1. Evidence of evolution that the mechanisms of inheritance, accompanied by selection, allow change over many generations
x Outline the impact on the evolution of plants and animals of: - Evolution refers to the biological changes from simple to more complex organisms - In a stable environment the characteristics present in a population as a whole do not
change a great deal (e.g. crocodiles) - If an environment suddenly changes, animals that have adapted to the stable
environment would no longer be best suited (becoming extinct), whereas those with characteristics better suited would survive and reproduce, possibly causing a change in appearance
- Changes in physical conditions in the environment � Physical conditions include; rainfall, temperature, rock type, wind � Example - Snow gums (found in high altitude areas of NSW): as the altitude
increases, the height and leaf length decrease, bark is thinner, fruit is larger (more resistant to frost)
� Example - Tasmanian wombats, wallabies and possums: all larger than those on the mainland = they have a smaller surface area to volume ratio (don’t lose as much body heat)
� An experiment carried out to show this; place seeds of different species from different areas under the same controlled conditions e.g. temperature, soil. Variations from natural habitat should be maintained if of different genetic variations
- Changes in chemical conditions in the environment � Chemical variations are largely the result of industrial contamination and the use
of pesticides � Example - Super rats: cannot be killed by traditional rat poisons (resistant)
- Competition for resources � Features that enable an individual to be able to obtain nutrients or produce and
care for their young effectively will dominate and survive through natural selection
� Example - Marsupial populations in Australia: rapid expansion after separation from Gondwana
x Describe, using specific examples, how the theory of evolution is supported by the following areas of study:
- Palaeontology, including fossils that have been considered as transitional forms � Fossils provide the most direct evidence that organisms have evolved over time � Darwin: the fossil record should yield intermediate forms (organisms that show
development from one group to another)
Archaeopteryx’s features shared with: Reptile Bird - Teeth - Feathers - Solid bones - Wish bone - Long tail - Wings
- Claws - No breast bone Crossopterygian’s features shared with: Fish Amphibians - Gills - Lobe fins (useful on land, could walk) - Fins - Lungs - Scales
- Biogeography � Biogeography is the study of the geographical distribution of both living and
extinct organisms � A species is a group of living organisms of similar individuals capable of
exchanging genes or interbreeding, producing fertile offspring under natural conditions
� The Darwin-Wallace theory of evolution proposes that, for new species to arise, a group of individuals must become isolated or geographically separated from the rest of the population
� Example - Finches on the Galapagos Islands: Darwin discovered the different types of finches (differentiated by their beaks which were suited to the food on that particular island) on the different islands of the Galapagos
� Example - Emu (Australia), Ostrich (South Africa), Kiwi (New Zealand), Rhea (South America): the present-day distribution of these flightless birds suggests they originated from a common ancestor on Gondwana and evolved on the isolated southern continents as they drifted apart
� However, the theory of biogeography relies on another theory, continental drift - Comparative embryology � Comparative embryology is the comparison of the developmental stages of
different species � Similarities may be used to infer relationships between organisms � Example - Fish, amphibians, reptiles, birds, mammals: show the presence of gill
slits and pouches with distinct muscle blocks during early embryonic life � This is best explained by common ancestry = they are all descendants of a
common form e.g. fish (life on earth started in an aquatic environment) - Comparative anatomy � Comparative anatomy is the study of similarities and differences in the structure
of living organisms and can be used to determine evolutionary relatedness � Similarities in structure suggest descent from a common ancestor � Homologous structures: Organisms that have a similar structure, but used in
different way in a different environment - they have the same evolutionary origins � Example - The Pentadactyl limb: five finger-like bones connected to a modified
radius, ulna and shoulder blade (fin of a whale, wing of a bat) - Biochemistry � Biochemistry is the study of chemicals found in cells � Chemicals such as DNA and blood proteins are found in all living things and show
evidence of evolutionary relationships � The degree of similarity between the biochemistry of organisms shows how close
they are genetically i.e. 1.8% difference between humans and chimpanzees, suggesting that they evolved from a common ancestor recently
� Two proteins often studied are: Cytochrome-C (a protein involved in respiration) and Haemoglobin (a blood protein found in only animals
� Example - Humans and chimpanzees: identical sequence of amino acids in their haemoglobin
� Biochemistry has strengthened the idea that change has occurred over time and is not open to subjective opinions, producing objective data (quantitative)
� Biochemical analysis can’t be used on extinct organisms x Explain how Darwin/Wallace’s theory of evolution by natural selection
and isolation accounts for divergent and convergent evolution - Darwin and Wallace proposed that within a population there is genetic variation and
that the individuals who possess inheritable features that are best suited to an environment will survive and reproduce
- Divergent evolution is when individuals of a certain species are subjected to different environments (genetic isolation = geographical barriers) and develop different features (homologous structures) which are better suited to that environment
- Example - The different finches on the islands of the Galapagos - Example - The Pentadactyl limb - Convergent evolution is when individuals of different species are subjected to
similar environments and therefore develop similar features (analogous structures) - Example - Sharks, turtles, dolphins and penguins: found in a water environment, each
possessing streamline bodies, fins and flippers x Plan, choose equipment or resources and perform a first-hand
