Natural Selection and Genetic Modification

• Natural Selection - Survival of Fittest

  Individuals in a population show genetic variation because of differences in their alleles. New alleles arise through mutations.

  
  

  2) Thinge like predation, competition for resources (e.g. food, water, mates, sto.) and disease act as selection pressures. This means they affect an organism's chance of surviving and reproducing

  
  

  3) Those individuals with characteristics that make them better edupted to the selection pressures in their environment have a better chance of suntval and so are more likely to breed successfully.

  
  

  4) This means the alleles that are responsible for the useful characteristics are more likely to be passed on to the next generation-

  
  

  5) However, some individuals will be less wall adapted to the selection pressures in their environment and may be less able to compete. These Individuals are less likely to survive and reproduce.

  
  

  6) The beneficial characteristics become more common in the population over

  
• Bacteria Evolution


  1) Like all organisms, bacteris sometimes develop random mutations in their DNA. These can creste new alleles, which can change the bacteria's characteristics-e.g. a bacterium could become less affected by a particular antibiotic (a drug designed to kill bacteria or prevent them from reproducing).

  
  

  2) For the bacterium, the ability to resist this antibiotic is a big advantage. In a host who's being treated to get rid of the infection, a resistant bacterium is better able to survive than a non-resistant bacterium and so it lives for longer and reproduces many more times.

  
  

  3) This leads to the allele for antibiotic resistance being passed on to lots of offspring-it's just natural selection. This is how it spreads and becomes mare common in a population of bacteria over time

  
  

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

  
• Fossils Evolution


  1) A fossil is any trace of an animal or plant that lived a long time ago (e.g. over a thousand years). They are most commonly found in rocks. Generally, the deeper the rock, the older the fossil.

  
  

  2) By arranging fossils in chronological (date) 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

  
• Charles Darwin


  1) Charles Darwin was the guy that came up with the theory of evolution by natural selection.

  
  

  2) He spent 5 years on a younge around the world studying plants and animals on a ship called HMB Beagle.

  
  

  3) He 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.

  
  

  4) He also noticed that characteristics could be passed on to offspring.

  
  

  5) He wrote his theory of evolution by natural selection to explain his observations.
• Wallace


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

  
  

  2) He also came up with the idea of natural selection, independently of Darwin.

  
  

  3) He and Darwin published their papers on evolution together and acknowledged each other's work- although they didn't always agree on the mechanisms involved in natural selection.

  
  

  4) Wallace's observations provided lots of evidence to help support the theory of evolution by natural selection. E.g. he realised that warning colours are used by some species (e.g. butterflies) to deter predators from eating them an example of a beneficial characteristic that had evolved by natural selection.

  
  

  5) But it was Darwin's famous book 'On the Origin of Species' (published in 1859) that made other scientists pay attention to the theory. In this book Darwin gave lots of evidence to support the theor and expanded on it. This book is partly why Darwin is usually better remembered than Wallace.
• Evolution and Modern Biology

  1) The theory of evolution by netural selection is still relevant today it helps us to understand many areas of biology.

  
  

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

  
  

  3) This has affected lots of different areas of biology
• Classification


  classification if all living organisms have descended from a common ancestor, then we're all related in some way. We now classify organisms (arrange them into groups) based on how closely related they are
• Antibiotic Resistance


  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


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


  1) Evidence from fossils suggests that humans and chimpanzees evolved from a common ancestor that existed around 6 million years ago.

  
  

  2) Human beings and their ancestors are known as hominide. Fossils of several different hominid species have been found.

  
  

  3) These fossils have characteristics that are between apes and humans by looking at hominid fossils you can see how humans have evolved over time.
• Ardi


  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 suggests she climbed trees she had an ape-like big toe to grasp branches.

  
  

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

  
  

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

  
  

  Brain size is found by working out cranial capacity the space taken up by the brain in the skull

  
  

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

  
• Lucy


  Lucy is a fossil of the species Australopithecus afarensis. She 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 had arched feet, more adapted to walking than climbing, and no ape-like big toe.

