NATURAL SELECTION AND GENETIC MODIFICATION

alfred wallace developed the theory of evolution by natural selection. On his travels, he had the idea that the individuals who did not have characteristics to help them survive a change in the environment would die out. he joint studies with darwin and darwin published 'on the orgin of species'. wallace continued to work accross the world to collect more evidence, one of the most important findings was on warning colouration in animals. Much more evidence over time has resulted in our current understanding.

process of speciation:

• genetic variation exists due to mutations
• alleles which provide a survival advantage are selected for by natural selection
• species move into new environments and alleles that are advantageous are chosen, those that arent die
• overtime, selection of different alleles will increase genetic variation between 2 populations 
• when indidviduals can no longer breed together to produce fertile offspring a new species is formed.

darwin proposed the theory of natural selection:-shows how a species has evolved

• individual organisms within a particular species showa wide range of variation for a characteristic
• individuals with characteristics most suited to the environment are more likely to survive and to breed successfully (survival of the fittest)
• the characteristics that have enabled these individuals to survive are then passed on to the next generation

Bacteria are labelled resistant when they are not killed by antibiotics which previously were used as cures against them.

• Bacteria reproduce at a fast rate. Mutations during reproduction can result in the gene for antibiotic resistance. This the creation of a new strain.
• Exposure to antibiotics creates a selection pressure, as those with antibiotic resistant genes survive and those without die.
• As a result those with antibiotic resistance can reproduce and pass on the advantageous gene to their offspring. Therefore, the presence of these new, resistant bacteria supports Darwin’s theory of natural selection (as the new bacteria have been selected by the environment to have a feature (resistance) advantageous to survival.)
• This population of antibiotic resistant bacteria increases.
• Bacterial diseases spreads rapidly because people are not immune to these new resistant bacteria and there is no treatment for it.

An example is MRSA.

• Called a ‘superbug’ as it is resistant to many different types of antibiotics
• Common in hospitals: spreads when doctors and nurses move to different patients

Fossil evidence shows the developments over time of organisms, This is because we can use carbon dating/techniques to estimate when a fossil was formed, giving us a more complete picture of how an organism or species developed over time. Examples of these:

ARDI: Ardi is a female human/ape-like fossilised skeleton that dates from 4.4 million years ago. Ardi's bones show that she was probably able to walk upright but she had very long arms and long big toes. The bones that make up Ardi's feet suggest that humans and chimpanzees evolved separately.

LUCY: Lucy is also a female human-like fossilised skeleton, and dates from 3.2 million years ago. Lucy's bones suggest that she walked in an upright position, like a human, but possessed a relatively small ape-like skull. Lucy's foot bones show that she had similar feet to modern humans but with much more curved toes.

LEAKEYS' DISCOVERIES: Fossils discovered by archaeologists Louis and Mary Leakey in the 1950s helped support the theory of natural selection, especially an early fossil which contained remnants of stone tools (thought to be an early toolmaker), The skeleton looks much more like that of a modern human than either Ardi or Lucy. This most recent skeleton suggests that humans may have evolved. 

We can use stone tools found as part of archaeological digs as evidence for human evolution. It is clear how stone tools have become more complex as our brains evolved in complexity:

Early Stone Age tools - Homo habilis (1.5 million years ago)

• Used basic pebble tools (‘Oldowan tools’) created by smashing rocks together.
• These tools had simple uses, such as cracking nuts.

Late Stone Age tools - Homo neanderthalensis (40,000 years ago) and modern Homo sapiens:

• These more advanced species used pointed arrowheads, spears and hooks
• This enabled more advanced tasks to be carried out, such as catching fish.

We can date these tools using two main methods:

1. Radiometric carbon dating - by looking at the natural radioactive decay of an isotope of Carbon (Carbon-14) we can estimate how long ago an organism lived. If any once-living material is found with a tool, such as a piece of wood or fur, we can date this to find the age of the rock.
2. Stratifying rock layers - looking at the layer of sediment in which a rock was found is a useful tool for archaeologists. Each layer of sediment, and everything within it, must have been formed at the same time. Therefore, we can date once-living fossils in this layer and use this to estimate when the tools were formed.  

A pentadactyl limb is a limb with five digits. This can be seen in a number of organisms, implying that they all come from a common ancestor - and that each ‘branched off’ at some stage of evolution. This could have been due to different selection pressures within different environments.

