 million years ago)

• Sculpted rocks into shapes to produce more complex tools like simple hand axes. these could be used to hunt, dig, chop, and scrape meat from bones

HOMO SAPIENS (200,000 years ago-present)

• Flint tools widely used. Pointed tools including arrowheads, fish hooks, and needles appeared around 50,000 years ago

How can stone tools be dated?

1) Looking at the STRUCTURAL FEATURES of the tool or fossil. For example, simpler tools are likely to be older than more complex tools

2) 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

3) Stone tools are sometimes found with CARBON-CONTAINING MATERIAL, for instance a wooden handle. Carbon-14 dating can be used to date this material

How does the anatomy of the pentadactyl limb provide scientists with evidence for evolution?

A pentadactyl is a limb with 5 digits.

You can see the pentadactyl limb in many species e.g. mammals, reptiles, amphibians.

In each of these species the pentadactyl limb has a similar bone structure , but usually a different function. e.g. a human pentadactyl limb and a bat pentadactyl limb.

The similarity in bone structure provides evidence that species with a pentadactyl limb have all evolved from a common ancestor (that had a pentadactyl limb). If they’d all evolved from different ancestors, it’d be highly unlikely that they’d share similar bone structure.

How has genetic analysis led to the suggestion of three domains rather than the five kingdoms classification method?

Technology has developed further and our understandings of things like biochemical processes and genetics have increased.

This led to a rethink on how organisms are classified and to the proposal of the 3 domain system of classification by Carl Woese.

Using RNA sequencing, Woese found that some members of the Prokaryote kingdom were not as closely related as first thought.

This led to the idea of 3 domains:

ARCHAEA

• Organisms in this domain look similar to bacteria but are actually quite different

BACTERIA

• This domain contains true bacteria like E. coli

EUKARYA

• This domain includes a broad range of organisms including fungi, plants, animals, and protists

Explain selective breeding and its impact on food plants and domesticated animals

Selective breeding is when humans artificially select the plants or animals that are going to breed so that the genes for particular characteristics remain in the population.

Organisms are selectively bred to develop features that are useful or attractive.

The steps for selective breeding are usually:

1. From your existing stock, select the one which have the characteristic you’re after

2. Breed them with each other

3. Select the best of the offspring and breed them together

4. Continue this process for several generations, and all the desirable traits get stronger and stronger. Eventually all the offspring will have the characteristic

What are the advantages of selective breeding?

1. Genetic variation means cattle will have better characteristics for producing meat than others. To improve meat yields, a farmer can breed cows and bulls with this characteristic. After several generations the farmer will have a very high meat yield

2. In medical research, rats have been bred with either a string preference for alcohol or a weak preference, investigating the reasons behind alcoholism. Allowed researchers to compare the differences between the two different types of rat

What are the disadvantages of selective breeding?

Traits are chosen to benefit humans, not the animal. This can lead to physical problems in the animal.

E.g. bulldogs have a short snout and therefore experience breathing problems.

Inbreeding closely related organisms can also lead to lack of variation and higher increase in genetic disease.

E.g. Cows with huge udders lead to mastitis

What is the process of tissue culture?

1. Choose a plant you want to clone based on its characteristics

2. You remove several pieces of tissue from the parent plant. Best results if tissue is taken from fast growing roots or shoot tips

3. You grow the tissue in a growth medium containing nutrients and growth hormones. This is done under aseptic conditions to prevent growth of microbes that could harm the plants

4. As the tissues produce shoots and roots they can be moved to potting compost to carry on growing

How is animal tissue culture carried out?

1. First a sample from the tissue you wanna study e.g. tissue from the pancreas, is extracted from the animal

2. The cells in sample are separated from each other, using enzymes

3. Then they are placed in a culture vessel and bathed in a growth medium containing all the nutrients they need. This allows them to grow and multiply

4. After several rounds of cell division, the cells can be split up again and placed into separate vessels to encourage further growth

5. Once the tissue culture has been grown, it can be stored for future use

What are the advantages of tissue culture in medical research and plant breeding programmes?

• Able to carry out all kinds of experiments on tissues in isolation

• Means you can look at the effects of a particular substance or environmental change on the cells of a single tissue, without complications from other processes in the whole organism

What is genetic engineering?

Genetic engineering is a process which involves modifying the genome of an organism to introduce desirable characteristics,

What are the main stages of genetic engineering?

1. The DNA you want to insert (e.g. the gene for human insulin) is cut out with a restriction enzyme. The vector DNA is then cut open using the same restriction enzyme.

2. The vector DNA and the DNA you’re inserting are left with sticky ends. They are mixed together with ligase enzymes.

3. The ligases join the pieces of DNA together to make recombinant DNA

4. The recombinant DNA (i.e. the vector containing new DNA) is inserted into other cells, e.g. bacteria

5. These cells can now use the gene you inserted to make the protein you want. E.g. bacteria containing the gene for human insulin can be grown in huge numbers in a fermenter to produce insulin for people with diabetes

How is plant modification for insect resistance carried out?

1. A plasmid is removed from a bacterium that can infect plant cells. A plasmid containing the BT toxin gene is removed from a Bacillus thuringiensis cell

2. The Bt toxin gene is inserted into the plasmid from the bacterium that infects plant cells

3. The modified plasmid containing the Bt toxin gene is placed back into a bacterium that infects plant cells

4. Cells cultured from the crop plant are infected with bacteria containing the Bt toxin gene

5. Plants grown with the Bt toxin gene in their cells are resistant to attack by some kinds of insect

What are the advantages and disadvantages of GM Bt toxin?

ADVNATAGES

• Only affect insects that chew the plant tissue, while insecticide sprays may kill a wide range of insect species

• Less insecticide used

• Increased yields

• Farmers make more profit

DISADVANTAGES

• Toxins may kill harmless insects

• Insects may develop resistance to toxin

• More expensive to produce

Why are fertilisers used? + disadvantages of them

Plants need mineral ions from rocks and soils to produce new substances.

Fertilisers contain these mineral ions (often called NPK fertilisers) to encourage plant growth.

Overuse of fertilisers leads to run off into streams, rivers, lakes.

Can cause pollution, including eutrophication.

Also cause health problems to humans and animals that drink the water.

What is biological control?

Using organisms to control pests.

Can also control weeds.

e.g. weaker ants eating cicadas in citrus trees

e.g. Chrysolina beetles eating St Johns Wort

What are the advantages and disadvantages of biological control?

ADVANTAGES

• No chemicals on products

• No residue on products acceptable for supermarkets

• Able to store for longer

DISADVANTAGES

• They interfere with food chains