Blueprint of Life – Syllabus1. Evidence of evolution suggests that the mechanisms of inheritance,

accompanied by selection, allow change over many generations.DP1 “outline the impact on the evolution of plants and animals of:”

changes in physical conditions in the environment changes in chemical conditions in the environment competition for resources

Changes in physical conditions in the environment These include natural conditions, such as temperature and the availability of

water. The Australia landmass has become drier over time and this has lead to

changes in the species of kangaroos that are present today. Approximately 25 million years ago, Australia was considerably wetter than today with large areas of rainforest. During this time, kangaroos were small and omnivorous, with unspecialised teeth, eating a variety of foods from the forest floor. Food was nutritious and abundant; there was no need for specialised grinding teeth.

As Australia became more arid and grass became the dominant vegetation in some areas, environmental selective pressure resulted in larger kangaroos favouring teeth suitable for grass. These teeth, high-crested molars, efficiently grind low-nutrition grass into a more easily digestible paste. Slicing pre-molars are of little use and so became much reduced from the ancestral kangaroos.

Changes in chemical conditions in the environment Chemicals that can affect the evolution of species include salts and elements,

such as iron. For example, many parts of Australia have soils that have a high salinity. There are a range of salt tolerant plants that have evolved to inhabit those areas. The animals that feed from these plants have also evolved to inhabit those areas.

The sheep blowfly, Lucilia cuprina, is a major problem to the Australian sheep industry. It stresses, weakens and can be lethal to sheep when larvae, laid by females, burrows into wounds and wet wool. Chemicals, such as dieldrin and organophosphates, have been used extensively to control the blowfly. However, genetic resistance has occurred within the fly population that has made these chemicals ineffective. Withholding a particular insecticide for a time allowed the resistance of this particular blowfly population to drop. Continued use of the insecticide has resulted in the mutation of a modifier gene that increases and maintains the resistance. Thus, the insecticides can never be effective again, regardless of the number of blowfly generations that pass.

Competition for resources This occurs within a species and between species. If a new species is

introduced into an area then the competition may lead to different species using different resources.

Resources can include food, space or mates. If populations that live in the same area could specialise on slightly different resources or breed at different times, they would avoid direct competition.

Some species of fruit fly have evolved into different species with each confined to a different type of fruit tree. This is possible if there are different flowering and fruiting times on each tree type suited for different breeding cycles in the fruit flies. Eventually, two distinct species can result.

DP2 “describe, using specific examples, how the theory of evolution is supported by the following areas of study:”Palaeontology

The fossil record provides a time line of evolution of life engraved in the order in which the fossils appear in rock layers. Some parts of the fossil record show a gradual change in life forms over millions of years.

Of particular interest are transitional fossils that have characteristics belonging to ancestral and descendant groups. The most famous transitional form is Archaeopteryx. This is a fossil first thought to be a therapsid reptile. Its reptilian features include teeth and a reptilian-like skeleton. However, Archaeopteryx also had feathers and a wishbone sternum used to attach flight muscles. This provides evidence of an evolutionary pathway from dinosaurs to birds.

Biogeography Charles Darwin and Alfred Russell Wallace both observed the distribution of

species into different biogeographic regions and saw this as major evidence to support the theory of evolution. They argued that animals in different regions had come from ancestors in that region and had adapted over time to the conditions there. Special Creation, the prevailing religious-based explanation of the time, did not explain why islands with similar conditions did not contain the same flora and fauna. Darwin proposed that migration and evolution were much more satisfactory explanations for the unique flora found in places such as Australia.

Comparative embryology There is an obvious similarity between embryos of fish, amphibians, reptiles,

birds and mammals. A comparison of embryos of vertebrates shows that all have gill slits, even though they do not remain later in life, except in fish. This indicates a fundamental step that is common to all vertebrates and supports the idea of a common ancestor.

Comparative anatomy Anatomical structures on different organisms that have the same basic plan

but perform different functions are called homologous structures. Homologous structures are evidence for evolution. The structures are shared by related species because they have been inherited in some way from a common ancestor.

An example of an homologous structure is the pentadactyl limb found in amphibians, reptiles, birds and mammals. The basic plan consists of one bone in the upper limb, two in the lower limb leading to five fingers or toes. In bats, the limb is modified to form a wing with the fingers extended and skin stretched between each finger. Whales have within their single paddle-like fin a fully formed pentadactyl limb.

