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Biology HSC
Blueprint of Life
Outline the roles of Sutton and Boveri in identifying the importance of chromosomes
Boveri
Experimented on sea urchins and showed that a complete set of chromosomes is needed for normal development ofan organism. Unusual chromosome combinations led to abnormalities.
Chromosomes were not identical and a definite set is required for normal development - individualchromosomes must possess different qualities
Provided evidence for halving of chromosome numbers during meiosis Showed that chromosomes were transferred during meiosisChromosomes are the means of inheritance
He showed a connection between heredity and chromosomes.
Sutton
Observing meiosis in grasshoppers, Sutton proposed that genes (Mendels factors) are carried on chromosomes and
the chromosomes behave and separate like Mendels factors. His experiment on grasshoppers revealed that:
Chromosomes occur in distinct pairs of same size and shape, visible during meiosis one from the father(paternal) and one from the mother (maternal). Today these are called homologous chromosomes.
During meiosis, the chromosome number of a cell is halved -> Just like segregation of Mendels factors! Fertilization restores the full number of chromosomes Since there are far more hereditary factors/genes then there are chromosomes, each chromosome must
carry many heredity units.
Sutton-Boveri were responsible for the chromosomal theory of inheritance Chromosomes carry many units of
inheritance (genes) and occur in distinct pairs.
Describe the chemical nature of chromosomes and genes
Genes are short lengths of DNA and soare made up of a sequence of
nucleotides Nitrogen bases, sugars
and phosphates.
Chromosomes are made up of DNA,coiled around proteins called histones.
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Identify that DNA is a double-stranded molecule twisted into a helix
Each nucleotide consists of a nitrogen base, attached to a sugar andphosphate.
Bases are attached to sugar-phosphate backbone as well as acomplementary strand
A is paired to T and G is paired to C
Explain the relationship between the structure and behaviour of chromosomes during meiosis and the
inheritance of genes
During meiosis, each chromosome makes a complete copy of itself. The duplicate chromosomes(chromatids) are attached to the originals by centromere.
Homologous chromosome pairs line up in at the equator of the cell. Crossing over occurs, where sections ofchromosomes are traded within the homologous pair
o This means that linked genes which are located on the same chromosome from the same parent,can be separated by crossing over.
In the first division of meiosis, homologous chromosome pairs randomly separate into two new cells, so thateach of the two new cells has half of the genetic information of the original, but a duplicate copy of eachchromosome.
In the second division of meiosis, duplicated chromosomes separate to single strands, resulting in fourdaughter sex cells that are haploid
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Explain the role of gamete formation and sexual reproduction in variability of offspring
Gamete formation (meiosis) Allows recombination of genetic material through crossing over and random
segregation.
Crossing over Homologous chromosomes exchange genes so the resulting combinations of alleles on chromatids
differ from original parent chromosomes. This can change linked genes and allows for greater variability in the
combination of genes in gametes.
Random segregation and independent assortment Each homologous chromosome could enter any gamete so each
gamete will have a combination of maternal and paternal chromosomes. It increases variability as it allows for more
combinations of genes in gametes.
Fertilisation and variability Each gamete contains different combinations of alleles for each gene. Since this occurs
in both parents, when gametes meet there is a high level of variability. There are also many gametes from each
parents so there are many possible combinations when they fuse.
Describe the inheritance of sex linked genes, and alleles that exhibit co-dominance and explain why these do not
produce simple Mendelian ratios
Explain the relationship between homo & heterozygous genotypes & the resulting phenotypes in codominance
Describe the work of Morgan that led to the understanding of sex linkage
Morgan studied the fruit fly as:
Had easily observable characteristics carried on only four pairs of chromosomes Produce hundreds of offspring in a single mating and produce a new generation every 10-12 days
The normal eye colour is red, however Morgan found a white eyed male, probably a mutant. He crossed this white
eyed male with a red eyed female and all the F1 had red eyes. He mated these and the F2 generation produced a 3:1
ratio of red to white. HOWEVER, only the males had white eyes.
Conclusion: White eyes is recessive and sex-linked, located on the X chromosome.
The F1 offspring: Red female XRX
rcrossed with Red male X
RY cannot produce a female white fly (X
rX
r), only a male
white fly (XrY)
Outline ways in which the environment may affect the expression of a gene in an individual
Genotype + environment = phenotype. An organisms genetic potential to express a characteristic may be limited by
the environment.