The human hand has five digits (four fingers and a thumb), but bats, cats, horses and birds also have this pattern within their limbs. However, that does not mean that we evolved directly from these animals but humans are distantly related to them via a common ancestor.  

Five Kingdoms system:

• Animals
• Plants
• Fungi
• Prokaryotes (e.g bacteria)
• Protists (e.g algae, amoebas and other single-celled eukaryotic organisms)

Each kingdom is then subdivided into a phylum, class, genus, order and species. These are different for each organism. EG a human would be of the Animal kingdom, its phylum is Chordata, class is Mammalia and Order is Primate. The binomial naming system is based on the genus and species; for example, Homo sapiens is of the genus Homo, which also contains Homo habilis and Homo erectus, to name a few.  

Developments in science such as the improvement of the microscope and increased knowledge of biochemistry (for example, RNA sequence analysis) found that some species were more distantly related than first thought

Carl Woese added three large groups called domains above kingdoms

• Archaea: primitive bacteria which live in extreme environments such as hot springs
• Bacteria: true bacteria (despite having similar features to archaea)
• Eukaryota: organisms who have a nucleus enclosed in membranes, includes the kingdoms protists, fungi, plants and animals  

Selective breeding is when humans choose which organisms to breed in order to produce offspring with a certain desirable characteristic (e.g animals with more meat, plants with disease resistance or big flowers).

This has been happening for many years since animals were domesticated and plants were grown for food.

• Parents with desired characteristics are chosen.
• They are bred together.
• From the offspring those with desired characteristics are bred together.
• The process is repeated many times until all the offspring have the desired characteristic.

The problem is that it can lead to inbreeding.

• Breeding those with similar desirable characteristics means it is likely you are breeding closely related individuals.
• This results in the reduction of the gene pool, as the number of different alleles reduce (as they mostly have the same alleles).
• This means if the environment changes or there is a new disease, the species could become extinct as they all have the same genetic make-up (so the chance of a few organisms having a survival advantage and not dying is reduced). This is particularly relevant in selective breeding of plants, as one disease could spread rapidly and destroy the entire population of crops. This could cause severe economic problems, especially for the farmers who rely on income from their crops.
• Another problem is that the small gene pool leads to a greater chance of genetic defects being present in offspring, as recessive characteristics are more likely to present. This is particularly relevant in domesticated animals, which have a much higher frequency of genetic conditions than normal.  

Tissue culture is a method of culturing living tissue, making it grow outside the organism, within a growth medium. This is especially useful for plants - we can produce an entire field of identical cloned crops using just a small cutting. Tissue culture can also be used to culture animal and human tissues outside of the body. 

In plants, this is performed as follows:

1. Take the plant that you would like to clone - for example, a plant with desirable characteristics.
2. Using tweezers, remove a piece of tissue from a fast-growing region of the plant, e.g the root or shoot tip.
3. Using aseptic technique (maintaining sterile conditions), place the tissue on a special growth medium (containing hormones and nutrients).
4. Once the tissue has developed enough (e.g produced shoots and roots), it can be transferred to compost for further growth.  

benefits:

• produces lots of offspring with desirable characteristics
• Increasing the number of crops resistant to bad weather, for example, can increase crop yields
• Can help extremely endangered species, or even bring back species that have become extinct. 

risks:

• The gene pool is reduced through producing clones, meaning it is less likely that the population will survive if a disease arises with low diversity in the population
• Clones have a low survival rate, and tend to have some genetic problems
• It may lead to human cloning. 

Genetic engineering: Modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic.

• Plant cells have been engineered for disease resistance or to have larger fruits
• Bacterial cells have been engineered to produce substances useful to humans, such as human insulin to treat diabetes.  

genetic engineering: 

1. Genes from chromosomes are ‘cut out’ using restriction enzymes.

2. The same restriction enzymes are used to cut the vector (such as a virus or bacterial plasmid) into which the genes will be placed.

3. Ligase enzyme is used to attach the sticky ends of the gene and the vector together, to produce a recombinant gene product.The vector is placed in another organism at an early stage in development so the desired gene moves into its cells and cause the organism to grow with the desired characteristics. In plants the vector is put into meristematic cells (unspecialised cells) which can then produce identical copies of the modified plant.  

Genetically modified crops

• They are engineered to be resistant to insects and to herbicides.
• This will result in increased yields as less crops will die.

