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72 Cards in this Set
- Front
- Back
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List examples of physical changes in the environment that can impact the evolution of plants and animals
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Temperature, water availability,
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List examples of chemical changes in the environment that can impact the evolution of plants and animals
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Salts and elements e..g salinity
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List and define examples of areas of study that support the theory of evolution
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- Paleontology: study of fossils
- Biogeography: study of geographical distribution of organisms (both extant and extinct) - Comparative embryology: comparison of embryos of different species - Comparative anatomy: study of similarities and differences of structure - Biochemistry: DNA hybridization, DNA sequencing |
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How is evolution supported by Paleontology (with example)
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Fossils show a sequence of life from oldest (at the bottom of rock strata) to to youngest (at the top). This shows that some species evolved over time while some became extinct.
Example: Archaeoptryx - the fossil remains of an organism between birds an reptiles. Reptilianfeatures --> teeth and long tail. Bird-like features --> feathers and a wishbone for attachment of flight muscles. |
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How is evolution supported by Biogeography ( + example)
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Many species show close relationships even though they are in different regions. This shows they shared a common ancestor when the continents were joined. Organisms that were separated later were more genetically similar.
e.g. The current distribution of flightless birds suggests that they originated from a common ancestor. Different populations evolved separately in southern continents as they drifted apart. There are none in the northern continents |
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How is evolution supported by Comparative embryology (+ example)
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Similarities in embryo structure suggest a common ancestor.
E.g. all vertebrate embryos have gill slits. Some fish and amphibians develop the gills, but they disappear in others |
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How is evolution supported by Comparative anatomy (+ example)
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Similarities in structure suggest common ancestor. Differences are evidence change over time.
e.g. Thefour limbs of vertebrates have the same basic arrangement of bones which is thepentadactyl limb but there are modifications according to the function of thatlimb. |
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How is evolution supported by Biochemistry (+ example)
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All living things share DNA - suggests common ancestor.
The more distantly related, the more chemically different the organisms. E.g. DNAsequencing showed us that the human and chimp were more closely related to eachother than either was to the gorilla. |
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What is the Darwin/Wallace theory?
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Characteristics favourable to the reproduction and survivalof organisms in their environment will be selected for, and over time, newspecies will appear in response to environmental changes.
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What is adaptive radiation?`
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Theevolutionary variation in species that evolved from a common ancestor as aresult of migration and isolation. Radiation refers to ‘spread out’. The Darwin/Wallace theory of natural selection provides a mechanism for this.
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What is Divergent evolution?
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Closely related species experience different environments so vastly differentcharacteristics will be selected. Overtime species evolve differently and gradually look more different.
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What is Convergent evolution?
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Two relativelyunrelated species develop similar structures, physiology or behaviors inresponse to similar selective pressures from similar environments.
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Briefly describe how you could model natural selection
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- Red and Green toothpicks
- Scatter on grass - Gather toothpicks under time limit - Count how many red and how many green were picked up - There should be more red |
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Describe an example of how an environmental change can lead to changes in a species
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DDT and mosquitoes - Chemical change
Continual application of DDT pesticides on mosquito populations has lead to an increase in DDT resistant mosquitoes. The mosquitoes that have a natural resistance survive while others die and then these mosquitoes reproduce. Eventually most of the population in that area is resistant. |
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Describe thehistorical development of theories of evolution and assess social and political influences on these developments.
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19th century
- There was available evidence for evolution but not mechanism to explain how it occurred. - Darwin and Wallace independently arrived at natural selection to account for it - The19th century was a time of great industrial and political change. - The invention of machinery caused people to flock to the cities creating newproblems for well-established beliefs and people looked to science and newtechnology for solutions. - The social changes caused by cities’ changing the‘classes’ in society and the political changes, e.g. French Revolution,American Civil War and England expanding into an Empire provided an atmospherewhere people were prepared to investigate the scientific basis of allphenomena. |
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Describe Gregor Mendel's experiments
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- Established pure-breeding lines in pea plants for two years
- He then cross-bred to study to study inheritance of their characteristics/traits |
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What 7 characteristics/traits of the pea plants did Mendel study?
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o Flower colour, purple ofwhite
o Flower position, axial orterminal o Seed colour, yellow or green o Seed shape, round orwrinkled o Pod shape, inflated orconstricted o Pod colour, green or yellow o Stem height, tall or short |
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What were the results of Mendel's experiments?