Humans: two people with the same genes for growth may not be the same size and height as malnutrition or poor
health can cause stunting.
Siamese catsare born white. They have a gene that codes for a protein enzyme which catalyses pigment production.
This gene is heat sensitive and will only act in cool conditions, hence why the ears and feet are usually coloured.
Hydrangea plantsproduce flowers of different colours, depending on acidity of soil. Acid soils cause bright blue
pigmentation while alkaline soil causes pale pink colour.
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Describe the process of DNA replication and explain its significance
The DNA double helix is unwound by helicase. The weak hydrogen bonds break and it becomes two strands. Each exposed strand acts as a template as a complementary copy is constructed. Adenine is paired to
Thymine and Guanine is paired to Cytosine. The complementary bases are picked up by DNA polymerase and
attached to their complementary base in each exposed strand.
Replication of one strand begins at the fork while the other begins at one end going towards the replicationfork.
The base pairing is checked by another polymerase enzyme which edits any incorrect additionsSignificance of DNA replication:
In Meiosis, identical copies of DNA can be made so genetic information can be passed onto offspring,ensuring continuity of a species
In Mitosis, genetic information is passed onto new cells and this process is essential for growth, repair andmaintenance of an organism.
Outline using a simple model the process by which DNA controls the production of polypeptides
1) In the nucleus, an enzyme called RNA polymerase unzips the DNA, breaking the hydrogen bonds.2) Transcription: One strand of DNA acts as a template and a strand of mRNA is created with complementary
bases to the DNA strand. T is replaced by U on the mRNA. This is controlled by the polymerase.
3) Translation: The mRNA moves to the cytoplasm. Here the ribosomes move along the mRNA and attach tRNAcarrying amino acids. The codons (groups of 3 bases) on the mRNA are attached to complementary anti-
codons on the tRNA.
4) The amino acids form a polypeptide chain based on the sequence of bases.Explain the relationship between proteins and polypeptides
Proteins are large and complex, made up of one or more polypeptide chains. One of more polypeptides can be
twisted together into a particular shape which results in the overall structure of a protein. Polypeptides are chains of
amino acids.
Analyse information from secondary sources to outline the evidence that led to Beadle and Tatums one gene
one protein hypothesis and to explain why this was altered to the one gene one polypeptide hypothesis
The experiments of Tatum and Beadle:
Worked with bread mould Neurospora and they grew it in a minimal agar one without the full blendneeded for growth.
The bread mould still grew so they concluded it must have genes that produce enzymes to manufacturemissing substances
They used radiation and x-rays to produce (after almost 300 attempts) a mutated strain of the mould. This grew in the complete agar medium but not the minimal They used different mediums with only one amino acid/vitamin removed to determine which enzyme was
lacking in the mutant strain. The gene that allowed production of vitamin B-6 no longer functioned
From this they concluded that one gene codes for one proteinLater changed to one gene one polypeptide as some proteins are made up of more than one polypeptide (e.g.
haemoglobin is made up of four polypeptide chains)
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Explain how mutations in DNA may lead to the generation of new alleles
Mutations can be:
Spontaneous mutations Arise randomly in natural processes such as DNA replication Induced mutations Arise as a result of a mutagen, an environmental agent that causes mutation
Gene mutations:
Point mutation one pair of bases (e.g. A-T) is replaced by another (e.g. C-G). This causes a single incorrectamino acid in a polypeptide chain. The protein will have abnormal function. An example is in the production
of haemoglobin, resulting in the disease sickle cell anaemia
Frame shift Bases are added or deleted from a strange of DNA, changing the whole sequence ofnucleotides. The wrong amino acids will be used in the polypeptide chain and the protein will not perform its
function. E.g muscular dystrophy causes muscles to be produced incorrectly and break down
Chromosomal mutations
One extra or less chromosome then normal can be caused by deletion, duplication or attachment to eachother. This prevents the gene from producing a functional protein throughout the whole body. An example is
down syndrome where individuals have three copies of chromosome 21.
Mutations can be harmful, neutral of beneficial. Natural selection will keep beneficial traits in a species and remove
harmful ones as these characteristics alter the chance of an organisms survival and ability to reproduce.
