Chapter 10


Classification systems

Classification is the name given to the process by which living organisms are sorted into groups where they share similar features The most common classification is the taxanomic groups, kingdom, phyla, class, order, genus, species. Kindgdoms being the broadest taxanomic group and species being the smallest and most specfic classification. Based on further stidies of genetic material, a further level of classification is the three domain systems, which is placed o the top of the hierachy. Scientists classify organisms in order to:

  • Identifying species - by using a clearly defined system of classification, the species an organism belongs to can be easily identified.
  • Predicting characteristics - if several members in a group have a specific characteristic, it is likely another species in the group will have the same characteristic.
  • Finding evolutionary links - species in the same griup probably share characteristics because they have evolved from a common ancestor.

By using a single classification system, scientists worldwide can share their research and links can be seen between organisms even if they are on different continents, and it means that common names do not become a hindering factor.

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How organisms are classified

The classification begins by seperating the organism into 3 domains, Archae, Bacteria, and Eukarya which are the broadest groups. As you go down the groups the organisms in them become more similar and share more characteristics. The system ends with an organism being classified as an induvidual species, where each group only contains one type of organism. A species is defined as a group pf organisms that can reproduce to produce fertile offspring. For example donkeys can reproduce to form fertile offspring, but cannot breed with a horse to produce fertile offspring as mules contain an odd number of chromosomes and so meiosis and gamete production cannot occur normally as all the chromosomes cannot pair up. Humans belong in the species Homo sapiens.

Before classification systems were widely used, organisms were given names according to their physical characteristics, which is not useful for scientists working internationally as many organisms have more than one common name, and that they do not provide any information about the relationships between organisms, so to ensure scientists all over the world are discussing the same organism, a system was developed called binomial nomenclature.

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Binomial nomenclature

All species are given a scientific name consisting of two parts:

  • The first word indicates the organism's genus, and is called the generic name, and is equivalent to a family name shared by close relatives.
  • The second word indicates the organism's species, the specific name.
  • No two species have the same generic and specific name, two species could have the same specific or generic name, but never both combined.

When naming an organism using its scientific name the word should be presented in italics, or underlined in handwriting. The name should be written in lowercase, with the exception of the first letter of the genus name which should be uppercase.

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The five kingdoms

The five kingdoms are:

  • Prokaryotae (bacteria) [prokaryote]: Unicellular, no nucleus or other membrane bound organelles, a ring of naked DNA, small ribosomes, no visible feeding mechanism - nutrients are absorbed through the cell wall or interally by photosynthesis.
  • Protoctista (the unicellular eukaryotes) [eukaryote]: Mainly unicellular, a nucleus and other membrane bound organelles, some have chlorplasts, some are sessile but others move by cilia, flagella or amoeboid mechanisms, nutrients are aquired by photosynthesis (autotrophic), ingestion of other organisms (heterotrophic) or both (parasitic).
  • Fungi (yeasts, moulds, mushrooms) [eukaryote]: unicellular or multicellularm a nuclues and other membrane bound organelles, a cell wal composed of chitin, no chloroplasts or chlorophyll, no mechanisms for locomotion, most have a body of mycelium made of hyphae threads, nutrients are aquired by absorption - mainly from decaying matter (saprophytic), store food as glycogen.
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The five kingdoms II

  • Plantae (plants) [eukaryote]: second largest with 250,000 species, multicellular, a nucleus and other membrane bound organelles including chloroplasts, all contain chlorophyll, a cell wall made of cellulose, sessile apart from some gametes that move using flagella or cilia, nutrients aquired by photosynthesis (autotrophic feeders) - organisms that make their own food, store food as starch
  • Animalia (animals) [eukaryote]: largest kingdom with over 1 million species, multicellular, a nucleus and other membrane bound organelles, no cell walls, no chloroplasts or chlorphyll, move with the aid of cilia, flagella or contractile proteins, sometimes in the form of muscular organs.