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The initial offspring resembled one parent, but in later generations, the other parent's traits would arise
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What did Mendel's results show?
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- At that time, it was believed that if parents withcontrasting characteristics were crossed, the offspring would display a‘blending’ of characteristics.
His experiment showed this to be untrue. |
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Name and outline Mendel's laws?
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Law of dominance and segregation
- Traits of an organism are determined by a pair of factors - They may be the same (pure-breeding) or different (hybrid) - The trait that is expressed in the hybrid is dominant while the other is recessive -Traits are passed down according to set ratios - During gamete formation, the pair of factors segregate and each gamete receives only one factor for the trait Law of Independent assortment - when two or more characteristics are inherited, individual factors assort independently during gamete production, giving different traits an equal opportunity of occurring together. |
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What is a monohybrid?
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An individual that has contrasting factors for one characteristic
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Describe the aspects of the experimental techniques used by Mendelthat led to his success
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- Experiments were controlled
- Test only one variable at a time - His first-hand data was quantitative - leading to successful analysis of data |
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How did Mendel ensure reliability and validity?
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> changed one variable at a time + controlled all other variables > Used large sample size > Repeated experiments for different traits > Analysed results mathematically to identify patters and trends, then applied appropriate formulae to draw valid conclusions |
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How did Mendel ensure accuracy?
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- Reduced the possibility of experimental error
- Experiments were conducted in controlled environments ( agreenhouse) - Those crosses that relied on self-fertilisation (e.g. toestablish pure-breeding lines) were conducted by keeping the plants isolatedfrom any others to ensure no accidental cross-pollination - In plants that required cross-pollination, Mendel removed thestigma of some and the anthers of others and then manually transferred pollenfrom the anthers of one plant to the stigma of another |
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Why was Mendel's work not recognised until some time after it was published?
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Possible reasons are:
- He was not a high profile member of society - He presented his paper only to a few people at insignificant, local science meetings - Other scientists didn't understand the work and its importance - There was little knowledge of cells and no knowledge of genes |
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What are alleles?
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Alternativefactors of the same characteristics.
Different forms of genes |
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Define homozygous
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Factors/alleles that are the same e.g. TT, tt
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Define heterozygous
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Factors/alleles that are different e.g. Tt
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Difference between gene and allele
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A gene is a section of DNA coding for proteins that expressesitself as the phenotype of an organism.
Alleles are alternative forms of a gene. E.g. A gene for height and alleles for tall or short |
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Explainthe relationship between dominant and recessive alleles and phenotype
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Dominant alleles - the allele that is expressed in the phenotype of a heterozygote
Recessive - the allele that is not expressed in the phenotype of a heterozygote |
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What are human pedigrees currently used for?
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- Determine if particular family traits are geneticallyinherited
- Trace the occurrence of a genetic disorder, abnormality ordisease within a family over a number of generations - Deduce genotypes - Predict the likelihood of a family member inheriting a traitor disorder |
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Limitations of pedigrees
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-They are useful only when studying animals that do notproduce too many offspring
- For humans, their usefulness relies on accurate and reliablerecord keeping within families - It a family is small or has too few affected members,conclusions may be ambiguous - Sometimes the same genetic defect may be due to changes indifferent genes, so unrelated carriers of a similar defect may be inaccuratelyassessed as being at a high risk of having a ‘defective’ child |
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Describe an exampleof hybridization within a species and explain the purpose of this hybridization
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Example: Muel - cross between a horse and a donkey
Benefits: - Muel has desired characteristics from both parents but it is sterile - more patient, sure-footed, hardy and long-lived thanhorses, and they are consideredless obstinate, faster, and more intelligent than donkeys |
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What did Sutton and Boveri discover?
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- The role of chromosomes
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Describe Sutton's experiments and conclusions
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Studied meiosis in the cells of grasshoppers.
His studies showed that: - chromosomes occur in distinct pairs, visible during meiosis in grasshopper cells - During meiosis the chromosome number is halved - The chromosome pairs separate (Mendel's law of segregation) - Fertilisation restores full number of chromosomes in the zygote - Chromosomes arrange themselves independently across the middle of the cell Conclusion: - Chromosomes are the carriers of heredity |
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Describe Boveri's experiments and conclusions
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Worked with sea urchin eggs. He studied the behavior of the cell nucleus and chromosomes during meiosis and after fertilization.