Process information to construct a flow chart that shows that changes in DNA sequences can result in changes in
cell activity
Sickle Cell Anaemia
Point mutation occurs in gene for haemoglobin production one base
is replaced by another
Single incorrect amino acid is put into the polypeptide chain
Protein (haemoglobin) formed causes red blood cells to form a
sickle shape
Blood vessels may become blocked due to abnormal shape
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Discuss evidence for the mutagenic nature of radiation
Mutagen: A natural or human made agent which can alter the structure or sequence of DNA (mutations).
Most of the scientists who first worked with radiation died of cancer. E.g. Marie Curie died of leukaemia. In 1926, Hermann Muller performed experiments where he exposed reproductive cells of fruit flies to
radiation. He showed that genes could mutate when exposed to x-rays. The larger the dose was, the higher
the rate of mutation. He was awarded a Nobel Prize.
Beadle and Tatums work with bread mould used radiation to cause changes in genes The Chernobyl nuclear accident caused high levels of infertility and genetic mutations Atomic bombs dropped on Hiroshima and Nagasaki released radiation. A tenfold increaser in cancer deaths
soon followed.
Radiation used as a cancer treatment provides evidence for the mutagenic nature. Because cancer cells areconstantly dividing and undergoing DNA replication, they are susceptible to the effect of radiation on DNA.
Explain how an understanding of the source of variation in organisms has provided support for Darwins
theory of evolution by natural selection
Sources of variation:
Mutation Random segregation and independent assortment of chromosomes Crossing over in homologous chromosomes Random fusion of games during fertilization
This genetic variation causes changed in the phenotype of an organism. A changed phenotype may be beneficial,
allowing an organism to better survive and reproduce, or detrimental which will limit survivial.
Variation is fundamental to Darwins theory of natural selection so understanding the source of variation provides
support.
Process information from secondary sources to describe and analyse the relative importance of the work of
scientists in determining the structure of DNA and the impact of the quality of collaboration and communication
on their scientific research
Franklin:
Probably the most important. She built more advanced x-ray diffraction technology and produced thephotograph 51 x-ray image of DNA that led Watson and Crick to finally build an accurate model.
She guessed the phosphate backbone was on the outer side and would have eventually figured out thestructure if her work was not shared prematurely.
A strained relationship with Wilkins arose from a miscommunication about who was in charge. Rosalind wasassertive and articulate while Wilkins was shy and deliberate.
If she had of collaborated with Watson and Crick they would have figured out the problem far quicker.Wilkins:
Produced an early, fuzzy image of DNA. Shared Franklins work with Watson and Crick, diminishing the value of her findings.
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Watson and Crick
Examined the work of Franklin, Chargraffs research on amount of bases and Paulings discovery of thehelical shape of proteins.
Published an accurate double helix model of DNA. They suggested pairing of bases that made a possiblecopying mechanism for genetic material.
Had a close working relationship and were good friends, allowing them to persist even after their first modelfailed.
The positives that can be gained from collaboration include:
Effective use of individual talents and skills - Due to the complexity of research, combining skills ofresearchers or knowledge can lead to quicker solutions to problems.
Knowledge is shared more easily and quickly as it normally takes a considerable amount of time to appear inwriting for researchers working alone.
May inspire or stimulate new ideas - Views or findings of others can stimulate new ideas and ways ofthinking and approaching problems.
Identify how the following current reproductive techniques may alter the genetic composition of a population
Note: Genetic engineering is only considered a reproductive technology if the new gene assists reproduction
Artificial Insemination
Artificial insemination is the injection of male semen in the cervix of a female without sexual intercourse. Sperm is
collected from a male with desirable characteristics then is used to inseminate many females. Is often transported
long distances. Desirable characteristics include: better milk production, disease resistance, more muscle.
While it allows for introduction of new alleles, overuse of sperm from one bull can reduce genetic diversity,with the same phenotype being more common in offspring.
Characteristics of male can be quickly brought in so the genetic composition of the population is rapidlyaltered.
Artificial Pollination
This involves taking the pollen from one plants stamen that has desired features and placing it on the stigma of
another flower. Desirable characteristics include: Disease resistance, larger fruit and higher yield.
Allows the breeder to alter the genetic composition of a population to include desired characteristics Overuse of one strain in a large monoculture will reduce genetic variability in the population. If a selective
pressure appears such as a disease, the whole population can be wiped out. E.g. in the Irish potato famine.
Cloning
Cloning produces organisms genetically identical to the parent
Reduces the genetic variability of a population. If a selective pressure such as a disease is introduced, thewhole population of cloned organisms could be wiped out.