  
  

  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) The structure of Lucy's leg bones and feet suggest she walked upright, but more efficiently than Ardi.

  
• Leakey


  In 1984 scientist Richard Leakey organised an expedition to Kenya to look for hominid fossils. He and his team discovered many important fossils of different Australopithecus and Homo species.

  
  

  1) One of their finds was Turkana Boya 1.6 million year old fossil skeleton of the species Homo erectus. He has a mixture of human and ape-like features, but is more human-like than Lucy.

  
  

  2) His short arms and long legs are much more like a human than an ape, and his brain size was

  
  

  much larger than Lucy's similar to human brain size.

  
  

  3) The structure of his legs and feet suggest he was even better adapted to walking upright than Lucy.

  
• Timeline of Evolution


  So you know that the Ardipithecus and Australopithecus species were more ape-like, compared to the Homo species, which are human-like. They can all be put on a time line, showing how humans have evolved:

  
• Development of Stone Tools

  Homo habilis - (125-15 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 - (12-0.3 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

  
  

  Homa neanderthalensis - (300 000-25000 years ago)

  More complex tools. Evidence of flint tools, pointed tools and wooden spears.

  
  

  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.

  
  

  
  

  There are several different ways scientists can work out how old it is. These include:

  
  

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

  
  

  2) Using stratigraphy the study of rook layers. Older rock layers are normally found below younger layers, so tools or fossils in deeper layers are usually older.

  
  

  3) Stone tools are often found with carbon-containing material, e.g. a wooden handle. Carbon-14 dating can be used to date this material.

  
• Pentadyctyl Limb


  1) A pentadactyl limb is a limb with five digits.

  
  

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

  
  

  3) In each of these species the pentadactyl limb has a similar bone structure, but usually a different function. For example, a human's hand and a bat's wing are both pentadactyl limbs and they look pretty alike...

  
  

  4) 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 a similar bone structure.

  
• Classification


  1) Traditionally, organisms were classified according to similarities and differences in their observable characteristics. i.e. things you can see (like how many legs something has). As technology improved, this included things you can see with a microscope, e.g. cell structure.

  
  

  2) These characteristics were used to classify organisms in the five kingdom classification system. In this system, living things are first divided into five groups called kingdoms. These are:

  
  

  Animals - fish, mammals, reptiles, etc.

  
  

  Plants - grasses, trees, etc.

  
  

  Fungi - mushrooms and toadstools, yeasts,

  
  

  Prokaryotes - all single-celled organisms without a nucleus.

  
  

  Protists - eukaryotic single-celled organisms, e.g. algae.

  
  

  3) The kingdoms are then subdivided into smaller and smaller groups that have common features phylum, class, order, family, genus, species.
• Classification Systems Changing


  6) The three domains are then subdivided into smaller groups used in the five kingdom system (beginning with kingdom and finishing with species).1) The five kingdom classification system is still used, but it's now a bit out of date.

  
  

  2) Over time, technology has developed further and our understanding of things like biochemical processes and genetics has increased. For example, we are now able to determine the sequence of DNA bases in different organisms' genes and compare them the more similar the sequence of a gene, the more closely related the organisms. Scientists are also able to compare RNA sequences in a similar way.

  
  

  3) This led to a bit of a rethink about the way organisms are classified and to the proposal of the three domain system of classification by a scientist called Carl Woese.

  
  

  4) Using RNA sequencing, Woese found that some members of the Prokaryote kingdom were not as closely related as first thought. He proposed that this kingdom should be split into two groups called Archaea and Bacteria.

  
  

  5) In fact, Woese suggested that all organisms should first be divided into three large groups called domains. Archaea and Bacteria are two of these domains. The third domain is Eukarya
• Archae


  Organisms in this domain look similar to bacteria but are actually quite different as differences in their DNA and RNA sequences show. They were first found in extreme places such as hot springs and salt lakes.
• Bacteria


  contains true bacteria like E. coli and Staphylococcus.
• Eukarya


  includes a broad range of organisms including fungi, plants, animals and protists
• Selective Breeding


  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. for example:

  
  

  Animals that produce more meat or milk.