Biochemistry Recent advances in technology have allowed comparison of organisms on a

molecular basis rather than simply comparing structures. This was previously impossible between such distantly related organisms as an orchid and a mouse.

The study of amino acid sequences shows that more closely related species share more common sequences than do unrelated species. Particular evidence has been derived from the amino acid sequence in haemoglobin, showing that humans and rhesus monkeys share all but eight amino acid sequences whereas there are 125 amino acid differences between humans and lampreys. This supports the fossil, embryological and anatomical evidence that humans are more closely related to rhesus monkeys than they are to lampreys.

DP3 “explain how Darwin/Wallace's theory of evolution by natural selection and isolation accounts for divergent evolution and convergent evolution”

Divergent evolution occurs when closely related species experience quite different environments and as a result vastly different characteristics will be selected. The species, over time, will evolve differently and will eventually appear quite different. For example, elephants are large plains-dwelling animals that are closely related to a small guinea pig-like animal called a hyrax. Hyraxes live amongst rocky outcrops on mountains. Comparison of skeletons indicates the close relationship between the two groups.

Convergent evolution occurs when two relatively unrelated species develop similar structures, physiology or behaviours in response to similar selective pressures from similar environments. For example, dolphins (mammals) and sharks (cartilaginous fish) have evolved a streamlined body shape and fins that enable them to move efficiently through their aquatic environment, yet they are only remotely related as vertebrates. Communal social behaviour has developed independently in ants, termites and bees.

SC DP1 “plan, choose equipment or resources and perform a first-hand investigation to model natural selection”

Stick birdToothpicks are mixed and scattered randomly over a measured grassed area. Stick birds (students) are later brought to that area and remain outside a 'fence'. They are told to prey on the 'worms' in the field (collect as many toothpicks as they can) in a given time. After 3 minutes, the 'stick-birds' are driven from the field by the 'farmer' (teacher). They escape back to the classroom.Tally and compare the numbers of green and cream toothpicks recovered. Calculate percentages recovered of each colour.

SC DP2 “analyse information from secondary sources to prepare a case study to show how an environmental change can lead to changes in a species”Starting information: Possible case studies of changes in a species

Changes in physical conditions in the environmentThe teeth of kangaroos have evolved in response to changes in physical conditions in Australia over the last 25 million years.

Changes in chemical conditionsChemicals, such as dieldrin and organophosphates, have been used extensively to control the sheep blowfly, Lucilia cuprina. Genetic resistance has occurred within the fly population in response to these chemicals.

Competition for resourcesSome species of fruit fly have evolved into different species with each confined to a different type of fruit tree.

SC DP3 “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”

Perform a first-hand investigation by observing a range of vertebrate forelimbs to compare their structures. Use at least three different types of vertebrates.

SC DP4 “use available evidence to analyse, using a named example, how advances in technology have changed scientific thinking about evolutionary relationships”

Until the 1950s, the relationships between organisms were worked out by similarities in anatomical features. At this time, it became possible to analyse protein sequence data and DNA sequence data. Proteins, such as haemoglobin, could now be compared and similarities worked out based on biochemical similarity. If the rate of change is approximated, it is possible to work out a molecular clock that estimates the time since two organisms shared a common ancestor.

SC DP5 “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”By the beginning of the 19th century, a great deal of evidence was available to the scientific community that supported evolution. What was missing was a plausible mechanism to explain how evolution was occurring. Charles Darwin and Alfred Wallace independently arrived at evolution as a result of natural selection. Darwin gathered evidence after sailing on the HMS Beagle to South America and the Galapagos Islands. By the early 1840s, he had documented the main points of his theory.

Wallace was a British naturalist working in Indonesia in the mid-1850s. In 1858, Wallace sent a copy of his work to Darwin. Darwin's colleagues encouraged him to publish The Origin of Species at the same time and so receive the credit for his years of work and insight. The Origin of Species included overwhelming evidence to support Darwin's conclusions. Even though the Darwin/Wallace theory of natural selection caused a furore amongst Victorian society in England when published, scientific thinking was gaining respectability and becoming an important mechanism for change.

The theory of evolution has encountered opposition since it was first introduced. This is because it can be seen as a threat to religious and social beliefs.

2. Gregor Mendel’s experiments helped advance our knowledge of the inheritance of characteristics.

DP1 “outline the experiments carried out by Gregor Mendel”

Genetics is the study of heredity. Heredity is the transfer of characteristics from one generation to the next. Its origins can be attributed to Gregor Mendel. Mendel was an Austrian monk born 1822. He studied the inheritance of characteristics in pea plants.He bred two groups of pea plants, over many generations until the offspring showed no variation from the parents.