When an organism evolves, as does thier DNA, as it is the DNA that determines the proteins that are made which determine the organism's characterstics, by comparing similarites in DNA scientists can can discover new evolutionary links between them and can be used to impove the classification system.

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The three domains system

Domains are a further level of hierachy recently introduced as a result of the study of DNA. This system groups organisms using differences in the sequences of nucleotides in the cells rRNA, as well as their membranes' lipid structure and sensitivity to antibiotics. Observation of these differences was made possible through advances in scientific techniques. Under the Three Domains System, organisms are classified into 3 domains and 6 kingdoms. The three domains are Archae, Bacteria and Eukarya, each of which contai a unique form of rRNA and different ribosomes. Eukarya - 80s ribosomes, RNA polymerase contains 12 proteins. Archae - 70s riboaomes, RNA polymerase has between 8-10 proteins, very similar to eukaryotic ribosomes. Bactera - have 70s ribosomes. RNA polymerase contains 5 proteins. In this system the Prokaryotae kingdom gets divided into 2 kingdoms, Archaebacteria and Eubacteria, so there are 6 kingdoms: Archaebacteria, Eubacteria, Protoctista, Fungi, Plantae and Animalia. Although  Archaebacteria and Eubacteria are single celled prokaryotes, Eubacteria are classified on ther own because their chemical makeup differs, for example they contain peptidoglycan in their polymers which  Archaebacteria do not.

Archaebacteria are known as ancient bacteria because they are extremophiles, and can live in harsh conditions like hydrothermla vents and acidic environments. Eubacteria are called true bacteria, are found in all environments and are the most common.

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Phylogen is the name given to the evolutionary relationships between organisms. The study of evolutionary history of groups of organisms is known as phylogenetics, and reveals which group a particular organism is related to, and how closely related these organisms are. Classification can occur without any knowledge of phylogeny, but scienstists aim for it to take this into account. A phylogenetic tree is a diagram used to represent the evolutionary relationships between organisms, and are branched diagrams showing how different species have evolved from a common ancestor. The earliest species is found at the base of the tree, and the most recent species at the tips of the branches, these trees are produced by looking at similarities and differences in species' physical and genetic characteristics, mainly gained through fossils. Phylogeny can be done without reference to classification, and classification uses knowledge of phylogeny to confirm whether classification groups are correct or need to be changed. Other advantages include:

  • Phylogeny produces a continuous tree whereas classification requires discrete taxanomical groups, scientists are not forced to put an organism into a specific group they do not quite fit.
  • The hierchial nature of Linnaean classification can be misleading as it implies different groups within the same rank are equivalent, for example different groups cannot be comparable.
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Evolution is a theory which describes the way in which organisms evolve, or change, over many many years as a result of natural selection. Darwin realised that organisms best suited for their environmnent are more likely to survive and reproduce, passing their characteristics on to their offspring. Gradually a species changes over time to have a more advantageous phenotype for the environment that which it lives, we now know that the advantageous characteristics are passed from one generation to the next by genes in a DNA molecule. Key points:

  • 1831 - Darwin reads 'Principles of Geology' by Lyell, who suggests fossils are evidence of animals that lived millions of years ago and the principle of uniformitarianism - the idea that in the past the earth was shaped by forces we can still see today in natural processess. This promoted Darwin to think of evolution as a slow process, one in which small changes gradually accumulate over a very long period of time.
  • Darwin carried out some of his most famous observations in on finches in the Galapagos Islands, where ne noticed that different finches have different beak and claw shapes which was linked to the food source on each of the Islands, and concluded that a bird born with a more suited beak woul survive longer and have more offspring, and over time this characterstic would be shared by the whole finch population.
  • Darwin published 'On the origin of Species' in 1859 after presenting them in 1858.
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Fossils are formed when animal and plant remains are preserved in rocks, over long periods of time, sediment is deposited on the earth to from strata of rock. Different layers correspond to different geological areas, the most recent layer being found on the top. Within the different straya the fossils found are quite different, forming a sequence from oldest to longest, which shows how the organisms have gradually changed over time. This is known as the fossil record:

