Biology- B4: Natural Selection and Genetic Modification

What is evolution?

-A gradual change in the inherited traits within a population over time.

-Occurs due to natural selection.

Outline the theory of natural selection.

1) Genetic variation exists due to spontaneous mutations.

2) Selection pressures (e.g. competition, disease) exist.

3) Random mutation gives an organism a selective advantage.

4) Organism is better adapted to the environment and survives.

5) Organism reproduces, passing on its beneficial alleles.

6) Frequency of advantageous alleles increase.

Why does competition between organisms in a habitat exist?

The resources within a habitat required for survival are limited.

Give some examples of competition between organisms within a habitat.

Competition between animals for food, shelter, mates etc.

Competition between plants for light, water minerals etc.

Describe how antibiotic resistance in bacteria can be used as an example to illustrate the process of evolution?

1) Genetic variation exists due to spontaneous mutations.

2) Antibiotics act as a selection pressure.

3) Mutations gives a bacterium antibiotic-resistance.

4) If an antibiotic is administered, the bacterium is better adapted and survives, whilst other bacteria are killed.

5) Bacterium reproduces, passing on its resistant variant.

6) Frequency of antibiotic-resistant allele increases.

Why is the development of antibiotic resistance in bacteria a good study for evolution?

Bacteria reproduce very rapidly, allowing the first-hand observation of evolution.

How can the observation of fossils provide evidence for evolution?

-Older fossils (found in rocks deeper in the ground) contain simpler organisms. Newer fossils (found closer to the surface) contain more complex organisms. Comparisons of fossils show that simple organisms evolved into more complex life forms.

-Fossils can be organised into chronological order, allowing the changes in organisms over time to be observed.

Describe the role of Darwin in the development of the theory of evolution by natural selection.

-Studied a variety of organisms whilst travelling around the world on the HMS beagle.

-Noted that traits can be passed from parents to offspring.

-Proposed the idea of ‘survival of the fittest’.

-Established the theory of natural selection and published his ideas in ‘On the Origin of Species’.

Describe the role of Wallace in the development of the theory of evolution by natural selection.

-He proposed a theory of natural selection that was similar to Darwin’s, although the mechanisms were different.

-He gathered greater evidence (e.g. studying warning colouration in butterflies) to support the theory.

How has the theory of evolution by natural selection impacted modern biology and society?

-Enables the classification of organisms into taxa.

-Influences modern medicine by emphasising the importance of finishing antibiotic treatments and the need for constant production of new antibiotics.

-Highlights the importance of high genetic diversity in habitats which aids conservation projects.

What fossils have provided evidence for human evolution?

-’Ardi’ - 4.4 million years old.

-’Lucy’ - 3.2 million years old.

-Leakey discovered 1.6 million year old fossils.

What clues does ‘Ardi’ give scientists about human evolution?

Female hominid fossil. She shows phenotype traits which encompass characteristics of both humans and apes:

-Ape-like characteristics e.g. long arms, large big toes.

-Human-like characteristics e.g. the structure of her bones suggests that she walked upright.

What clues does ‘Lucy’ give scientists about human evolution?

Female hominid fossil. She shows phenotype traits which are more human-like than that of ‘Ardi’:

-The structure of bones in her legs and feet are more adapted to walking than climbing.

-However, her brain size is closer to that of an ape’s.

How does Leakey’s findings provide evidence for human evolution?

He discovered many hominid fossils.

The 1.6 million year old fossil ‘Turkana Boy’ showed traits comparable to that of modern-day humans e.g. similar brain size.

How has the development of stone tools provided evidence for evolution?

-Correlation between the development of more complex tools and an increase in brain size.

-Primitive tools are older than more complex tools. Brain size has increased over time therefore as brain size increased, advancements in tool use were made.

Describe the methods used by scientists to date tools.

-Carbon-14 dating- estimating the age of carbon-containing material that is found in tools (e.g. wooden handles) or alongside tools (e.g. fur).

-Stratigraphy- using the age of the layers of sediment surrounding the tool as an indication of the age of the tool.

What is a pentadactyl limb?

A limb with five digits present in animals, bird, reptiles and amphibians.

How does the pentadactyl limb provide evidence for evolution?