investigation to model natural selection Aim: To demonstrate how natural selection occurs Risk Assessment: - Do not run with scissors Method: 1. Pretend that one person in your group is a bird who eats worms 2. Count out 50 red and 50 green ‘worms’ (toothpicks) 3. Use the metre ruler, string and scissors to mark out a 1m x 1m square on the
concrete 4. Randomly scatter the ‘worms’ in the square on the concrete, making sure the ‘bird’ is
not watching 5. The ‘bird’ in your group has 30 seconds to pick up (‘eat’) as many ‘worms’ as possible
NOTE: The ‘worms’ must be picked up one at a time 6. Count the number of red and green ‘worms’ caught and record the results 7. Repeat steps 1-5 three times 8. Repeat steps 1-6, however this time put the ‘worms’ on green grass, not on the
concrete Results: - Less green worms were eaten in the grass compared to red worms as they were
more camouflaged - This model compares to natural selection as there is;
1. Variation: Red and green worms 2. Different environments: Concrete and grass
3. Adaptation: The green worms (on the grass) were not eaten as much as the red worms
4. Survive and reproduce: The green worms (on the grass) would survive and reproduce
5. Population increases: The green worm population would increase and the red worms would slowly become extinct
Independent variable: Environment (grass or concrete) Dependent variable: Number of worms eaten Controlled variables: Size of the area, the bird Limitations: In real life the worms would have to be swallowed, not just put in a cup. Also the scattering of ‘worms’ is not necessarily random as well as the selection of the ‘worms’ by the ‘bird’ x Analyse information from secondary sources to prepare a case study to
show how an environmental change can lead to changes in a species - Peppered moths are either pale or dark in colour - Unpolluted area = the pale moths are well camouflaged by the lichen on the surrounding
trees and darker moths are much easier to see - The birds within the ecosystem prey on the darker moths as they are much more visible =
the paler moths occupying the ecosystem reproduce, passing on the desirable feature - Industrial pollution = trees are darker in colour - Darker moths have a greater camouflage compared to the paler moths = paler moths are
picked off by the bird population - Darker moths through years of natural selection have a higher survival rate in a polluted
area x Perform a first-hand investigation or gather information from secondary
sources (including photographs/diagrams/models) to observe, analyse and compare the structure of a range of vertebrate forelimbs
Variation Significance Examples Small bones with many joints
Allow flexibility and ease of movement, act as a good shock absorber
Rabbit, frog
Solid bones that are fused
Efficient support of body weight; confers strength
Increased carpal and tarsal bones and lifting of hind end of heel off the ground
Animal walks on digits which increases stride
Dog, rabbit
x Use available evidence to analyse, using a named example, how advances
in technology have changed scientific thinking about evolutionary relationships
- DNA hybridisation is used to identify the similarities between two different organisms by comparing their DNA
- The process of DNA hybridisation is outlined below; � 2 strands of DNA are collected. One from one species, the other from another � These 2 strands are heated, causing the strands to separate � One strand from each organism is then combined to form a hybrid. Not all of the
bases in each sequence will match up - Pairing of the DNA strands depends on the similarities of the organisms - Organisms are said to have come from a recent ancestor if their sequence is highly
similar - Conversely if the sequence has a low degree of pairing the organisms are said to be
unalike - DNA hybridisation has changed scientific thinking, enabling scientists to compare
organisms genetically - Scientists can determine whether a species recently diverged from a common
ancestor or diverged from a common ancestor a long time ago x Analyse information from secondary sources on the historical
development of theories of evolution and use available evidence to assess social and political influences on these developments
- The historical development of theories of evolution � Prior to the 18th Century: A strong belief in Creationism - common belief that God
created all creatures the way they are now � 1735: Carolus Linnaeus published a classification system - humans are grouped
with apes - idea is strongly resisted � Late 18th Century: Erasmus Darwin (Charles Darwin’s grandfather) proposed that
all life originated from a single source � 1809: Jean-Baptiste de Lamarck put forward the first theory of evolution -
variation in species was caused by the use or disuse of body parts, passed onto offspring
� 1859: Charles Darwin published On the Origins of Species by Means of Natural Selection - first scientifically acceptable explanation for the gradual change in species over time. He put forward the idea that organisms with favourable variations reproduce and pass them on. Over time favourable variations become common in the species, and they are fit to survive
� 1864: Alfred Wallace publishes an essay on evolution, titled On the Tendency of Varieties to Depart Indefinitely from the Original Type. Very similar to Darwin’s work, but less credited
� 1866: Austrian monk, Gregor Mendel, published his work on genetics, based on his work on some 30,000 pea plants. He is widely ignored
- Social and political influences � Influences prior to the publishing of evolutionary theory:
Christianity was a very dominant force during the time of Charles Darwin Creationism was widely accepted, as a religious and a scientific concept Darwin knew what a huge impact his knowledge would make on the world
when he released it, so he withheld his theory for 25 years It was only when he felt the social and political climate was right, did he publish
his information He chose to publish it during a time of great societal change i.e. the Industrial
Revolution and a time when the power of the Church was weak Also, Wallace’s willingness to propose his own version of evolution prompted
Darwin to finally publish his papers � Influences of evolutionary theory on society:
Darwin’s theory caused public outrage at the time. Great debates were fought out by evolutionists and creationists (e.g. between Thomas Huxley and Bishop Samuel Wilberforce)
Darwin was also blamed for many catastrophes in history, as people continued to wrongly apply the ‘Survival of the Fittest’ to normal life
Darwin has been blamed for the destruction of religion and the rise of atheism, fascism, communism and even the Second World War, as people like Karl Marx base their philosophies on The Origin of Species
2. Gregor Mendel’s experiments helped advance our knowledge of the inheritance of characteristics