  • Fossils of the simplest organisms such as bacteria and simple algae are found in the oldest rocks, whilst fossils of more complex organisms such as veterbrates are found in the more recent rocls, supporting the evolutionary theory that simple life forms gradually evolved over an extremely long time period into more complex ones.
  • The sequence in which organisms are found matches their ecological links to each other, for example plant fossils appear before animal fossils, as animals need plants to survive
  • By studying similarities in the anatomy of fossil organisms, scientists can show how closely related organisms have evolved from the same ancestor.
  • Fossils allow relationships between extinct and living organisms to be investigated.
  • However the fossil record in not complete as many organisms are soft bodied and decompose quickly before they have a chance to fossilise, and the conditions needed for fossils to form are not often present, others destroyed by Earth's movements.
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Comparative anatomy

Comparative anatomy is the study of similarities and differences in the anatomy of living structures. 

homologous structure is a structure that appears to be different and may perform different functions in different organisms, but has the same underlying structure, such as the pentadactyl limb of veterbrates. These limbs are used for a a wide variety of functions such as running, jumping, and flying. You would expect the bone structure of these limbs to be very different, however the bsic structure of all veterbrate limbs are actually very similar - the same bones are adapted to carry out a whole range of different functions, an explanation is that all veterbrates have evolved from a common ancestor, therefore they limbs have all evolved from the same structure. The presence of homologous structures provides evidence for divergent evolution, which describes how, from a common ancestor different species have evolved each with a different set of adaptive features, which occurs when a closely related species diversify to adapt to new habitats as a result of migration or a loss of habitat. 

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Evolutionary embryology

Embryology is the study of embryos. It is another source of evidence to show evolutionary relationships, an embryo is an unborn animal in its earliest phases of development. Embryos of many different animals look very similar and it is often difficult to tell them apart, showing that the animals develop in a similar way, implying the processes of embryonic development have a common origin and the animals share a common ancestry but have gradually evolved different traits. Many traits of one type of animal apper in the embryo of another, for example both fish and human embryos have gill slits, which disappear in humans before birth, so evolutionary history can be traced in the developemt of its embryos, as new organs or structures evolved with develop at the end of an organism's embyonic development.

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Comparative biochemistry

Comparative biochemistry is the study of similarites and differences in the proteins and in the other molecules that control life processes. Although these molecules can change over time, some important molecules are highly conserved (remain almost unchanged) among species. Slight changes in these molecules can help identify evolutionary links, two of the most common studied are rRNA and cytochrome c ( a protein involved in respiration). The hypothesis of neutral evolution is that msot of the variability in the structure of a molecule does not affect its function, as most of the variability occurs outside the molecule's functional regions. Changes that don't affect a molecule's function are called neutral, and these neutral substitutions occur at a fairly regular rate. 

To discover how closely two species are related, the molecular sequence of a particular molecule is compared, which is done by looking at the order of the DNA bases or the order of amino acids in the protein. The number of differences is plotted against the rate the molecule undergoes neurtral base pair substitutions. From this information scienstists can estimate the point at which the 2 species last shared a common ancestor. Species that closely related have more similar DNA and proteins, whereas the distantly related have far fewers similarities. rRNA has a very slow rate of neutral substitution, so it is commonly used with together with fossil information to determine the relationship between ancient species. 

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Types of variation

The difference in characteristics between organisms are called variations. The widest type of variation is between members of different species, these differences are known as interspecific variation. Differences between organisms within a species as called intraspecific variation. Variation arises due to an organism's genetic material-differences in the genetic material it inherits from its parents leads to genetic variation, and also due to the environment in which the organism lives - this causes environmental variation.