DP2 “describe the aspects of the experimental techniques used by Mendel that led to his success”

He bred two groups of pea plants, over many generations until the offspring showed no variation from the parents. This ensured he had pure-breeding plants. This group became known as the P generation.He crossed these two groups by manually transferring pollen grains from one flower to another. He prevented self-pollination by removing the stamens of one pea plant. The offspring became known as the F1 generation(first filial generation). Mendel then allowed the F1 generation to interbreed to obtain the F2 generation.

Why was he Successful?Mendel designed his experiments in such away to ensure successful accurate results.

1. He studied a large number of characteristics in the plants.(Form of repetition/reliability)

2. He carried out a large number of crossed.3. He used pure-breeding lines. (Form of accuracy)4. He made exact counts of characteristics. (Form of accuracy)

He studied separate identifiable characteristics that occurred in pairs.

DP4 “distinguish between homozygous and heterozygous genotypes in monohybrid crosses”

When both alleles are the same e.g. BB (both dominant) this is called homozygousWhen the alleles are different not carrying the same information e.g. Bb this is called heterozygous.

BB = homozygous dominantBb = heterozygousbb = homozygous recessive

DP5 “distinguish between the terms allele and gene, using examples”Hair colour is gene, brown is the allele.

DP6 “explain the relationship between dominant and recessive alleles and phenotype using examples”

Dominant allele means it will show through in the persons physical appearanceRecessive allele will turn up only if no dominant allele is present.Dominant alleles are always shown as a capital letter e.g. B = blackRecessive alleles are always shown as a lower case letter e.g. b = blondeGenotype – This is a persons genetic makeup (use letters big B, little b)Phenotype – This is your physical appearance (physical description 50% of babies will have brown hair) If dominant will show through, if not dominant it will not show through unless there is 2 recessive alleles.

DP7 “outline the reasons why the importance of Mendel’s work was not recognized until some time after it was published”Mendel Ignored:- lack of formal education/scientific training- lack of public understanding- isolated- timing coincided with Darwin (was overshadowed by evolution)- publication (published in a very small scientific journal with very small

audience)

SC DP1 “perform an investigation to construct pedigrees or family trees, trace the inheritance of selected characteristics and discuss their current use”A pedigree is a family tree showing a line of descent. It can be used to trace the occurrence of inherited traits in parents and offspring through a number of generations.By convention, circles represent females and squares, males. A line between a square and a circle represents a union and a line down indicates offspring from the union.Filled in symbols represent individuals displaying the phenotype being studied. For example:

Pedigrees are valuable tools in genetic counselling. It allows a pattern of inheritance to be traced throughout generations of a family. This can allow identification of the genetic disease and advice can be made available on the probability of a couple having an affected child. Cystic fibrosis is an example of a recessive genetic disease. Huntington's chorea is an example of a dominant genetic disease.

SC DP2 “solve problems involving monohybrid crosses using Punnett squares or other appropriate techniques”

A monohybrid cross involves the inheritance of one characteristic. All problems apply Mendel's basic laws of inheritance. The following is typical of a problem that uses Punnett squares to solve problems involving monohybrid crosses.

SC DP3 “process information from secondary sources to describe an example of hybridisation within a species and explain the purpose of this hybridization”

Hybridisation means the breeding of two different types of plants or animals. For example, a mule is the result of the union between a horse and a donkey, two different species. The resulting animal has desirable characteristics from both parents but all mules are sterile and cannot produce any offspring. Hybridisation also occurs between different varieties or breeds within a species, such as dog, cattle or sheep breeds. Many, probably most agricultural animals and plants are the result of hybridisation. This results in offspring with desirable characteristics e.g. cross breeding cattle to produce better meat or to be tick resistant and Triticale a grain that is a cross between wheat and rye, two different species. Hybridisation is a good way of producing new commercial plants and animals.