x Outline the experiments carried out by Gregor Mendel - Began work in 1858, published his results in 1866 - Formulated the principles of genetics by careful and methodical experimentation
with garden peas - Chose garden peas as they were easy to grow, produced new generations quickly and
had distinguishable traits that show clear dominance and recessive - Worked with self-fertilisation plants which produced all offspring identical to the
parent - Able to strictly control the fertilisation process by placing a bag over the flowers to
make sure that the pollen from the stamens landed on the stigma of the same flower - Used mathematics to rigorously analyse his results (statistically analysed) - Method: � Self-fertilised two true-breeding plants for one characteristic e.g. a tall plant with a
short plant (P₁ parent generation) � Offspring produced were called the F₁ generation and were then self-fertilised to
produce a second fertilisation, F₂ - Found that only the dominant factor appeared in F₁
- The recessive factor appeared in F₂ in a 3:1 (dominant:recessive) relationship x Describe the aspects of the experimental techniques used by Mendel that
led to his success - Large sample size - Methodical experimentation - Controlled fertilisation - Use of mathematics to statistically analyse his work - Brilliant deductions/interpretations x Describe the outcomes of monohybrid crosses involving simple
dominance using Mendel’s explanations - Monohybrid crosses (punnett squares) are crosses which involve only one specific
characteristic e.g. eye colour, hair colour, or in Mendel’s case the height of pea plants - Information to produce a cross includes whether or not the cross is between
homozygous and heterozygous pairs and whether or not the characteristic is dominant or recessive
- Mendel crossed a homozygous tall (TT) pea plant with a homozygous short plant (tt) - Tall allele is dominant = first generation (F1) of plants were all tall, all would carry
the short allele - Second generation (F2) with the short allele expressed in a ratio of 3:1 (tall:short) - Simple monohybrid crosses help scientists determine the dominance of a gene as
well as hypothesise what outcome could be between certain crosses involving certain characteristics
T T T t
t Tt Tt T TT Tt
t Tt Tt t Tt tt
x Distinguish between homozygous and heterozygous genotypes in monohybrid crosses
Homozygous Genotypes Heterozygous Genotypes � Homozygous alleles are either
dominant or recessive � Dominant homozygous alleles are
always expressed as capital letters (AA)
� Recessive homozygous alleles are always expressed as lower case letters (aa)
� The letters used to illustrate the specific characteristic are known as the genotypes
� Heterozygous genotypes contain different alleles that express different characteristics
� Heterozygous alleles always contain a dominant gene and a recessive gene
� Heterozygous alleles are always expressed as a capital and a lower case letter (Aa)
� The letters used to illustrate the specific characteristic are known as the genotypes
x Distinguish between the term allele and gene, using examples
- A gene is a section of DNA coding for polypeptides which when expressed is the phenotype of an organism e.g. gene coding for hairline in humans
- An allele is the alternative code for a gene. They occur in pairs (same alleles = homozygous, different alleles = heterozygous) e.g. alleles for hairline in humans are straight (H) and widows peak (h) NOTE: when referring to alleles - the code must be referred to and not just the phenotype
x Explain the relationship between dominant and recessive alleles and phenotype using examples
- Dominant and recessive alleles can be linked to the phenotype of an offspring - Recessive alleles are expressed when there is an absence of a dominant gene - The phenotype of the offspring is the actual physical characteristic that is being
expressed - Example - a dominant black haired person (BB) produces offspring with a recessive
blonde hair person (bb) B B
b Bb Bb b Bb Bb
Therefore there is 100% that the offspring will have the phenotype of black hair
x Outline the reasons why the importance of Mendel’s work was not recognised after it was published
- He was an Austrian monk, didn’t socialise with scientists - Wasn’t high profile - Required sponsorship, he didn’t have that - Not a member of the scientific community - Presented his paper to a small group of people, so his work didn’t come out - People didn’t understand his work because of the mathematics involved - He was shy, didn’t push his ideas - Scientific community was so focused on evolution, other works were ignored
x Perform an investigation to construct pedigrees or family trees, trace the inheritance of selected characteristics and discuss their current use
Aim: To construct pedigrees or family trees by tracing the inheritance of a selected characteristic Method: 1. Select at least 10 members of your family covering three generations 2. Select ONE characteristic that show variation 3. Construct a family tree 4. Shade the symbols for ONE of the variations 5. Draw a key 6. Determine if the characteristic is recessive or dominant
Results: Right handed = dominant, left handed = recessive NOTE: Problems associated = All of my family lives overseas and so gathering information was difficult. Usefulness = Pedigrees can be used to help breed out a genetic problem e.g. hip dysplasia in grey hounds x Solve problems involving monohybrid crosses using Punnett squares or
other appropriate techniques NOTE: see end of notes x Process information from secondary sources to describe an example of
hybridisation within a species and explain the purpose of this hybridisation
Labradoodle: hypoallergenic and friendly Poodle - Hypo-allergenic fur
3. Chromosomal structure provides the key to inheritance x Outline the roles of Sutton and Boveri in identifying the importance of
chromosomes - Walton Sutton � American cytologist � Studied meiosis in grasshoppers � Concluded that chromosomes were the carriers of heredity units and behaved in
the same manner as Mendel’s ‘factors of inheritance’ (genes) � Chromosomes arrange themselves independently along the middle of the cell just
before it divides - Theodor Boveri � German biologist and cytologist � Carried out experiments on sea urchin eggs, studying the behaviour of nucleus and
chromosomes during meiosis and after fertilisation � Found that chromosomes are the carriers of heredity � Deduced that there must be many ‘factors’ (now known as genes) on one
chromosome Before Sutton and Boveri’s
work After Sutton and Boveri’s work
Where in the cells are heredity factors found?