Many studies have been carried out on indentical twins, which are produced when an egg splits after fertilisation and contain the same genetic material, to determine how much of certain characteristics are a result of genetic variation, and how much is due to the environment that which a person lives. If the twins are brought up in different environments, the characteristics they show the most variation in will be influenced more greatly by the environment than by genes, and the same vice versa.

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Genetic causes of variation

Genetic variation is due to the genes and alleles an individual posses and is caused by:

  • Alleles (variants) - genes have particular alleles (alternative forms). With a gene for a particular characteristic, different alleles produce different effects. For example the gene for human blood groups has 3 different alleles and depending on the combination of these inherited from parents determines an individual's blood type.
  • Mutations - changes in the DNA sequence and therefore to genes can lead to changes in the proteins that are coded for, and these protein changes can affect physical and metabolic characteristics. If a mutation occurs in somatic cells, just the individual is affected, however if a mutation occurs in the gametes, it may be passed on to the organism's offspring.
  • Meosis - gametes are produced in the process of meiosis in organisms that produce sexually. Each gamete recieves half the genetic content of a parent cell. Before the nucleus divides and the chromatids of a chromosome seperate, the genetic material is mixed up as a result of independant assortment and crossing over, leading to the gametes of an individual showing variation.
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Genetic causes of variation II

  • Sexual reproduction - the offspring produced from two individuals inherits genes (alleles) from each parent, so each individual produced therefore differs from the parents.
  • Chance - many different gametes are produced from the parental genome, during sexual reproduction it is a result of chance as to which two combine (often referred to as random fertilisation). The individuals produced therefore also differ from their siblings as each contains a unique combination of genetic material.

Many of these are all aspects of sexual reproduction. As a result their is much greater variation in organisms that produce sexually rather than asexually. Asexual reproductin results in the production of clones, and genetic variation can only be increased in these organisms as a result of mutation. An example of a characteristic that is determined purely by genetic variation is your blood group, as the genes passed on to you from your parents will determine this.

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Environmental causes of variation

All organisms are affected by the environment in which they live, although plants will be affected to a greater degree due to their lack of mobility, as plants in sunlight for example will grow larger than those not in sunlight. An example of a characteristic that is determined pureply by environmental variation is the prescence or absence of any scars and have no genetic origin.

In mst cases variation is caused by a combination of both environmental and genetic factors, for example if you have tall parents you are likely to inherit the genes to also grwo tall, but if you have a poor diet or suffer from disease you may noy. Another example is skin colour, as this is determined by how much melanin you have in your skin, at birth this is controlled purely by genetics, but depedning on how much you expose ypur skin to sunlight the more melanin you produce to protect your skin from UV rays, resulting in the skin becoming darker. Ad many characteristics are caused by a combination of both factors, it can be very difficult to draw conclusions about the causes of variation in any particular case, and this is often referred to as the 'nature versus nurture' argument. 

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Continuous and discontinuous variation

When studying variation, scientists need to take measurements of different characteristics within a species, from large numbers of a population and then represented graphically so the data can be analysed and interpreted. Characteristics can be sorted into those that show discontinuous variation and continuous variation. 

Discontinuous variation are characteristics that can only result in certain values - they are discrete. Variation determined purely by genetic factors falls into this catergory, for example an animal's sex or one of the shapes bacteria can take. Discontinuius variation is usually represented using a bar or pie chart, to show the discrete values, such as blood type, which is controlled by a single gene.

Continuous variation is shown when a characteristic can take any value within a range - known as a continuum as there is a graduation in values from one extreme to the other of a characteristic. Characteristics that show continuous variation are not controlled by a single gene but a number of genes (polygenes) and are also often influenced by environment. Data on characteristics that show continuous variation are collected in a frequency table and the data is then poltted on a histogram, and a curve is usually drawn to show the trend.

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Standard Deviation

When continuous variation data are plotted on to a graph, they usually result in the production of a bell shaped curve known as a normal distribution curve, where the mean, mode, and median are the same, their is a characteristic bell shape which is symmetric about the mean, 50% of the values are less than the mean and 50% aare greater, so most values lie close to the mean and the number of individuals at the extremes of the range are low.