3. Chromosomal structure provides the key to inheritance.

DP1 “outline the roles of Sutton and Boveri in identifying the importance of chromosomes”Boveri and Sea UrchinsBetwenn 1896 and 1904, he carried out experiments on sea urchin eggs, studying the behavior of the cell nucleus and chromosomes during meiosis and after fertilization. Sea urchin eggs were ideally suited for study because they could be easily fertilized in a laboratory and have a quick (48 hour) time frame for larval development.Boveri's findingsIt was already known at the time that each species of living organism has a set number of chromosomes and that, during fertilisation, an egg cell and a sperm cell fuse. Boveri's experimental work with sea urchins showed that the nucleus of the egg and sperm each contribute the same amount (50%) of chromosomes to the zygote (fertilised egg), making a connection between chromosomes and heredity.His experiments showed:

when a normal egg and sperm fused, the resulting offspring showed characteristics of both parents

if the nucleus of only one parent was present, the larvae resembled that parent, but showed abnormalities. When an egg, whose nucleus had 'been removed, was fertilised with a sperm, the resulting sea urchin larvae showed characteristics similar to the male parent. However, they were smaller, had only half the normal number of chromosomes and showed some abnormalities.

From this he deduced that:

—a complete set of chromosomes (that is, chromosomes in pairs) is needed for normal development—the inheritance 'factors' are found on chromosomes within the nucleus—that is, chromosomes are the carriers of heredity.Sutton and grasshoppersWalter Sutton (1877-1916), an American cytologist, studied meiosis in cells of grasshoppers (Brachystola magna). In contrast to the eminent Boveri, Sutton was a young, unknown graduate student who produced remarkable and detailed drawings of his findings in cytology. As a result of his observations, he made the connection between the behaviour of chromosomes during meiosis and Mendel's laws of heredity. His independent findings (1902-4), together with those of Boveri (1902), formed the basis of the chromosome theory of inheritance.

Suttons FindingsSutton's observations of meiosis in grasshoppers revealed that: chromosomes occur in distinct pairs, visible during meiosis in grasshopper cells;

one chromosome of each pair is paternal and the other maternal (today termed homologous pairs) and the chromosomes in each pair have the same size and shape

during meiosis (reduction division), the chromosome number of a cell is halved: the chromosomes in each pair of chromosomes separate (just like Mendel's factors segregate—his law of dominance and segregation) and each gamete receives one chromosome from each pair

fertilisation restores the full number of chromosomes in the zygote.

He concluded that chromosomes were the carriers of heredity units and behaved in the same manner as Mendel's 'factors of inheritance' (genes).

In addition, Sutton stated that: Chromosomes arrange themselves independently along the middle of the cell

just before it divides—that is, they assort independently of each other during segregation, like Mendel's factors (evidence for Mendel's law of independent assortment)

Chromosomes are units involved in inheritance. Sutton, like Boveri, also believed that several Mendelian`factors' must be present in one chromosome and could therefore be inherited as a unit. (This'is what we term 'linkage' today. It will be dealt with in more detail on page 173—sex-linkage).

DP2 “describe the chemical nature of chromosomes and genes”

Chromosomes are compact tread-like molecules made up of 40% DNA and 60% histone protein. Chemically each gene is made up of a portion or section of DNA that codes for particular information. DNA consists of sugar phosphate and nitrogen bases arranged in nucleotides.

DP3 “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.”

DP4 “explain the relationship between the structure and behaviour of chromosomes during meiosis and the inheritance of genes”

Chromosomes are made of DNA. Genes are coded within the DNA on the chromosomes. During division each chromosome (which therefore includes the genes) makes a complete copy of itself. The new chromosome is attached to the original chromosome by a centromere. In the initial division of meiosis the homologous chromosomes line up in matching pairs and one of each pair of homologous chromosomes moves into a new cell. Next the duplicated chromosomes separate to single strands resulting in four sex cells that are haploid, (ie contain half the chromosome number of the original cell).

The genes are located on the chromosomes. They are duplicated during the first stage of meiosis and are then randomly assorted depending on which chromosomes from each pair enters which new haploid cell during the first and second division.

DP5 “explain the role of gamete formation and sexual reproduction in variability of offspring”

Gamete formation results in the halving of the chromosome number (n) (diploid to haploid) and sexual reproduction results in combining gametes (haploid to diploid) to produce a new diploid organism (2n). The processes involved in forming this new organism result in variability of the offspring.

Gametes are formed during the process of meiosis. In meiosis there are two stages that lead to variability. These are:

o random segregation of individual chromosomes with treir associated genes ie, different new combinations of the original maternal and paternal chromosomes and

o the process of crossing over where the maternal and paternal chromosomes of each pairmay exchange segments of genes making new combinations of genes on the chromosomes.