- Cytoplasm and nucleus - Nucleus only
What material stores the heredity information?
- Unsure - perhaps proteins - A full set of paired chromosomes, where many heredity factors are carried on each chromosome
How are inherited factors passed to the next generation?
- Gametes transport ‘factors’ but how or what these factors were was unknown
- Random assortment during meiosis - units of inheritance carried on chromosomes in gametes
Nature of chromosomes
- Chromosomes were believed to disappear and reappear and were all believed to be the same size and shape
- Chromosomes occur in set numbers in pairs in every cell and each pair of chromosomes are the same size and shape
x Describe the chemical nature of chromosomes and genes - Chromosomes are made up of chromatin, which is 60% protein and 40% DNA - A gene is a section of DNA on a chromosome - Genes are protein molecule = carbon, hydrogen, oxygen, nitrogen x Identify that DNA is a double-stranded molecule twisted into a helix with
each strand comprised of a sugar-phosphate backbone and attached bases - adenine (A), thymine (T), cytosine (C) and guanine (G) - connected to a complementary strand by pairing the bases, A-T and G-C
- DNA (deoxyribonucleic acid), double stranded helix - Made up of sub-units called nucleotides = phosphate, sugar, nitrogenous base - Sugar = deoxyribose - There are four different bases; adenine (A), thymine (T), cytosine (C), guanine (G)
Adenine pairs with thymine (A-T) and cytosine with guanine (C-G) � A single DNA strand is made up of a chain of nucleotides (polynucleotide) where
the phosphate and sugar alternate as the backbone of the strand � The bases attach to the sugar � The other strand of DNA attaches to the strand by complementary pairing of the
nitrogenous bases
x Explain the relationship between the structure and behaviour of chromosomes during meiosis and the inheritance of genes
- The alignment of replicated homologous pairs (one maternal and one paternal chromosome in each pair) at the equator of the cell � Crossing over may occur at this stage - the exchange of genetic material between
homologous chromosomes causes the mixing of maternal and paternal genes and the result is an increased number of combinations of genes that may be transmitted by gametes to offspring, thereby increasing genetic variation
- The first meiotic division where homologous pairs are separated (segregation of chromosomes) - one entire chromosome of each pair moves into a daughter cell � Independent assortment = paternal and maternal chromosomes assort
themselves independently of each other, leading to further genetic variation - The second meiotic division where chromatids are pulled apart (does not cause
further variation) - The formation of 4 haploid gametes (one set of chromosomes - 23) which have only
NOTE: Genes that occur on the same chromosome are said to be linked. Crossing over ensures that linked genes on a chromosome can be inherited independently of each other. There are many possible combinations of genes an individual can inherit from a particular parent.