The presence of the pentadactyl limb suggests that all species which possess it have descended from a common ancestor.

What is classification?

The organisation of organisms into groups.

What is taxonomy?

The classification of organisms into taxa: kingdom, phylum, class, order, family, genus, species.

Name the five kingdoms.

Animals, plants, fungi, protists, prokaryotes.

What happens to the number of organisms in each taxon as you move down the hierarchy?

The number of organisms in each taxon group decreases.

Traditionally, organisms were grouped based on similarities and differences in their anatomy and behaviour. What is the problem with this?

-Organisms that are not closely related may look alike and behave similarly if they live in the same environment e.g. sharks and dolphins.

-Some closely related species may look very different if they live in different habitats e.g. queen ants, worker ants.

What advancements in science have led scientists to reconsider the five kingdoms classification system?

-Microscopes.

-Biochemistry.

-DNA and RNA analysis.

Describe the three domains system of classification.

-Organisms are initially divided into an extra three groups: Archaea, Bacteria, Eukarya.

-domain, kingdom, phylum, class, order, family, genus, species.

Which domain do eukaryotic organisms belong to?

Eukarya.

Which domains do prokaryotic organisms belong to?

Archaea and Bacteria.

Describe the domain Bacteria.

Consists of true bacteria e.g. E.coli.

Describe the domain Archaea.

-Consists of primitive microorganisms.

-Contains extremophiles- adapted to live in extreme conditions e.g. hot springs.

What is selective breeding?

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

Outline the main steps involved in selective breeding.

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.

What is the main advantage of selective breeding?

Created organisms with desirable features:

-Crops produce a higher yield of grain.

-Cows produce a greater supply of milk.

-Plants produce larger fruit.

-Domesticated animals.

Other than in agriculture, where else is selective breeding useful?

-In medical research.

-In sports e.g. horse racing.

Outline the disadvantages of selective breeding.

-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.

How can plants be cloned?

-Taking plan cuttings.

-Tissue culture.

What is tissue culture?

A method of growing living tissue in a suitable medium.

Describe how plants are grown using tissue culture.

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.

What must be ensured when preparing tissue cultures?

Ensure aseptic conditions to prevent contamination by microorganisms.

What does the growth medium contain?

Nutrients and growth hormones.

What are the advantages of growing plants by tissue culture?

-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.

What are the disadvantages of growing plants by tissue culture?

-Reduction in the gene pool.

-Plant clones often have a low survival rate.

-Could unknowingly increase the presence of harmful recessive alleles.

Why is animal tissue culturing useful?

-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.

Describe how animal tissue cultures are prepared.

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.

What is genetic engineering?

-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.

Describe the process of genetic engineering.

1) DNA is cut at specific base sequences by restriction enzymes to create sticky ends.

2) Vector DNA cut using the same restriction enzymes to create complementary sticky ends.

3) Ligase enzymes join the sticky ends of the DNA and vector DNA forming recombinant DNA.

4) Recombinant DNA mixed with and ‘taken up’ by target cells.

What is a vector?

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

Describe the benefits of genetic engineering.

-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).

Describe the risks of genetic engineering.

-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.

What is Bacillus thuringiensis (Bt)?

-Insect larvae are harmful to crops.

-Bt is a bacterium which secretes a toxin that kills insect larvae.

How is genetic engineering used to protect crops against insects?

-The gene for toxin production in Bt can be isolated and inserted into the DNA of crops.

-Bt crops now secrete the toxin which kills any insect larvae that feed on it.

What are the benefits of Bt crops?

-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.

What are the risks of Bt crops?

-Long term effects of consumption of Bt crops unknown.

-Insect larvae may become resistant to the Bt toxin.

-Killing insect larvae reduces biodiversity.

Outline the agriculture methods of increasing food production.

-Intensive farming methods e.g. ‘battery’ farming and the use of fertilisers and pesticides.

-Biological control.

What is the main advantage of intensive farming?

Increases crop yields.

What are the disadvantages of intensive farming methods?

-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.

What is biological control?

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

What are the advantages of using biological control to increase food production?

-The results of biological control generally last for a long period of time.

-The effects of wildlife are less severe.

What is the risk of using biological control?

Risk of the control organism becoming a pest itself.