He showed that: - The nucleus of the egg and sperm contribute the same number of chromosomes to the zygote - The offspring will show characteristics of both parents Conclusion: - A complete set ofchromosomes (i.e. chromosomes in pairs) is needed for normal development -The inheritance ‘factors’are found on chromosomes within the nucleus, i.e. chromosomes are the carriersof heredity |
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What are chromosomes made of?`
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- Chromosomes are long strands of hereditary informationcontaining genes made of:
o DNA: a long, thin thread-like macromolecule,which is the information-carrying part of the chromosome o Histone proteins: aroundwhich the DNA is coiled, to keep it neatly ‘packaged’. These proteins are madeof amino acids. |
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Name the complimentary base pairs of DNA
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Adenine and Thymine
Guanine and Cytosine |
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Describe the structure of DNA
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- Double helix (twisted ladder)
- Back bones of the structure (side of the ladder) are made of deoxyribose sugar and phosphate molecules - The rungs of the ladder are made of the complimentary nitrogenous bases |
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Where does genetic variation occur during meiosis?
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- Crossing over over of genetic information between homologous chromosome pairs
- Random segregation of chromosomes and independent assortment of genes - Random fertilization |
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Genetic variation in an individual arises as a result of:
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1. Sexual reproduction
- variabilityis introduced depending on which sex cells are successful in fertilization - The offspring will have genes from both parents 2. Gamete formation - During meiosis (random segregation, independent assortment, exchanging genetic information ) where the daughter cells are genetically different to parent cells |
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What is sex-linked inheritance?
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Genes that are carried on sex chromosomes that code for non-sexual body characteristics. (often on the X chromosome)
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Example of a sex-linked gene
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- Red green color blindness in humans
- Carried on the X chromosome only - Males only need one allele for color blindness on the X chromosome while females require too - Therefore color blindness is more common in males |
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What is co-dominant inheritance?
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When both alleles are dominant and so both are expressed as phenotypes (as a blend of both).
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Example of co-dominant genes
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In human blood groups there are 3 alleles:
A, B,O. A and B are both dominant while O is recessive. So there are 4 blood types: A, B, O, AB |
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Describe the work of Morgan that led to the understanding of sexlinkage
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- Thomas Morgan worked on the fruit fly Drosophila melanogaster (which normally have red eyes)
- He looked at crosses between red-eyed and white-eyed fliesand found that the results could not be accounted for by simple Mendeliancrosses - He discovered a mutant male with white eyes - He began crosses in a Mendelian sequence to show if the gene for white eyes would show typical Mendelian ratios |
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What crosses did Morgan do?
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- Cross 1: homozygous white male with a homozygousred female
- Cross 2: F1 hybrid offspring toobtain F2. He was expecting to get a Mendelian ratio of 3:1 but hedidn’t. Instead he got more than 80% red eyes and less than 20% white. At thispoint he thought that perhaps females couldn't have white eyes. - Cross 3: Crossed a white-eyed male with a hybrid red-female.This cross showed both males and females could have white eyes. |
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What did Morgan conclude from his work?
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He hypothesised that the white eye trait is ‘sex linked’ - carried on by the Xchromosome. He performed subsequent crosses that proved this to be true.
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How can the environment affect the expression of a gene in an individual?
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Some variations arise from genes, from the environment or both.
The effect of a gene can be masked or enhanced by variation in the environment. |
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Give an example of how the environment affects the expression of a gene
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Hydrangeas are plants that have different flower colors (pink or blue) depending on the pH of the soil.
Basic soils - Pink The pH affects the availability of ions in the soil and this causes the color to change. |
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Briefly outline the method of a first-hand investigation that demonstrates the effect of the environment on a phenotype
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- Place some genetic barley on moist cotton wool
- Grow one in the dark and one in the light (after they both germinated in the dark) - After a few days, compare their growth Dark: Tall, thin, yello Light: Short, wide, green |
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Describe the process of DNA replication
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1. The double helix is unwound by enzyme Helicase
2. The DNA unzips, forming two single strands 3. Nucleotides are added to the single strands, resulting in 2 identical strands of DNA (this is assisted by DNA polymerase) 4. Base paring is checked by another DNA polymerase to edit any incorrect additions and avoid mutation |
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Why is DNA replication important?
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It is important to pass on genetic information from generation to generation.