x Explain the role of gamete formation and sexual reproduction in variability of offspring
- Genetic variability refers to the amount by which individuals in a population vary from each other genetically. There are four ways in which this variation can occur: � Crossing over during meiosis: exchange of genes between chromosome pairs =
combinations of alleles of the gametes will vary across cells � Random segregation of chromosomes during meiosis: genes on different
chromosomes sort independently = produces many gene combinations - Both result in gamete variability - different, recombined genetic material � Fertilisation: random union of sex cells, the possibility of many different
combinations of gametes fusing � Mutation (which also applies to asexual reproduction)
x Describe the inheritance of sex-linked genes, and alleles that exhibit co-dominance and explain why these do not produce simple Mendelian ratios
- Sex Linkage � Refers to the inheritance patterns determined by the genes located on the sex
chromosomes (23rd pair) � Female = XX, a recessive allele can only be expressed if present on both X
chromosomes � Male = XY, it only takes one recessive gene from the mother to be expressed in
male offspring � The Y chromosome is much shorter than the X chromosome and contains
characteristics that determine sexual features in males � This means that males carry only one allele for the many genes carried on the X
chromosome, therefore if an allele is recessive, it cannot be hidden by a dominant allele
� Example - haemophilia, H is the dominant, normal allele and h is the recessive, haemophiliac allele
XH Xh
XH Xh
XH XHXH XHXh Xh XHXh XhXh
Y XHY XhY Y XHY XhY Female: - Normal female’s genotype: XHXH - Carrier female’s genotype: XHXh - Haemophiliac female’s genotype: XhXh
Male: - Normal male’s genotype: XHY - Haemophiliac male’s genotype: XhY - The recessive allele therefore appears more often in males than females
� When two alleles are not dominant over each other, they are both expressed � Example - Roan cattle: R = red colour allele, W = white colour allele, RW = red and
white blended (roan)
R R
R W
W RW RW R RR RW
W RW RW W RW WW A cross between a white (WW) and a red (RR) cow: - All offspring RW (Roan = a blend of red and white)
A cross between 2 roan cows: - 1 Red:2 Roan:1 White - 1 RR:2 RW:1 WW
- Therefore, sex-linkage and co-dominance do not produce simple Mendelian ratios - Mendel started with pure breeding parents and interbred the offspring which limited
the genetic pool, causing a steady ratio of plants with certain characteristics - His experiment did not include different situations x Describe the work of Morgan that led to the understanding of sex linkage - Morgan bred fruit flies (Drosophila) for one year - These flies were meant to have red eyes, but he noticed a male with white eyes - He then bred this male with a red-eyed female and all the offspring had red eyes - The F2 generation produced females with all red eyes, half of the males had red eyes
but the other half had white eyes - Morgan then hypothesised that the white-eyed characteristic was sex ‘limited’ and
was located on the X chromosome - Advantages of observing fruit flies; � They have easily observable characteristics as they are only carried on 4 pairs of
chromosomes � They can be bred quickly and easily in the laboratory � Large amounts of offspring are produced with a generation time of 10-12 days
x Explain the relationship between homozygous and heterozygous genotypes and the resulting phenotypes in examples of co-dominance
- In simple dominance cases, if an organism was homozygous dominant then the phenotype would be that of the dominant allele and if the organism was homozygous recessive then the recessive allele would be the phenotype
- In co-dominance, heterozygous organisms would have both alleles expressed and therefore the phenotype would be both alleles
- Example - red and white roan cattle = 1 phenotype of red, white x Outline ways in which the environment may affect the expression of a
gene in an individual - Genes are not the only factor that influences phenotype - The environment can influence the expression of a gene in an individual
- For example, identical twins have exactly the same genetic information so any difference must be a result of the environment
- Specific examples: � Hydrangeas: This flower’s colour is controlled by pigments known as
anthocyanins. These are affected by pH. If the hydrangeas grow in acidic environments, the flowers will be bright blue. In alkaline environments, the flowers are pale-pink or off-white
� Phenylketonuria (PKU): Babies born with PKU cannot make the important enzyme phe-hydroxylase and as a result, cannot metabolise the amino acid phenylalanine (phe) into tyrosine. This is a genetic disorder. If they eat excessive amounts of phe, the babies will become severely mentally disabled but if phe levels are kept low, the babies will grow up healthy
x Process information from secondary sources to construct a model that demonstrates meiosis and the processes of crossing over, segregation of chromosomes and the production of haploid gametes
NOTE: see end of notes x Solve problems involving co-dominance and sex linkage NOTE: see end of notes x Indentify data sources and perform a first-hand investigation to
demonstrate the effect of environment on phenotype Aim: To investigate the affect of heredity and the environment on the phenotype of barley seedlings Hypothesis: The environment will affect the phenotype of the barley seedlings Risk Assessment: - Possible allergic reaction to barley, use forceps and wash your hands afterwards Method: 1. Place a layer of cotton wool in the bottom of each dish, soaked in water (excess
poured off) 2. Use forceps to space ten barley seeds well apart from one another in each dish 3. Put the lids on the dishes. Label the lids and bases of one dish ‘L’ and the other ‘D’ 4. Put ‘L’ in the light (not direct sun). Put ‘D’ in the dark. Keep all other conditions the
same 5. Over the next few days keep the cotton wool moist 6. When at least half the seeds have germinated use a hand lens to count the number of
green albino shoots in each dish 7. Record results every few days Results: - Environment doesn’t affect the albino seedlings (therefore hereditary) - Environment changes normal seeds from green to yellow (if in dark) - In the light, seeds were green unless albino