Standard deviation is a measure of how spread the data is. The greater the standard deviation, the greater the spread of the data, in terms of variation, a characteristic which has a high standard deviation has a large amount of variation. When you calculate the standard deviation of data that displays normal distribution you will find that 68% are within 1 standard deviation of the mean, 95% of values are within 2 standard deviations of the mean, and that 99.7% of values are within 3 standard deviations of the mean. x = the value measured and -x = mean, n = total number of values in the sample, have to calculate the sum of each measured value minus the mean, square each of these values, divide by sample size - 1, and then sqaure root.

{\displaystyle s={\sqrt {\frac {\sum <em>{i=1}^{N}(x</em>{i}-{\overline {x}})^{2}}{N-1}}}.}

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Student's t test

This test is used to compare the means of data values of two populations by using their standard deviations. Before calculating this you must produce a null hypothesis, which is a prediction that there will be no significant difference between the 2 specified populations, and at the end this can be rejected or accepted depending on what the df value says the percentage probability will be from looking at the data table. If the p value is under 0.5, it is nor significant and the null hypothesis will be accepted.  S1 and S2 are the standard deviations of populations 1 and 2, and -x1 and -x2 are the mean populationsm n1 and n2 are the total number of the samples in each population.

Related image

Once t has been calculates you calculate degrees of freedom through df = (n1+n2) - 2, and then look at corresponding p value on table given, to see if the null hypothesis should be accpeted or rejected.

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Spearman's rank

Spearman's rank correlation coefficient is used to consider the relationship between two sets of data, and whether they show no correlation - no relationship between the data, positive correlation - as one set of data increases in value, so does the other, and negative correlation - as one set of data increases in value, the other decreases in value. Rs is the correlation coefficient, d = difference in ranks, n = number of pairs of data. The data given in two tables needs to be rank ordered, from lowest to highest, where if two things have the same value the rank will be +0.5 as an average. Rank both sets of data measurements, then work out the difference between the two ranks in the same column and data pair, then square this, then add all of them to get the sum of d squared.

Spearman's Rank Correlation Coefficient Formula

An Rs value of +1 shows a perfect positive correlation, an RS value of -1 shows a perfect negative correlation, and an Rs of 0 shows no correlation.

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Anatomical adaptations

Adaptations are characteristics that increase an orgnanisms chances of survival and reproduction in its environment, it is divided into anatomical - physica features (internal and external), behavioural adaptations - the way an organism acts as a result of inheritance or learning, and physiological adaptations - proceses that take place inside an organism. Many adaptations fall into more than one category. Some examples of anatomical adaptations:

  • Body covering - animals have a number of different body coverings such as hair, scales, spines and feathers, which can help the organism to fly, stay warm or provide protection. The thick waxy layers on plants prevent water loss and spikes deter herbivores and protect tissues from sun damage.
  • Camoflage - the outer colour of an animal allows it to blend into its environment, making it harder for predators to spot it, for example the snowshoe hair is white in the winter to match the snow and turns brown in the summer to blend with the soil.
  • Teeth - the shape and type of teeth presnt in an animal's jaw are related to its diet, herbivores like sheep have continuosly growing molars for chewing tough grass and plants, carnivores such as tigers have sharp large canines to kill prey and tear meat.
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Anatomical adaptations II

  • Mimicry - copying another animal's appearance or sound allows a harmless organism to fool predators into thinking that is is poisonous or dangerous, for example the harmless hoverfly mimics the markings of a wasp to deter predators.