During sexual reproduction, the genetic code is copied and half the genetic information is passed into each sex cell. When fertilization occurs, the offspring has half the genetic code from the mother and half from the father. |
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Does DNA ever leave the nucleus?
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No
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How does RNA differ from DNA?
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RNA
- Usually single stranded - The sugar in the molecule is ribose sugar (not deoxyribose sugar) - It has nitrogenous base Uracil (U) instead of Thymine (T) |
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What are the 3 types of RNA?
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mRNA (messenger RNA) : Found in the nucleus and the cytoplasm. It is an intermediate molecule - carrying info from DNA in the nucleus to ribosomes in the cytoplasm
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Describe the process of protein synthesis
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1. RNA polymerase (enzyme) unzips DNA
2. Transcription of the gene occurs - RNA nucleotides pair up with single DNA strands forming single stranded mRNA 3. The mRNA moves out of the nucleus into the cytoplasm, where it encounters ribosomes 4. Translation - ribosomes move along the mRNA and attached the tRNA to the matching base pairs 5. The amino acids are linked together by another enzyme to form a polypeptide chain. The amino acids are spliced off the tRNA 6. The tRNAs move away from the mRNA to be reused, while the amino acid chain continues to grow. 7. The polypeptide chain may be joined with one more other polypeptides. They are further processed into proteins. 8. The mRNA is broken down into its individual nucleotides which can be reused. |
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Relationship between polypeptides and proteins
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A polypeptide is a chain of amino acids held together bypeptide bonds.
Proteins are large, complex macromolecules made up of onemore long chains called polypeptides |
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How do changes in DNA sequences result in changes in cell activity?
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If there is a change in the DNA code (e.g. mutation), this will eventually lead to different amino acids being produced.
This will lead to changed instructions which means a different polypeptide is produced or no polypeptides produced. Proteins control the metabolic activity of the cell |
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Briefly describe Beedle and Tatum's experiment.
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- Used bread mould to investigate nutritional mutations.
- They used X-rays to produce mould that was unable to synthesize a particular amino acid - The mould was unable to grow unless the amino acid was added to it - They showed that genes controlled biochemical processes |
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What did Beedle and Tatum hypothesise?
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- Their hypothesis was that for each gene there was on enzyme or protein
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What was Beedle and Tatum's hypothesis later changed to and why?
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The enzymes they studied consisted of one polypeptidehowever there are many enzymes that consist of chains of polypeptides.
Therefore the hypothesis was later changed to the ‘one gene –one polypeptide” hypothesis This shows that more than one gene may be responsible forproducing a protein |
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For mutations to persist and be passed on to future generations, where must the mutation occur?
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In the sex cells of the organism
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Describe some evidence for the mutagenic nature of radiation
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- Many scientists in the early 1900's worked with radiation unprotected (unaware of the effects) and so developed various illnesses.
- Between 1925 and 1940, experimental research providedevidence of the mutagenic nature of radiation - Hans Muller received the Nobel Prize in 1927 for showing thatgenes had the ability to mutate when exposed to X-rays - The atomic bombs dropped on Hiroshima and Nagasaki alsoincreased the evidence for mutations caused by radiation à there was a tenfoldincrease in cancer deaths |
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Explain Darwin's gradual evolution
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Small changes in each generation that accumulateover time so that the finalappearance is quite different fromthe original form
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Explain Punctuated equilibrium
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- Long periods where there is little change in organisms, followed bya shorter period where there are rapid changes
- Evolution is a sudden process rather than a gradual change |
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What is the evidence for punctuated equilibrium
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The evidence for this comes from the fossil record where massextinction of organisms followed by the appearance of new species
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What are the benefits of the discovery of the DNA structure?
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- Increased our understanding of heredity, variation and evolution by allowing scientists to describe the mechanism of inheritance in molecular terms
- Enhanced our understanding of hereditary disease and how the biochemical processes that occur in cells are related to macroscopic changes in the organism - Major impact on the development of new technologies e.g. recombinant DNA technology, DNA hybridization studies, genetic engineering, genetic screening for disease |
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What is artificial insemination? |
The injection of sperm-containing semen into a female's reproductive tract |
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What is artificial pollination? |
Transfers pollen from anthers of one plant to the stigma of another |
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What is cloning? |
Producing genetically identical organisms through non-sexual means |
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How do cloning, artificial insemination and cloning |
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