In sexual reproduction each female or male cell produces 4 sex cells (gametes) from the process of meiosis. Each of these sex cells is haploid (has half the normal chromosome number) and has a random assortment of genes from the parent. The genes (Mendel's alleles) are separated and the sex cells have a random assortment of dominant and recessive genes. More variability is introduced depending on which sex cells are successful in fertilisation. The resulting embryo has a completely different set of genes from either of the parents.

DP6 “describe the inheritance of sex-linked genes, and genes that exhibit co-dominance and explain why these do not produce simple Mendelian ratios”Mendel was fortunate in his choice of factors as they all showed dominant/recessive characteristics. However, sex-linked genes and genes that are co-dominant do not display the phenotype ratioos predicted by Mendel's laws.

An example of sex-linked inheritance is red-green colour blindness in humans. The gene is carried on the X chromosome and there is no corresponding gene on the Y chromosome. Therefore males need only one allele for colour blindness on the X chromosome while females require two. This results in many more males being colour blind than females because the father would have to be colour blind and the mother either colour blind or be a carrier for colour blindness. As you would expect the sex of offspring to be 50% male and 50% female the occurrence of colour blindness is higher in males than would be expected from a simple pair of dominant and recessive genes. Take the cross between a normal female XN XN and a colour-blind male X n Y.

All offspring have normal sight. But if the female is a carrier for colour blindness and crosses with a normal male then 50 % of the males will be colour blind and none of the females.

Human blood types are another example of co-dominance. Human blood types give different results from Mendelian ratios. When a homozygous male with AA alleles crosses with a homozygous female with BB alleles then all of the offspring will be a different phenotype from the parents (group AB).

DP7 “describe the work of Morgan that led to the understanding of sex linkage”Thomas Hunt Morgan studied the fruit fly, Drosophila melanogaster, in genetic experiments. After a year of breeding flies, looking for new characteristics, Morgan found a male fly with white eyes in his breeding stock. The normal or ‘wild’ eye colour is red. The white-eyed individual was probably a mutant.He mated this white-eyed male with a red-eyed female and all F1 had red eyes, showing that red eyes are dominant over white. When Morgan crossed two of the F1 generation the offspring had a phenotypic ratio of 3 red-eyed offspring : 1 white-eyed offspring. However, the white-eyed trait was only present in the males, with half the males having white eyes and half having red eyes

DP8 “explain the relationship between homozygous and heterozygous genotypes and the resulting phenotypes in examples of co-dominance”In genetic traits that show co-dominant inheritance, heterozygous individuals show both the dominant and recessive trait in their phenotype.

Examples:– AB blood group in humans– Roan cattle (referred to as red alleles if it crossed with a white cattle you get

patched red and white cows, both show through in phenotype)– Andalusian chickens (black feathers crossed with white feathers appears to

be blue, both show through in phenotype)

Give the genotypic ratio of a cross between two roan cattle

Gametes R WR RR RWW RW WW

1 RR : 1 WW : 2 RW Give the phenotypic ratio of the cross between a roan cow and a white bull.

Gametes R WW RW WWW WW WW

1 Roan : 3 White

Give the phenotypes and genotypes of the offspring between 1 pink snapdragon and 1 red snapdragon.

Gametes R WR RR RWR RR RW

Phenotypes are 50% red and 50% pinkGenotypes are 50% RR and 50% RW

DP9 “outline ways in which the environment may affect the expression of a gene in an individual”- The appearance of an individual is not based solely on their genetic information.

The environment of the organism also plays a part.- Hydrangeas are plants that have different flower colour (pink or blue) depending

on the pH of the soil they are grown in. In acid soils (less than pH 5) Hydrangeas are blue. In soils that have a pH greater than 7 Hydrangeas are pink. The pH has an effect on the availability of other ions in the soil and it is these ions that are responsible for the colour change.

Sex Linkage PatternsX-Linked recessive:

All the sons of an affected female will be affected All the daughters of an affected male will be carriers All children of two affected parents will have the trait In a large sample, more males than females will show the trait

X-Linked dominant: A male with the trait passed it onto all of his daughters and none of his sons A female with the trait may pass it onto her daughters and sons Every affected person has at least one person with the trait In a large sample size, there are more affected females than males

SC DP1 “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”Use plasticine or pipe cleaners to model the process of meiosis to demonstrate crossing over, segregation of chromosomes and the production of haploid gametes. Or use prepared slides showing meiosis.SC DP2 “solve problems involving co-dominance and sex linkage”1. A man with haemophilia marries a woman with no family history. What % chance do they have of having a haemophiliac child?