Marram grass - this plant is commonly found in sand dunes and is a xerophyte, its adaptations to reduce transpiration rate include:

  • Curled leaves to minimise the surface area of moist tissue exposed to the air, and protect leaves from the wind.
  • Hairs on the inside surface of the leaves to trap moist air close to the leaf, reducing the diffusion gradient of water vapour.
  • Stomata sunk into pits, which make them less likely to open and lose water, and be affected by winds or air  climate.
  • A thick waxy cuticle on the leaves and stems, reducing water loss through evapouration.
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Behavioural adaptations

  • Survival behaviours - for example a rabit freezes when they think they have been seen.
  • Courtship - many animals exhibit elaborate courtship behaviours to attract a mate, for example scorpions perform a dance to attract a mate, increasing an organism's chance of reproducing.
  • Seasonal behaviours - these adaptations enable organisms to cope with changes in their environment, they include migration, where animals move from one region to another and then back again when conditions are more favourable, this may be for a better climate or better source of food, and hibernation, which is a period of inactivity in which an animal's body temperature, heart, and breathing rate slow down to conserve energy, reducingthe animal's requirement for food, eg brown bare hibernate during the winter.

Generally, behavioural adaptations fall into two main catergories:

  • Innate (instinctive) behaviours - the ability to do this is inherited through genes, such as the behaviour of spiders to build webs or for woodlice to avoid light. This allows the organism to survive in the habitat in which it lives.
  • Learned behaviour - these adaptations are learnt from experience or from observing other animals, one example is the use of tools to break a shell or nut for food.
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Physiological adaptations

Some examples of physiological adaptations include:

  • Poison production - many reptiles produce venom to kill their prey and many plants produce  poisons in their leaves to protect themselves from being eaten.
  • Antiobiotic production - some bacteria produce bacteria to kill other species of bactria in the surrounding area.
  • Water holding - the water holding frog can store water in its body, allowing it to survive in the desert for more than a year without access to water, many cacti and xerophytes can hold large amounts of water in their tissues.
  • Many other examples are less unusal such as reflexes, blinking and temperature regulation.
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Convergent evolution

Analogous structures are anatomical adaptations that have a different genetic origin but have adapted to perform the same role, such as the tail fins of a whale and a fish. This is an example of convergent evolution as it demonstrates how unrelated species begin to share similar traits as a result of evolving in a similar environment or adapting to similar selection pressures as the organisms live in a similar way to each other. Examples include:

  • Marsupial and placental mice - these species resemble each other despite a larger temporal and geographical seperation between Australia and America because they have adapted to fill similar niches. These two subclasses of mammal (marsupial that develop mainly in the pouch by suckling milk and placental mammals that are connected to their mother's circulatory system in the uterus through a placenta, so reach a high level of maturity before birth) seperated from a common ancesteor millions of years ago, but have a stron resemblance in overall shape, locomotion and feeding techniques. This is because they have adapted to simialr climates and food supplies, as both are small agile and forage at night in dense ground cover, but have very different methods of reproduction, reflecting their distinct evolutionary relationships.
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Convergent evolution II

  • Marsupial and placental moles both burrow through soft soil and have a streamlined shape and modified forelimbs for digging and have smooth fur to allow movement through soil, but do differ in fur colour.
  • Flying phalangers and flying squirrels - both are gliders that eat insecrs and plants, their skin is stretched between their forelimbs and hind limbs to provide a large surface area for gliding from one tree to the next, but both are different species.
  • Convergent evolution can also be seen in some plant species, for example aloe and agave appear very similar as both have adapted to survive in the desert, However both species developed entirely seperately from each other as Aloe evolved in sub-Sahara Africa whereas Agave evolved in Mexico and southern U.S.A.

Classification of giant pandas -  in what family this species belong has been discussed for many years due to its similarities with the red panda (eats bamboo in same manner and have similar snoouts/paws) and the bear (similar shape and size, walk and climb in same manner), as giant and red pandas may have developed similar characteristics as a resul of convergent evolution, but the same could apply to their resemblacne to bears. Now due to molecular level analysis we can see that the giant panda has greater serological affinities with the bear than the racoon, and so is a true bare that must have differentiated early in history from other bears.