4. The structure of DNA can be changed and such changes may
be reflected in the phenotype of the affected organism x Describe the process of DNA replication and explain its significance - The process of DNA replication � The parent DNA molecule unzips, at one end, caused by the enzyme helicase � The nucleotide bases are exposed and free-floating DNA nucleotides in the
nucleoplasm attach to the exposed bases, A with T and C with G. This ensures that the replication is exact
� The joining of nucleotides together is catalysed by DNA polymerase - Significance � When a cell divides by mitosis (for growth and repair) it takes with it an exact
copy of the genetic code of that organism � During sexual reproduction, the genetic code is copied and then half of the genetic
information passes into each of the sex cells (meiosis) x Outline, using a simple model, the process by which DNA controls the
production of polypeptides - DNA contains coded information which is usually a set of instructions for joining
amino acids - there are 26 amino acids - DNA is said to control polypeptide synthesis because the particular base sequence
in each DNA molecule determines the order in which amino acids, the building blocks of proteins, link together
- There are 2 stages in polypeptide synthesis: � Transcription - making a RNA copy of a DNA sequence
Promoter: sequence of DNA that starts the process of transcription The DNA unwinds and unzips (by RNA polymerase) to create a template (non-
coding strand of DNA) Free-floating RNA nucleotides attach themselves to the complementary bases
The complementary nucleotide chain that forms, acts as a messenger (mRNA), DNA does not leave the nucleus (too big, too important)
Thymine (T) is replaced by a uracil (U) base, pairing with adenine (A) Codon: smallest unit that can code for an amino acid (triplet of bases) Introns: sections of mRNA that are cut off before leaving the nucleus, before
translation Extrons: the sections that are left of mRNA for translation The mRNA moves out of the nucleus into the cytoplasm (to the ribosomes)
where the message has to be translated in order to make polypeptide chains 1 mRNA = code from 1 gene = 1 polypeptide
� Translation - the process of converting mRNA codon sequences into amino acid sequences Ribosomes are the ‘machinery’ which translates the message (mRNA) by
directing the synthesis of polypeptides The ribosomes move along the mRNA molecule and attach tRNA molecules by
temporarily pairing the bases of the tRNA anticodons with the complementary condons on the mRNA
The amino acid is sliced off the tRNA leaving a growing chain of amino acids, joined by peptide bonds
The tRNA moves back into the cytoplasm where it will be reused The polypeptide chain may be joined by one or more polypeptides and are then
further processed and folded into their correct shape, forming a protein 1 ribosome = 1 polypeptide, however usually more than one ribosome is
translating the same message, thus synthesising multiple copies of the same polypeptide
Æ DNA RNA mRNA tRNA - Sugar = deoxyribose - Double helix - Base = T - Found only in nucleus
- Sugar = ribose - Single stranded - Base = U - Found in nucleus and cytoplasm
- Linear - Many bases
- Specific shape - Three bases only
Both: - Single stranded - Sugar = ribose - U instead of T
x Explain the relationship between proteins and polypeptides - A polypeptide is a single chain of amino acid sub-units linked by peptide bonds - Some proteins consist of just one polypeptide, such as the enzyme pepsin - However, most proteins consist of two or more linked polypeptides - A polypeptide is referred to as a protein when the amino acid chain is twisted or
folded into its specific conformation or shape and becomes fully functional x Explain how mutations in DNA may lead to the generation of new alleles - A mutation is a change in the DNA information (sequence) on the chromosome - Gene mutation produces new alleles of genes in species and so creates new genetic
variation - Large changes in DNA can result in: � Deletion: some of the DNA is lost from the chromosome
� Duplication: a section of the chromosome is copied on the chromosome, the same section of DNA occurs twice
� Inversion: a section breaks off and is reattached the wrong way � Translocation: a piece of DNA from one chromosome breaks off and attaches to a
neighbouring chromosome � Amplification: A section of DNA is repeated many times
- This would result in changes to the information carried by the DNA on the chromosome
- Most mutations are lethal and the cell ultimately dies - If the cell survives it increases the variation within a population of organisms - Mutation can occur during meiosis, consequently the mutation gets passed on from
the parents to the offspring - Therefore it is evident that mutations can lead to the generation of new alleles x Discuss evidence for the mutagenic nature of radiation - Radiation is of two main types; ionising (high energy) radiation, which includes X-
rays and gamma rays, and non-ionising radiation such as ultraviolet light - All of these types of radiation have been shown to increase the rate of gene mutation - Hiroshima (1945): The atomic bomb dropped on Hiroshima during WWII produced
a dramatic increase in cancer deaths and evidence suggests that these cancers were caused by mutations. This is because mutations such as deletions and translocations have been observed in these cancer cells. Also, offspring from people in the area have been born with severe deformities
- The Chernobyl Incident (1986): Research has shown that radiation from this nuclear accident has greatly increased the incidence of mutation-induced cancers in Russia, Ukraine and Belarus
x Explain how an understanding of the source of variation in organisms has provided support for Darwin’s theory of evolution by natural selection
- Darwin knew characteristics were passed from one generation to the next and that variation was essential for natural selection. However, he did not know the cause of this variation
- Mendel showed that new characteristics were inherited as genes (factors) - Boveri and Sutton demonstrated that the behaviour of chromosomes explained how
genes could be inherited - DNA proved to be the material that coded for each gene and is passed from one
generation to the next through the process of meiosis and sexual reproduction - Experiments provide evidence for changes in DNA sequence (mutations) being the
