Natural Selection and Genetic Modification - Topic 4

• Evolution = a gradual change in the characteritics of a species over a long period of time
• Species = a group of organisms that can reproduce with each other to produce offspring that will also be able to reproduce
• Bionomial system is the system of naming species proposed by Carl Linnaeus.
• Each species is named using 2 Latin words, the first is the genus and the second the species. 

A. Fossil evidence

• A fossil is the preserved remains of an organism that lived long ago. Fossils found in the lower levels of rocks were formed first and are therefore the oldest.
• Scientists have studied skulls to try and understand the evolution of humans. Over time the size of the skull has increased to house a larger brain
• Gaps occur in the fossil evidence and that means that scientists cannot be certain that species evolved into one another
• Significant fossil finds: Ardi, Luci, Homo habilis and Homo erectus

B. Stone tools

• The earliest evidence for use of stone tools dates back 3.3 million years ago. The age of stone tools is obtained by knowing the age of the rock in which they are found
• Tools were used to:

- cut meat and grind seeds

- scrape animal skins

- spears or arrow heads for hunting

• Over time the tools have developed for example more work went into more complex tools and there is a wider range of different tools for different tasks were made.

• Increase in skull volume and therefore brain size
• Became taller with increasing ability to walk upright

• Charles Darwin and Alfred Russel Wallace published ideas on how organisms evolved into others
• Natural selection = process in which certain organisms are more likely to survive and reproduce than other members of the same species, because they process certain genetic variations

• Genetic variation - characteristics of individuals vary
• Environmental change - this will result in comepetition between individuals e.g. for food
• Natural selection - some individuals cope better with the change and are more likely to survive (survival of the fittest)
• Inheritance - survivors breed to pass their variations on to their offspring (these offspring are better adapted to the changed environment)
• Evolution - if the environment conditions remain changed, natural selection continues until a new species evolves

• Common ancestor - organism from which more recent organisms descended

A. Pesticide Resistance in Rats

• Warfarin was used to poison rats. Those that survived bred to produce offspring that were resistant to warfarin.

B. Antibiotic Resistance

• Certain bacteria e.g. MRSA are now resistant to many antibiotics
• This is caused by the overuse of antibiotics and not completing a course of antibiotics.

• Bacteria in a population show variation in the amount of resistance to an antibiotic
• A course of antibiotics is started
• With time, the antibiotic kills more and more of the bacteria. The most resistant bacteria take the longest to die
• A course of antibiotics is finished to early
• The resistant bacteria survive and reproduce. The new population of bacteria are all now resistant to the antibiotic.

• Living organiama can be classified into 5 kingdoms based on what their cells look like
• Animals - multicellular, cells have nuclei, no cell walls
• Plants - multicellular, chlorplasts for photosynethesis, cells with nuclei, cell walls of cellulose
• Fungi - multicellular, live in/on dead matter which they feed on, cells have nuclei, cell walls of chitin
• Protists - mostly unicellular, cells have nuclei
• Prokaryotes - unicellular, cells DO NOT have nuclei, flexible cell walls

• The new bacteria (archaea) was discovered allowing scientists to improve genetic analysis and classify organisms more accurately.
• They have discovered that all organisms except for prokaryotes have unused sections of DNA in their genes. These unused sections do not code for proteins.

• Archaea - cells with no nucleus, genes contain unused sections of DNA
• Bacteria - cells with no nucleus, no unused sections of DNA
• Eukarya - cells with a nucelus, unused sections in genes

• Scientists can use DNA to work out how closely related two organisms are.
• The more DNA two organisms have in common, the more recently evolved from a common ancestor and the more closely related they are.

• Artificial selection - when humans choose organisms with certain desirable characteristics and use these animals to breed from
• Breeding animals in this way is also called selective breeding
• Selective breeding leads to new breeds of animal species and new variations of plant species.

• Select two organisms with the desirable characteristics
• Allow them to breed
• Select the offspring with the desirable characteristics and breed them together
• Breed the organisms over many generations until all offspring have the desired characteristics

E.g.

• Domestic sheep have been bred from mouflon
• Modern wheat with more grains and shorter stems from wild wheat
• Broccoli, cauliflower, cabbage and kale from wild cabbage

• Disease resistance
• Increased yield
• Coping with certain environmental conditions
• Fast growth - greater profit in a short period of time
• Flavour

• Loss of useful alleles - during selective breeding only certain alleles are selected. Other alleles that might be useful in the future become rare or could disappear
• Genetically similar individuals will all be susceptible to a particular disease or to a change in the environment
• Animal welfare e.g. chickens bred to have large breasts struggle to stand up.