Alleles X XXh XXh XXh

Y XY XY2. A woman who carries the gene for haemophilia marries a man without haemophilia. What % chance of a haemophiliac child?

Alleles X Xh

X XX XXh

Y XY XhY 25% chance of a haemophiliac child.

3. A haemophiliac male marries a carrier female. What % chance of a haemophiliac child?

Alleles X Xh

Xh XXh Xh Xh

Y XY XhY 50% chance of a haemophiliac child

4. A woman with haemophilia marries a normal man. What % chance of a haemophiliac child?

Alleles Xh Xh

X XXh XXh

Y XhY XhY 50% chance of haemophiliac child. If a woman has haemophilia all of her sons

will have it, if a man has haemophilia he has inherited it from Mum.

SC DP3 “identify data sources and perform a first-hand investigation to demonstrate the effect of the environment on phenotype”Studies on identical twins separated at birth are useful to determine how much the phenotype is determined by the environment. Identical twins have the same genotype, so any differences in phenotype could be determined by the environment.

Other studies that are useful are long-term studies on height of individuals. For example, Japanese people who grew up in America on average were taller than Japanese people who grew up in Japan. Better nutrition was responsible for the Japanese people to reach their genetic potential. This has been shown in an increase in the height of the average Japanese person over the last fifty years as nutrition has improved.

4. The structure of DNA can be changed and such changes may be reflected in the phenotype of the affected organism.

DP1 “describe the process of DNA replication and explain its significance”Steps:

1. Double helix unwinds2. The two strands begin to separate3. Free nucleotides attach to the exposed bases (maintaining base pairing rule

A-T, T-A, G-C, C-G)4. Weak hydrogen bonds bands reform between the bases and the strands

begin to ‘re-zip’5. Each DNA molecule re-twists back into the double helix

Significance:Mitosis:It is significant because you do not want any change, you want the new cell to do it’s intended job, whether it be a skin cell, nerve cell etc.Meiosis:Ability to exactly copy information to be passed onto offspring, to make sure they receive the correct phenotypic characteristics.

DP2 “outline, using a simple model, the process by which DNA controls the production of polypeptides”DNA stores genetic information. The sequence of bases determines the sequence of amino acids in protein molecules. The smallest unit that can code for an amino acid is a codon, or triplet of bases. For example, the DNA code CCA codes for an amino acid called glycine. Protein synthesis involves the transcription of the code from DNA to mRNA and then the translation of the code from mRNA to tRNA.The first step in polypeptide synthesis involves the unwinding of the DNA, and the copying of one strand by mRNA. Once the mRNA has the code for the protein, it moves from the nucleus into the cytoplasm.In the cytoplasm the mRNA moves to a ribosome where it binds to the ribosome at the end with a ‘start’ codon. In translation, a tRNA in the cytoplasm moves to the codon on the ribosome. At one end of the tRNA there is an anticodon that matches the codon of the mRNA, and at the other end of the tRNA is an amino acid. Once the first amino acid is attached, the second tRNA brings in its amino acid to attach to the next codon and this slowly builds up the sequence of amino acids.Note: mRNA does not have a T it has a UDNA A T G C C T G A C A T GmRNA U A C G G A C U G U A CtRNA A U G C C U G A C A U GCodon = block of 3Anticodon = Codon but once it is tRNA

DP3 “explain the relationship between proteins and polypeptides”A protein is made up of one or more polypeptides. A polypeptide is made up of a chain of many amino acids.

DP4 “explain how mutations in DNA may lead to the generation of new alleles” Any change in the base sequence in DNA results in changes to the

polypeptides that are produced and is a source of new alleles. To produce changes in alleles, the mutation must occur in the sex cells of the

organism which are then passed on to the next generation.DP5 “discuss evidence for the mutagenic nature of radiation”Evidence for radiation as a mutagen:

Marie Curie- Worked with radioactive substances- Died of cancer

Chernobyl – - Leaking of radioactive waste- Cancer, birth defects

Rosalyn Franklin- Worked with X-Rays- Died of cancer

Hiroshima- Radiation from bombs- Cancers, birth defects

Beadle and Tatum- X-rays bread mould- Mould mutated and was unable to produce a specific enzyme

Skin Cancer- UV radiation- Skin cancer rates

Chemicals:- Agent Orange- Nicotine- Benzene- Asbestos

DP6 “explain how an understanding of the source of variation in organisms has provided support for Darwin’s theory of evolution by natural selection”

One of the foundation pillars for the theory of evolution is the variation that occurs among individual members of a species. The basis of this variation is the genetic makeup of the individuals in a species. It is this variation that selection acts upon. Mutation of DNA provides a source of new variations thus supporting Darwin's theory of evolution.