Genetic modification in medicine

• It may be possible to use genetic engineering to cure inherited disorders.
• It is called gene therapy and involves transferring normal genes (not faulty) into patients so the correct proteins are produced.  

benefits:

• It can be very useful in medicine to mass produce certain hormones in microorganisms (bacteria and fungi).
• In agriculture it can be used to improve yields by:
  • Improving growth rates
  • Introducing modifications that allow the crops to grow in different conditions, e.g. hotter or drier climates
  • Introducing modifications that allow plants to make their own pesticide or herbicide 
• Crops with extra vitamins can be produced in areas where they are difficult to obtain.
• Greater yields can help solve world hunger, which is becoming an increasingly bigger issue due to population growth.  

risks:

• GM crops might have an effect on wild flowers and therefore insects.
  • GM crops are infertile and these genes could spread into wild plants, leading to infertility in other species, which affects the entire environment.
  • Growing with herbicides and pesticides can kill insects and other plants, which would reduce biodiversity. 
• People are worried that we do not completely understand the effects of GM crops on human health.
• Genetic engineering in agriculture could lead to genetic engineering in humans. This may result in people using the technology to have designer babies.
• They pose a selection pressure, which could lead to increased resistance in other species, creating super weeds and pests.  

Bt crops

Bacillus thuringiensis is the name of a bacteria that produces toxins that kill insect larvae. This is a useful function for crops, so we use genes from the bacteria in crops to increase their insect resistance. Genes are cut out from the bacteria using restriction enzymes, and re-inserted into the crop using ligase, as described above. The crop will then produce the toxin - any insects that eat the crop will die. As a result, less of the crop gets eaten by insects, increasing the crop yield and profits. However, there are concerns over this method - we don’t know if the toxin has any effect on human health, for example. Killing insects also results in a loss of biodiversity, which can affect the entire ecosystem. 

We can use various agricultural solutions to cope with the demands of a growing human population. Two of the most useful methods are:

1) Fertilisers - fertilisers provide useful nutrients (nitrates and phosphates) to plants, making them more resistant to environmental conditions and able to grow faster and larger - resulting in increased crop yields. However, excess fertiliser can often run off into rivers, killing fish and other wildlife and affecting biodiversity.

2) Biological control - biological control is the use of certain species to control population of other species. For example, Aphelinus abdominalis, the aphid killer wasp, has been used successfully to control aphid populations - which feed on fruit crops. However, this reduces biodiversity, and again, has a knock-on effect across the whole ecosystem.  

benefits:

• It is possible to greatly increase the yield of a particular crop by selectively breeding only individuals that produce higher quality or a larger mass of food.
• Individual plants or animals can be bred to be resistant to a particular disease, which could increase crop yield

risks:

• Selecting for advantageous characteristics can sometimes cause severe health problems in the offspring - e.g chickens that have been bred to have more meat (muscle) are sometimes too large to be able to walk.
• Lack of genetic variation - Despite the bred population being able to have resistance to a particular disease (or multiple diseases), if one of them has susceptibility to a different disease then they all do - and the entire population could be wiped out as a result.
• There are ethical issues associated with selective breeding -many people consider it unethical to selectively breed for characteristics wanted by humans if it means that the offspring will suffer, or have a reduced quality of life as a result.  

benefits:

• It can be very useful in medicine to mass produce certain hormones in microorganisms (bacteria and fungi).
• In agriculture it can be used to improve yields by:
  • Improving growth rates
  • Introducing modifications that allow the crops to grow in different conditions, e.g. hotter or drier climates
  • Introducing modifications that allow plants to make their own pesticide or herbicide
• Crops with extra vitamins can be produced in areas where they are difficult to obtain.
• Greater yields can help solve world hunger, which is becoming an increasingly bigger issue due to population growth.  

risks:

• GM crops might have an effect on wild flowers and therefore insects.
  • GM crops are infertile and these genes could spread into wild plants, leading to infertility in other species, which affects the entire environment.
  • Growing with herbicides and pesticides can kill insects and other plants, which would reduce biodiversity.
• People are worried that we do not completely understand the effects of GM crops on human health.
• Genetic engineering in agriculture could lead to genetic engineering in humans. This may result in people using the technology to have designer babies.
• They pose a selection pressure, which could lead to increased resistance in other species, creating super weeds and pests.  

b