5.4: Evolution Evolution is the cumulative change in the heritable characteristics of a population. SPECIES AND POPULATIONS EVOLVE INDIVIDUALS DO NOT EVOLVE 5.4.2: Fossil record A fossil is any physical evidence about a dead organism. Some fossils are only fragments of bone, teeth or shells. Amber fossils sometimes contain intact bodies of insects and small amphibians. Rock fossils show complete details of external structures. 5.4.2: Homologous structures Structures derived from the same body part of a common ancestor are called homologous structures. One example of a homologous structure is the pentadactyl limb, which is an appendage comprised of five bones. 5.4.2: Selective breeding Selective breeding is the process used by breeders to develop a plant or animal over time with desired characteristics. 5.4.3: Overpopulation STATE: Populations tend to produce more offspring than the environment can support 5.4.4: Struggle for survival Populations tend to produce more offspring than the environment can support; and this over-production of offspring results in a struggle for survival. The ‘fittest’ individuals are those with the best genes; in other words, those with the most favorable heritable variations. The ‘fittest’ individuals are the most likely to survive long enough to reproduce and pass on their genes; and the ‘weakest’ individuals are more likely to die young and not pass on their genes. N09/4/BIOLO/SP2/ENG/TZ0/XXExplain how sexual reproduction can lead to variation in a species.  allows characteristics from both parents to appear in offspring; crossing over (during prophase 1) changes chromosome composition; produces gametes which are all different; random chance of which sperm fertilizes ovum; greater variation (resulting from sexual reproduction) favours survival of species through natural selection; [3 max] Accept independent assortment during meiosis from AHL. M08/4/BIOLO/SP2/ENG/TZ1/XX+ (b) Outline how sexual reproduction can give rise to genetic variation in a population. meiosis; crossing over; independent assortment; sexual reproduction/fertilization/recombination; mutations; environmental; [2 max] 5.4.5: Variation within a species STATE: Members of a species show variation 5.4.5: Sexual reproduction Variation exists between members of one species, which means that some individuals are better suited for survival than others. The sources of variation are: 1) mutation, which creates new alleles in the first place; 2) meiosis, which enables each parent to produce millions of different gametes (each with a unique combination of chromosomes); and 3) sexual reproduction, fertilisation and mate selection Individuals that are better suited to changes in the environment survive and pass on their genes for surviving 5.4.7: Natural Selection Deduction 1: Populations produce more offspring than the environment can support. Deduction 2: The over-production of offspring results in a struggle for survival and nature selects the ‘fittest’ individuals. Deduction 3: The ‘fittest’ individuals survive long enough to reproduce and pass on their genes; the ‘weakest’ individuals die young and fail to pass on their genes. Thus natural selection leads to the increased reproduction of individuals with favorable heritable variations. Charles Darwin Alfred Wallace 5.4.8: Evolution in Response to Environmental Change Name of population: The tuberculosis bacterium Characteristic under evolution: Resistance to the antibiotic Rifampicin Environmental change: Exposure to an inadequate dose (or inadequate duration) of the antibiotic Response 1: When patients receive an inadequate dose (or inadequate duration) of the antibiotic then some of the bacterial population may survive. Each bacterium that is killed by the antibiotic has a particular allele that codes for the particular protein that the antibiotic targets. And conversely, each bacterium that survives the antibiotic must be lacking the particular allele that codes for the particular protein that the antibiotic targets. Response 2: When a surviving bacterium divides it passes on its antibioticresistant allele to its two daughter cells. Having inherited the antibiotic-resistant allele, the two offspring survive, reproduce and increase the antibiotic-resistance gene in the population. After several generations the population can become resistant to the antibiotic. Natural Selection DDT Resistance in Anopheline Mosquitoes The malarial parasite is spread by anopheline mosquitoes The spread of malaria can be controlled by controlling mosquito numbers DDT One way of controlling mosquito numbers is to use an insecticide like DDT Not every mosquito will be killed each time we spray Some will survive to repopulate the area, so… …we must spray frequently. Random mutation may produce mosquitoes which are resistant to the effects of DDT… …these are more likely to survive and pass on their genes to the next generation NOTE A resistant mosquito does not need to be totally immune to the effects of DDT… … it may just be able to survive higher does of DDT than ‘normal’ mosquitoes. The next generation contains more resistant mosquitoes Again, they are more likely to survive to reproduce, so… …the proportion of the population which is resistant to DDT increases With each successive generation… …the proportion of the mosquito population which is resistant to DDT increases. Eventually,… …the whole population may consist of resistant mosquitoes Spraying with DDT produces the selective pressure which favours the resistant mosquitoes. Because they can resist the effects of DDT, the resistant mosquitoes are said to have a selective advantage It may not be able to increase the dose of DDT used: - higher doses may be dangerous to humans - higher doses may be too damaging to other wildlife Using higher doses of DDT will also produce the selective pressure which will favour mosquitoes with even higher levels of resistance Explain how natural selection can lead to evolution using antibiotic resistance in bacteria as an example.  M11/4/BIOLO/SP2/ENG/TZ2/XX members of a population of the same species show variation; some organisms are more likely to survive due to selective advantage / survival of the fittest; some organisms have a reproductive advantage; these variations may be genetically controlled/heritable; these genes are most likely to be passed on to offspring; this can change the characteristic of the population; bacteria can normally be killed with antibiotics; antibiotics impose a selection pressure; if a few bacteria have natural resistance to the antibiotic they will survive; if the resistance is heritable they will pass it on to their offspring; they will reproduce/evolve to form bacterial colonies resistant to the antibiotic; example of organism selected by use of antibiotic; (e.g. MRSA bacteria / resistant TB bacteria) [9 max] M08/4/BIOLO/SP2/ENG/TZ1/XX+ (c) Explain two examples of the evolution of specific populations of organisms in response to environmental change.    Two examples required. Award [4 max] for each example. Example 1 name of population and characteristic: e.g. antibiotic resistance in bacteria (for example Gonorrhea); environmental change: exposure to the antibiotic; response 1: antibiotic-sensitive bacteria die / antibiotic-resistant ones survive; response 2: pass on antibiotic-resistance gene/inherited trait; drug-resistance gene transferred to other bacteria (by plasmids); over time resistance in the population is increased; Example 2 name of population and characteristics: Galapagos finches, some with strong/big beaks and some with small beaks; environmental change: wet years with abundant small seed change to drought years with only large seeds (as a prevalent food source); response 1: small beaked finches die leaving primarily finches with strong/large beaks / vice versa; response 2: finches with large beaks survive to pass gene/inherited trait to offspring; over time large beaks predominate; [8 max] M06/4/BIOLO/SP2/ENG/TZ1/XX Explain briefly how natural selection could lead to evolution.  species produce more offspring that can survive; populations will show variation; individuals with favourable traits will survive; some variations are inherited; favourable (inherited) variations will increase in numbers; accept converse answer environmental changes will provide further selection; sustained selection of favourable traits will result in evolution / results in speciation; [3 max] Evolution or speciation must be addressed in order to receive full marks. N.B. Examples are acceptable only if they support marking points given above. M05/4/BIOLO/SP2/ENG/TZ2/XX Discuss the theory of evolution by natural selection. species produce more offspring that can survive; populations will show variation; individuals with favourable traits will survive; some variations are inherited; favourable (inherited) variations will increase in numbers; accept converse answer environmental changes will provide further selection; sustained selection of favourable traits will result in evolution / results in speciation; Evolution or speciation must be addressed in order to receive full marks. N.B. Examples are acceptable only if they support marking points given above.