DP7 “describe the concept of punctuated equilibrium in evolution and how it differs from the gradual process proposed by Darwin”

Punctuated equilibrium differs from Darwin's gradual evolution in that evolution is seen as long periods where there is little change in organisms, followed by a shorter period where there are rapid changes. Evolution is a sudden process rather than slow gradual change. The evidence for this comes from the fossil record where there are mass extinctions of organisms followed by the appearance of new species.

SC DP1 “perform a first-hand investigation or process information from secondary sources to develop a simple model for polypeptide synthesis”

You could choose to perform a first hand investigation using beads and plasticine to model polypeptide synthesis. Include in your model the transfer of information from DNA to messenger RNA (mRNA). You will also need to make a model of transfer RNA and of several amino acids. Alternatively, you could process information from an animation, such as those indicated below. When doing this activity, evaluate the relevance of first-hand and secondary information in relation to the understanding of the process of polypeptide synthesis.

SC DP2 “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 used bread mould to investigate nutritional mutations. Using X-rays, they produced mould that was unable to produce a specific amino acid. The mould was unable to grow unless the amino acid was added. They showed that genes controlled biochemical processes. Their hypothesis was that for each gene there was one enzyme or protein. The enzymes that they studied consisted of one polypeptide but many enzymes consist of chains of polypeptides. Therefore, the hypothesis has been changed to the “one – gene one – polypeptide” hypothesis.

SC DP3 “process information to construct a flow chart that shows that changes in DNA sequences can result in changes in cell activity”

SC DP4 “process and analyse information from secondary sources to explain a modern example of ‘natural’ selection”

Some organisms, such as bacteria and insects, produce large numbers of offspring.

Amongst large numbers of bacteria offspring, some individuals may carry genes that give them resistance to antibiotics. These individuals are then able to survive and reproduce with reduced competition from other members of the same species. Each generation will produce a higher percentage of individuals containing the resistant genes. This has been the story for antibiotics since they were first used. The initial use of an antibiotic results in good protection from bacteria. Over time the chemicals become less and less effective. A case study provides a good example of how natural selection occurs. A similar situation occurs in the resistance of insects to insecticides.

Selecting those individuals that are able to survive and reproduce increases the frequencies of those genes in the population. This is “survival of the fittest” where the fittest are those that have a natural resistance to a selecting factor, which in the case of bacteria described above, is antibiotics.

SC DP5 “process information from secondary sources to describe and analyse the relative importance of the work of:

o James Watsono Francis Cricko Rosalind Franklino Maurice Wilkins

in determining the structure of DNA and the impact of collaboration and communication in scientific research”

James Watson – Worked together with Crick in finding the Double HelixFrancis Crick – Worked together with Watson in finding the Double HelixMaurice Wilkins – Worked together with Franklin with photographs – stole Franklins Photo 51Rosalind Franklin – Worked together with Wilkins with photographsThe communication between Watson/Crick and Wilkins was important because without Wilkins giving them the photograph their timeframe in discovering the double helix would be extremely held back. Also if Franklin and Wilkins were working in the same place and they both knew what each other worked on, so if Wilkins never worked with Franklin, he never would have found the photograph to give to Watson/Crick and they progress would have been delayed.

5. Current reproductive technologies and genetic engineering have the potential to alter the path of evolution.

DP1 “identify how the following current reproductive techniques may alter the genetic composition of a population:”

o artificial inseminationo artificial pollinationo cloning

In the case of all the technologies mentioned, the donor gametes or body cells have been carefully selected for predetermined characteristics – or artificially selected. In most cases, one exemplary donor contributes all the genetic material and this results in uniform offspring. Over generations, genetic variability within the species has been reduced.

DP2 “outline the processes used to produce transgenic species and include examples of this process and reasons for its use”

Transgenic organisms contain a gene (transgene) from another species. This is acheived through recombinant DNA technology. Recombinant DNA technology manipulates DNA by the use of restriction enzymes, ligases and PCR (polymerase chain reaction). Restriction enzymes are used to cut DNA in specific places. These enzymes are also known as gene scissors or gene shears. Different restriction enzymes cut DNA in specific parts. The cut ends are known as 'sticky ends'. Ligases are used to repair and strengthen DNA especially after it has been cut by restriction enzymes. PCR is used to produce many copies of the recombinant DNA formed by the previous processes.