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Natural selection

All organisms are expose to selection pressures, which are factors that affect the organisms chances of survival or reproductive success, as organisms best adapted to their environment are more likely to survive and reproduce, these adaptations will become more commo in the population, organisms that are poorly adapted are less likely to survive and so their characterstics are not passed on to the next generation, Naturals selection occurs in a number of steps:

  • Organisms within a species show variation in their characteristics that are caused by genetic variation, varying alleles or new alleles arising by mutation.
  • Organisms whose characteristics are best adapted to a selection pressyre suchas predation, competition or disease have an increased chance of survival and reproduction, and less well-adapted organisms die or fail to reproduce, this is known as survival of the fittest.
  • Succesful organisms pass the allele encoding the advantageous characteristic onto their offspring. Conversely organisms that have the non-advantageous allele are less likely to.
  • This proces is repeated over every generation and over time the proportion of individuals with the advantageous allele increases and so the frequency of the allele increases in the gene pool. Over long periods of time, multiple generations and multiple genes, this process can lead to the evolution of a new species.
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Modern examples of evolution

Antibiotic resistant bacteria - MRSA has developed resistance to many antibiotics as bacteria reproduce very rapidly so can evolve quickly, as when bacteriar replicate their DNA can be altered, which usually results in the bacteria dying, but in this case the mutation caused a resistance to methicillin, as when the bacteria were exposed to thhis antiobiotic, resistant individuals survived and reproduced, passing on the allele for resistance on to their offspring whilst whilst the non resistant indidviduals died so over time the amount of resistance in the population increased.

Peppered moths: Dramatic chages in the moth's environment due to the industrial revolution caused darker colour moths to become more present in the population as a result of better adaptation to the darker environment, this was as a result of pollution and loss of lichen causing the trees and environment to become darker, and the paler ones adapted to tree bark were no longer adapted to the environment. This resulted in a higher frequency of the dark allele in the moth gene pool and the number of dark peppered moths became much higher than pale ones close to industrial towns. Since air quality has improved in towns and cities since then the bark on trees is a again a lighter colpur so the frequency of the pale allele in the moth gene poll has now increased.

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Modern examples of evolution II

Sheep blowflies: Thess insetcs lay their eggs in the faecal matter arounf the sheeps tail and the larvae then hatch to cause sores, which can be fatal. In the 1950s the pesticide diazinon was used to kill the blowflies but within 6 years the flies had developed a high level of resistance to diazinon and individual insects with resistance survived expose and passsed on their characteristic through their alleles, allowing a resistant population to evolve. After researching this rapid developing resistance scientists found that there was a pre existing chemical to this chemical, and concluded that this pre-adaptation contributed to the development of diazinon resistance. Pre-adaptatin is when an organism's existing trait is advantageous for a new situation, and alteration in the DNA that caused the pre existing resistance to organophosphate chemicals, and ultimately a specific diazinon resistance allele. The existence of pre-adaptation in an organism may help researchers predict potential insecticide resistance in the future.

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Modern examples of evolution III

Flavobacterium: Most evolution occurs as a negative result of selection pressures. However some organisms have evolved due to oppertunities that have arisen in their environment. For example scientists have found a new strain of flavobacterium living in waste water that has evolved to digest the nylon desposited from factories into the water and so is benefical to humans as it can clear factory waste. These bacteria use enzymes to digest bylon known as nylonases, which are unlike enzymes found in other strains of this bacteria and do not help the bacteria digest any other known material, it is beneficial to the bacteria as it provides them with another source of nutrients. Most scientists believe that the gene mutation that occured to produce these enzymes was a result of gene duplication combined with the insertion or deletion of DNA bases that caused the genetic code to be read incorrectly, and result in the synthesis of a new enzyme.

When a few individuals of a species colonise a new area, their offpsring initially experience a loss in genetic variation, often resulting in individuals that are physically and genetically different to thier source population, this is known as the founder effect, and after this period the species then begin to show similar traits as natual selection occurs gradually.

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