  Crops with disease resistance.

  Dogs with a good, gentle temperament-

  Plants that produce bigger fruit.

  
  

  This is the basic process involved in selective breeding:

  
  

  1) From your existing stock select the ones which have the characteristics you're after.

  
  

  2) Breed them with each other.

  
  

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

  
  

  4) Continue this process over several generations, and the desirable trait gets oventually, all the offspring will have the characteristic

  
  

  Selective breeding is nothing new people have been doing it for thousands of years. It's how we ended up with edible crops from wild plants and how we got domesticated animals like cows and dogs.

  
• Selective Breeding Advantages


  Selective breeding is important in agriculture. For example:

  
  

  Genetic variation means some cattle will have better characteristics for producing meat than others (e.g. a larger size). To Improve meat yields, a farmer could select cows and bulls with these characteristics and breed them together. After doing this, and selecting the best of the offspring for several generations, the farmer would get cows with a very high meat yield.

  
  

  It's also used in medical research. For example:

  
  

  In several studies investigating the reasons behind alcoholism, rats have been bred with either a strong preference for alcohol or a weak preference for alcohol. This has allowed researchers to compare the differences between the two different types of rats, including differences in their behaviour and in the way that their brains work
• Selective Breeding Disadvantages


  1) The main problem with selective breeding is that it reduces the gene pool the number of different alleles (forms of a gene) in a population. This is because the "best" animals or plants are always used for breeding and they are all closely related. This is known as inbreeding.

  
  

  2) Inbreeding can cause health problems because there's more chance of the organisms inheriting harmfu genetic defects when the gene pool is limited. Some dog breeds are susceptible to certain defects because of inbreeding, e.g. heart disease in boxer dogs. This leads to ethical considerations particularly if animals are deliberately bred to have negative characteristics for medical research.

  
  

  3) There can also be serious problems if a new disease appears. There's not much variation in the population, so there's less chance of resistance alleles being present. All the stock are closely related t each other, so if one is going to be killed by a new disease, the others are also likely to succumb
• Plant Tissue Culture


  1) Tissue culture involves growing cells on an artificial growth medium-

  
  

  2) Whole plants can be grown via fissue culture it's really easy and really useful too. Plants grown this way can be made very quickly, in very little space and can be grown all year.

  
  

  3) The plants produced via tissue culture are also clones genetically identical organisms. This means you can use fissue culture to create lines of clones all with the same beneficial features, e-g- pesticide resistance, fasty fruit, etc. Here's how it works

  
• Plant Tissue Culture Method

  1) First you choose the plant you want to clone based on its characteristics e.g. a beautiful flower, a good fruit crop.

  
  

  2) You remove several small pieces of tissue from the parent plant. You get the best results if you take tissue from fast-growing root or shoot tips.

  
  

  3) You grow the tissue in a growth medium containing nutrients and growth hormones. This is done under aseptic (sterile) 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.
• Animal Tissue Culture


  Animal tissue culture is often used in medical research because it means that you can carry out all kinds of experiments on tissues in isolation. E.g. you can investigate the effect of glucose on cells in the pancreas by growing pancreatic cells in culture. Whole animals aren't grown via tissue culture

  
  

  It means that 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.

  
• Animal Tissue Culture Method

  1) First, a sample of the tissue you want to study, e.g. tissue from the pancreas, is extracted from the animal.

  
  

  2) The cells in the 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 that 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.
• Genetic Engineering


  Genetic engineering Involves modifying an organism's genome (its DNA) to introduce desirable characteristics
• Genetic Engineering Process


  1) Restriction enzymes recognise specific sequencess of DNA and cut the DNA at these points the pieces of DNA are left with sticky ends where they have been cut.

  
  

  2) Ligase enzymes are used to join two pieces of DNA together at their sticky ends.

  
  

  3) Two different bits of DNA stuck together are known as recombinant DNA.

  
• Vectors to Instert DNA into Other Organisms

  A vector is something that's used to transfer DNA into a cell. There are two sorts

  
  

  plasmids and viruses:

  
  

  Plasmids are small, circular molecules of DNA that can be transferred between bacteria.