Once the recombinant DNA is produced there are processes used to insert the DNA into the host species. These processes include microinjection, Ti plasmid insertion, gene gun and electroporation.

In microinjection a fine glass needle is used to insert the recombinant DNA into the nucleus of the host cell.

Ti (tumour inducing) plasmid insertion uses a bacterium called Agrobacterium tumefaciens. These bacteria produce crown gall in plants by inserting some of their own DNA into the host DNA causing the plant to produce a gall in which the bacteria live. The ability of the bacteria to insert DNA is used to transfer DNA into the host species.

The gene gun blasts small metal pieces coated with DNA into the nucleus of the host cell.

Electroporation uses electric pulses to create small pores in the nuclear membrane through which DNA is inserted.

Examples of transgenic species are genetically engineered salmon which have the gene coding for the protein, bGH (bovine growth hormone), and potato plants which have a pea gene for lectin inserted.

DP3 “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”

Reproductive technologies, such as cloning, and the engineering of transgenic species have the potential to both increase and decrease genetic diversity. By moving genes from species to species, the genetic diversity is being increased. Crops, such as rice, have been genetically engineered to suit a particular climate and topography, making then resistant to herbicides and pesticides commonly used in a particular region.

Transgenic animals present greater problems with lower success rates so far. One important use is seen to be the preservation of numbers of endangered species. The first cloned endangered mammal was a guar (an endangered wild ox from SE Asia), but unfortunately it did not survive. It is hoped that reproductive technologies such as cloning and sperm and embryo banks can be used to preserve stocks of threatened species.

SC DP1 “process information from secondary sources to describe a methodology used in cloning”

Recently, plants have been cloned using tissue culture propagation. Tissue from the roots is taken and the root cells separated. These cells are then grown (cultured) in a nutrient-rich medium where they become unspecialised. The unspecialised cells are called calluses. After treatment with the appropriate plant hormones, the calluses are able to develop into seedlings, that go on to grow into fully mature plants. These plants are genetically identical to the original ‘parent’ plant. Rare orchids have been cultured and grown in this manner. A more recent example, has been the cloning of tissue from the Wollemi Pine. This rare pine, thought to be extinct but now has been discovered in the Blue Mountains region of NSWand successfully cloned. These cloned offspring are being cultivated in the Royal Botanic Gardens in Sydney and sold to the public for planting in gardens. Thus, the species, which has few numbers in the wild, can be preserved.

In animals, progress in cloning species has not been as rapid. Current techniques require an unfertilised egg to act as a ‘host’ for genetic material from a specialised cell. The donor egg has had its nucleus physically removed, and the nucleus from a cell of the species to be cloned is inserted. An electrical stimulus is used to fuse the nucleus with the egg cell and to stimulate cell division. At a certain stage in cell division, the embryo is introduced into a surrogate mother where it continues its development. When born the clone is genetically identical to the animal that donated the original nucleus. Cloning of animals was first performed with tadpoles by John Gurdon in the 1970’s. The tadpoles did not survive to grow into adult frogs. Dolly the sheep was the first successfully cloned mammal in 1997. Since then, other species have been cloned.

SC DP2 “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”Some ethical issues arising from the development and use of transgenic species

Transgenic organisms are those that have DNA derived from another species incorporated into their genetic complement. This is done by genetic engineering techniques. Both plants and animals have been genetically modified to create ‘improved’ strains of a particular species.

The following are two examples:Genetically engineered salmon: The gene coding for the protein, bGH (bovine growth hormone), is incorporated into the genes of salmon.

Outcome – larger, faster growing fish Evaluation – Possible farmed source of fish as food. However, the fish are

kept in ponds that offer no escape to the wild because there is much concern that they will upset or destroy natural ecosystems.

Potato plants:A pea gene for lectin has been incorporated into potato plants.

Outcome – protection against insect attack. Lectin is a protein which interferes with digestion in insects. It is termed an ‘antifeedant’.

Evaluation – As potatoes are a staple food source for many populations throughout the world, it is important to maintain and increase production. Protection against insect attack improves the success of growing potatoes. Concerns exist about controlling the ‘escape’ of these transgenic potatoes into the wild as the technology is only recent and long-term impacts on the environment have yet to be observed or evaluated.