• Tissue culture - growing of cells or tissiues in a lab. Cells can be grown in a liquid containing nutrients or on a solid medium (e.g. agar)
• This gives rise to identical cells which may form a callus (a clump of undifferentiated cells)
• These cells can be treated to make them differentiate

• Produce new plants of very rare species which are at risk of extinction
• Produce offspring of plants which are difficult to grow from seeds e.g. orchids
• Used to produce clones of GM plants

• Study how cells communicate with each other
• Cell structures are used to study viruses which cannot replicate outside of cells
• Study how cancers develop and spread
• Investigate how cells respond to new medicines (avoiding harming animals and humans)
• Produce artificial body parts e.g. trachea covered with patients stem cells to prevent rejection and producing artificial bladers

• Production of many plants from a small piece of plant tissue.
• The entire procedure must be completed under sterile conditions to ensure that microorganisms do not grow

• A group of plant cells are placed on a sterile nutrient medium
• Cells form a callus
• Treatment with hormones stimulate growth of roots and shoots
• Plantlets are separated and grown on strelile nutrient mediums
• When large enough they are transferred to compost

• Genetic engineering = altering the genome of an organism, usually by adding genes from another species
• This creates genetically modified organisms (GMO's)

Uses of GMO's

• Allow plants to produce additional vitamins e.g. golden rice
• Introduce disease resistance
• Increase rate of growth e.g. AquAdvantage Salmon
• Goats and sheep can produce proteins used to treat human diseases
• In the future - GM pigs could produce human-like organs for transplants

• Golden rice is a GMO with 2 genes inserted into its genome
• This allows the rice to produce beta-carotene in its grains to make vitamin A - helps with vitiman A defficiency
• AquAdvantage salmon are Atlantic salmon with a growth hormone gene from chinook salmon, to accelerate growth, and a fragment of DNA from ocean pout, to help activate the chinook gene - increased yield 

• Seeds of GM plants are very expensive
• People are concerned that herbicide resistance may be passed from crops to wild plants
• Introduced genes may have unknown effects on wild plants
• Eating GM plants are perceived as being bad for health (no evidence)

• GM crops can be resistant to some to some insects i.e. less insecticide is required
• Other GM crops are resistant to herbicides (weed killers). The herbicides used will kill weeds, but not the crop. These herbicides do not harm animals and are very effective i.e. less herbicide is required

• To genetically engineer bacteria additional genes are added to a plasmid. This gives rise to recombinant DNA (made by joining two sections of DNA)
• The plasmid acts as a vector (DNA molecule used to carry new DNA into another cell)
• Restriction enzymes are used to cut DNA from a gene. This cutting leaves jagged ends, called sticky ends.
• The sticky ends consist of a few unpaired bases
• The same restriction enzyme is also used to cut open a plasmid to produce sticky ends complimentry to the ones on the gene to be inserted.
• Matching sticky ends can be joined together using another enzyme called ligase

• A section of DNA containing the insulin gene is cut from a human chromosome using a restriction enzyme
• The same restriction enzyme cuts open a plasmid giving rise to the same sticky ends
• The insulin gene is mixed with cut plasmids
• Complementary base pairs on sticky ends pair up and ends join using the enzyme ligase
• The plasmid (recominant DNA) is inserted back into a bacterium. The bacterium produces human insulin

• Fewer caterpillars on the crop
• Higher yield, therefore the farmer earns more money
• Need not spray the crop with as much insecticide therefore it is cheaper to grow crops
• GM crops only kill pests that eat it

• If insects develop resistance to Bt toxin, they will not be killed by eating a GM crop variety
• Still have to spray insecticide on crops to kill sap sucking insects e.g. aphids (do not eat the crop so are not killed)
• Seed for GM crop varieties much more expensive than for non-GM varieties
• Fewer caterpillars for insect eating birds
• If you have to spray instecticide to kill aphids this may kill useful insects e.g. bees (pollinators)
• New genes for insect resistance may be transferred to wild plants during pollination

Methods to increase food production and yield:

• GM organisms
• Selective breeding
• Biological control
• Fertilisers

• Biological control = using organisms to kill problem organisms, such as pests or weeds
• e.g. parasitic wasps lay eggs in caterpillars to kill them
• e.g. chrysolina beetles are introdiced to eat weeds
• Insects used for biological control need to be selected carefully so that they do not upset the natural ecosystem

• Fertilisers contain minerals that plants need for growth e.g. nitrogen, potassium adnd phosphorous.
• These are absorbed by the roots of plants from the soil as ions e.g. nitrates and phosphates
• Fertilisers need to be applied in correct amounts and at the right time to maximise uptake by plant roots.
• Heavy rain after applying fertilisers to a field can result in minerals being washed into rivers and lakes.
• This causes a type of pollution called eutrophication, which can lead to the death of acuatic organisms