cause of variations and these changes may be inherited - Our modern concept of natural selection now includes the idea that it results in a
gradual change in allele frequencies of a population - When a mutation results in the development of an environmentally favourable
variation, natural selection may lead to evolution x Describe the concept of punctuated equilibrium in evolution and how it
differs from the gradual process proposed by Darwin
- The fossil record suggests that evolution is a sudden and random process but can remain stable for years
- Gould and Eldridge proposed the theory of punctuated equilibrium in 1972 - Punctuated equilibrium suggests that, instead of gradual change, there have been
periods of rapid evolution followed by long periods of stability - Darwin proposed that populations change slowly and gradually over time - However, the fossil record only shows rare occasions where this happens (limited
transitional forms) - If an environment remains stable for many years, it is expected that there is no
change in the organisms living there - It is only when the environment changes that natural selection occurs x Perform a first-hand investigation or process information from
secondary sources to develop a simple model for polypeptide synthesis Aim: To develop a simple model for polypeptide synthesis Equipment: - Pegs - blue (adenine), white (thymine), red (guanine), yellow (cytosine), green
(uracil) - Wool - three colours - Piece of plasticine Method: 1. Construct a single DNA strand from the sequence A T G A A A C T C (coding strand)
using the appropriate coloured pegs and a piece of wool. Attach the complementary ‘base’ pegs to these to form a double stranded molecule
2. ‘Unzip’ the DNA by unclipping the pegs, leaving two single stranded molecules 3. Use the non-coding strand as a template and attach complementary bases (pegs),
using uracil pegs instead of thymine. Thread wool of a different colour through the holes in these pegs to represent a strand of mRNA
4. Use three pieces of coloured wool and thread them through the appropriately coloured pegs to represent the triplets AUG, AAA, CUC. These represent tRNA molecules. Attach a paper label to each tRNA and label them with the appropriate amino acid name
5. Unclip the mRNA molecule from the original strand and stick it onto the plasticine. Attach the three tRNA molecules to the plasticine, one at a time, according to the sequence of bases
6. Attach the amino acids together with tape and remove the pegs and wool. The sequence of amino acids that remains represents a portion of polypeptide
x Analyse information from secondary sources to outline the evidence that
led to Beadle and Tatum’s ‘one gene - one protein’ hypothesis and to explain why this was altered to the ‘one gene - one polypeptide’ hypothesis
- Beadle and Tatum already knew that mutations caused changes in genes and that genes were located on chromosomes
- 1941: Aim was to attempt to alter or inactivate specific genes in the bread mould Neurospora crassa and to observe whether this produced any changes in the organism’s cells
- Neurospora: very simple organism - rapid life cycle, one pair of dissimilar chromosomes (not homologous) = any mutation would be expressed
- Exposed a sample of Neurospora spores to X-rays and then crossed the resulting mutant moulds with non-irradiated organisms
- Some of the resulting spores would not grow without the addition of the amino acid arginine, normal spores appeared to grow quite well with the minimum nutrients provided
- Isolated four strains of arginine-dependent moulds - They knew that arginine needs several enzymes to be made and they found that each
of the four strains was found not to produce one of these enzymes required for arginine synthesis
- Concluded that for each defective enzyme there was one gene on one specific area of a chromosome that had been mutated by irradiation, led to their ‘one gene-one protein’ hypothesis
- Proposed that each gene contained the information to produce a single enzyme and since enzymes control the chemical reactions within a cell, genes must therefore indirectly control growth and metabolism
- Changed to ‘one gene-one polypeptide’ theory because some proteins are made of more than one polypeptide chain
Æ Mutant No amino acid added
Arginine added
Citrulline added
Ornithine added
1 - + + + 2 - + + - 3 - + - -
- no growth + growth
x Process information to construct a flow chart that shows that changes in DNA sequences can result in changes in cell activity
NOTE: see end of notes x Process and analyse information from secondary sources to explain a
modern example of ‘natural’ selection - Peppered moths are either pale or dark in colour - Unpolluted area = the pale moths are well camouflaged by the lichen on the surrounding
trees and darker moths are much easier to see - The birds within the ecosystem prey on the darker moths as they are much more visible =
the paler moths occupying the ecosystem reproduce, passing on the desirable feature - Industrial pollution = trees are darker in colour - Darker moths have a greater camouflage compared to the paler moths = paler moths are
picked off by the bird population - Darker moths through years of natural selection have a higher survival rate in a polluted
area x Process information from secondary sources to describe and analyse the
relative importance of the work of... in determining the structure of DNA and the impact of the quality of collaboration and communication on their scientific research
- James Watson � Worked with Crick � Suggested the helical structure of DNA, obtained from Franklin’s work � The pairing of bases (adenine + guanine, thymine + cytosine), based the
information that adenine also equalled guanine and thymine always equalled cytosine
� Obtained this information from Erwin Chargaff, who used chromatographic separation techniques
- Francis Crick � Worked with Watson � Went on to research how the message contained within DNA is translated into
action in the cell - Rosalind Franklin � Expert in the field of X-ray crystallography, applied her techniques onto fibres of
DNA � Created Photo 51, one of the clearest images of DNA from that time
- Maurice Wilkins � Researched the structure of large molecules � Most likely gave Watson and Crick Photo 51 (without Franklin’s permission)