  
  

  Viruses insert DNA into the organisms they infect.

  
  

  Here's how genetic engineering works:

  
  

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

  
  

  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

  
• GE in Agriculture and Medicine

  ) For example, in agriculture, crops can be genetically modified to be resistant to herbicides (chemicals that kill plants). Making crops herbicide-resistant means farmers can spray their crops to kill weeds, without affecting the crop itself. This can also increase crop yield.

  
  

  2) In medicine, as well as genetically engineering bacteria to produce human insulin, researchers have managed to transfer human genes that produce useful proteins into sheep and cows. E.g. human antibodies used in therapy for illnesses like arthritis, some types of cancer and multiple sclerosis. These proteins can then be extracted from the animal, e.g. from their milk. Animals that have organs suitable for organ transplantation into humans might also be produced in the future.

  
  

  3) However, there are concerns about the genetic engineering of animals. It can be hard to predict what effect modifying its genome will have on the organism many genetically modified embryos don't survive and some genetically modified animals suffer from health problems later in life.

  
  

  4) There are also concerns about growing genetically modified crops. One is that transplanted genes may get out into the environment. E.g. a herbicide resistance gene may be picked up by weeds, creating a new 'superweed' variety. Another concern is that genetically modified crops could adversely affect food chains or even human health.
• GMO for insect resistance

  1) One reason why people might want to genetically engineer crops is to make them resistant to insect pests. This can improve crop yields and reduce the need for chemical pesticides.

  
  

  2) There's a bacterium called Bacillus thuringiensis (Bt) which produces a toxin (poison) that kills many of the insect larvae that are harmful to crops.

  
  

  3) The gene for the Bt toxin is inserted into crops, such as con and cotton, which then produce the toxin in their stems and leaves making them resistant to the insect pests.

  
  

  4) The toxin is specific to insect pests it's harmless to humans, animals and other insects. However, the long-term effects of exposure to Bt crops aren't yet known.

  
  

  5) The insects that feed on the crops are constantly exposed to the toxin, so there's s danger they'll develop resistance and no longer be killed by it. Farmers try to avoid this happening by using other insecticides foo.

  
• GMO for Food Insecurity

  1) The world's population is rising very quickly and it's not slowing down.

  
  

  2) This means that global food production must increase too so that we all have access to enough food that is safe for us to eat and has the right balance of nutrition- this is known as 'food security.

  
  

  3) GM crops can be used to help increase food productione.g. crops that are genetically engineered to be resistant to pests or to grow better in drought conditions can help to improve crop yields.

  
  

  4) Some crops can be engineered to combat certain deficiency diseases, e.g. Golden Rice has been genetically engineered to produce a chemical that's converted in the body to vitamin A.

  
  

  5) However, not everyone thinks this is a good idea:

  
  

  1) Many people argue that people go hungry because they can't afford to buy food, not because there isn't any food about. So they argue that you need to tackle poverty first.

  
  

  2) There are fears that countries may become dependent on companies who sell GM seeds.

  
  

  3) Sometimes poor soil is the main reason why crops fail, and even GM crops won't survive.
• Other Methods to Increase Food Production

  1) Using GMOs is a relatively new way of improving crop yields and it might not always be helpful.

  
  

  2) For example, if soils are poor, applying fertilisers is likely to be the best way to increase yields. Fertilisers contain minerals that are essential for plant growth, e.g. nitrates and phosphates. They replace the nutrients that have been lost from the soils to previous crops. However, excess fertilisers can cause problems in rivers and lakes through the process of eutrophication

  
  

  3) Pests can also be controlled without the use of GM crops or chemical pesticides. Biological control methods use other organisms (including predators and parasites) to reduce pest numbers. For example, cane toads were introduced into Australia to eat beetles that were damaging crops.

  
  

  4) Biological control can have longer-lasting effects than chemical pesticides and be less harmful to wildlife, but introducing new organisms can cause problems, e.g. cane foads are now a pest themselves in Australia because they poison the native species that eat them.