- Although Watson and Crick closely collaborated with each other, and were able to produce good results together, Wilkins and Franklin (who worked in the same lab) did not have a good relationship
- Their lack of communication with each other, together with Wilkins and other males’ patronising attitude towards Franklin significantly slowed down progress on determining the structure of DNA
- Had all these scientists respected each other and decided to work together, their task would have been completed earlier
- Rosalind Franklin was not provided recognition for her work on DNA when Crick, Watson and Wilkins were given the Nobel Prize
5. Current reproductive technologies and genetic engineering
have the potential to alter the path of evolution x Indentify how the following current reproductive techniques may alter
the genetic composition of a population - Artificial insemination � The injection of sperm into the vagina or cervix, without sexual intercourse � Sperm is collected from a male stud e.g. a champion horse, bull or sheep and then
frozen � Males with especially desirable characteristics may provide sperm for many
females � Desirable characteristics may include; horses: speed, cows: meat, sheep: wool etc. � Can also be used as a method of overcoming human infertility
IVF - where the sperm and ovum are mixed in a nutrient medium outside the woman’s body and then transferred to the woman’s uterus
GIFT - sperm is introduced into the woman’s fallopian tube so that fertilisation occurs naturally. This method is sometimes used due to a couple’s religious beliefs
� Disadvantages: possible diseases are passed on, unfavourable characteristics passed on
� Would alter the genetic composition of a population because male sperm is used for many females and all the desirable characteristics would continue to be passed on
- Artificial pollination � The removal of pollen from one plant that has desirable characteristics and
placing it in the stigma of another flower � Mendel used artificial pollination in his pea plant experiments � Plant geneticists have used the technique to produce a wide range of fruits,
- Cloning � Reproduction of genetically identical offspring � Taking of cuttings from a parent stock and planting them (for plants) � Cloning of mammals has been difficult = Dolly (first cloned mammal) 1998 � Advantage: cloning of desirable features, disadvantage: change in environment =
population dies x Outline the processes used to produce transgenic species and include
examples of this process and reasons for its use - Transgenic species are organisms which have had genetic material from a different
species transferred into their chromosomes - That is, genes from one species have been taken and transferred into another - The introduced gene instructs the transgenic organism to produce the desired trait
or products - This trait may be passed onto future generations - Processes Used to Produce Transgenic Species
1. A useful gene, and the chromosome it is on, is identified 2. The gene is ‘isolated’ or cut-out of its DNA strand 3. Separate DNA sequences for regulation may have to be added to ensure the gene
will work 4. The gene is inserted into the cell of another organism. Sometimes a vector (carrier
of a substance from one species to another) is used to do this - Reasons For Using These Processes � These processes enable scientists to combine the qualities of different organisms � Increase the resistance of plants or animals to diseases, pests or extreme
environmental conditions � For medicines and vaccines and to study human diseases � To improve productivity of crops, pastures and animals � To improve the quality of food and efficiency of food processing
x Discuss the potential impact of the use of reproduction technologies on the genetic diversity of species using a named plant and animal example that have been genetically altered
- The main fear behind the use of genetic and reproductive breeding techniques on organisms is that the natural diversity and variation within a population is decreased
- E.g. cotton plants - the main crop being grown all over the world is BT cotton - As more and more farmers shift from natural cotton to BT cotton, there are many
disadvantages: � Many natural varieties of cotton will be lost � The species itself becomes vulnerable to extinction. If all cotton grown all over the
world is BT, and a disease appears, that kills specifically BT cotton, than there is a risk of cotton becoming an extinct organism
� A lack of variation is a major risk factor in extinction of a species x Process information from secondary sources to describe a methodology
used in cloning - A body cell taken from a donor ewe, placed in a low nutrient culture (starves the cell,
- Unfertilised egg is taken from another ewe (black faced), nucleus with its DNA is sucked out
- The two cells are placed next to one another, given an electric pulse (causing cell division to begin)
- The resulting embryo is implanted in the uterus of another ewe x Analyse information from secondary sources to identify examples of the
use of transgenic species and use available evidence to debate the ethical issues arising from the development and use of transgenic species
- Examples of the Use of Transgenic Species � BT Crops: BT is a bacterium that naturally produces chemicals that kills many
insects. The chemicals are specific to many pests and do not kill other insects. Genetically modified crops have had the gene of BT pesticide inserted into them. They produce their own BT chemicals, and no longer need to be sprayed
� Cold Strawberries: A gene from a type of salmon that allows it to survive cold temperatures has been isolated, and inserted into a strain of strawberry. This strawberry can survive and grow in cold temperatures
� Bacterial Insulin: Diabetics previously obtained their insulin from animals (mainly pigs). The gene for insulin production, taken from the human pancreas, was placed in to the DNA of a bacterium. This now provides mass production of insulin
- Ethical Issues � These technologies help treat diseases and increase food production � Should we be tampering with nature in this way? � Is it right to change living organisms for commercial gain? � Transgenic species disrupt evolutionary relationships between organisms � If a transgenic species was released into the natural environment, it could out-
compete the natural organisms � Health-risks and side effects with eating GM foods