Alternatively, can be used to maintain genetic diversity if a plant or animal is endangered.
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Process information from secondary sources to describe a methodology used in cloning
Cloning can be:
Reproductive cloning Involves creating a genetically identical, whole organism using a cell from anothermature organism. This is asexual reproduction with only one parent.
Therapeutic cloning Using cells from an individual to produce a cloned early embryo which is then used forembryonic stem cells to replace degenerating tissue and repair damage. Not a new whole organism but a
source of cells.
Gene cloning At a cellular level and involves producing identical copies of a gene.The process by which animals are cloned is called Somatic Cell Nuclear Transfer (SCNT)
Nucleus from a body cell (somatic cell) of an organism to be cloned is taken and starved of nutrients so itdoes not divide.
An egg cell is taken from another animal of the same species and the nucleus is removed. The somatic cell is inserted into the egg cell and an electrical stimulus is used to fuse them and stimulate cell
division.
At a certain stage in cell division, the embryo is implanted into a female surrogate mother.
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Outline the processes used to produce transgenic species and include examples of this process and reasons for
its use
Biotechnology is any technique that uses organisms and biological processes to make products. Genetic engineering: The use of technology to manipulate genetic material of an organism and alter
characteristics
Transgenic species: A species with genes from another species in its genetic code. A GMO is not a transgenicspecies unless it is able to pass on the genetic modification to offspring.
The process used to produce transgenic species is as followed:
A desired gene and the chromosome it is must are identified The gene is cut from the DNA by using restriction enzymes, known as restriction endonucleases. They form
the sticky ends (the cut ends) of a gene.
Plasmid DNA is isolated from a bacterium. The gene is inserted into the plasmid DNA to make recombinant plasmid DNA. The plasmid is put into a bacterial cell. The cells divide, cloning the gene. The copies of the gene are cut out of bacteria plasmids and inserted/injected into an egg cell of another
species. After fertilization, the gene becomes part of the newly formed organisms DNA.
Inserting a gene (gene delivery) can be achieved through:
Micro-injection of DNA directly into the nucleus of a single cell Biolistics: DNA on microscopic particles is fired from a gene gun into target cells e.g. tiny gold particles used
to coat the gene
Electroporation: Increasing the permeability of the cell membrane by applying an electric current. Transduction by a viral vector: injected directly into the bloodstream or taken by aerosol
Incorporation is assessed by:
Using a gene for a fluorescent protein to determine whether the gene has been incorporated and acts as amarker.
Example The process used to produce BT cotton
Cotton seedlings were cut into pieces and grown in growth mediums until they developed into cottonembryos
The BT gene was extracted from the bacterium using restriction enzymes The BT gene was transferred into the cotton plant embryo. This was done by dipping plant embryos into a
solution that had the gene recombined with the genome ofagrobacterium. These bacteria acted as a
vector/carrier, injecting the BT genes into the cotton cells.
Embryos grown in tissue culture, placed on a solid medium and when they germinated they were potted andgrown in a greenhouse.
BT cotton is used to reduce damage to crops from pests. It allows farmers to rely less on chemical pesticides. Thisbenefits the environment by reducing spray drift, it causes less damage to beneficial insects that predate pests and it
means less chemical pesticide resistance occurs. It also reduces the labour and cost of continually spraying.
More general reasons for transgenic use are shown inforethical issues below.
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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
Example BT cotton. A gene from the bacteria Bacillus thuringiensis has been inserted into cotton. This gene codes
for a protein which is toxic to the heliothis caterpillar.
Example AquAdvantage salmon. A growth hormone gene from Chinook salmon has been inserted into the Atlantic
salmon, allowing them to grow at a much faster rate.
Ethical Issues:
For Against
Can ease world hunger Genetic engineering forbetter nutrition, higher yield and crops that can be
grown in marginal soils can reduce food crisis.
If we are able to produce products that benefit thosein need, it is unethical not to.
Crops could be created to be more drought, salt andpest tolerant, allowing better income. Financial
income is essential to keep farmers who produce the
food in business.
Reduced use of pesticides due to naturalmechanisms such as BT can reduce the impact on
the environment and beneficial insects and reduce
pest resistance to chemical insecticides.
Plants may be able to more efficiently use resourcesthat are difficult to renew or completely non-renewable.
Use of GM crops may become widespread leading todecreased genetic diversity so poor protection
against selective pressures such as disease
Animals may be created to suit production needs ofthe farmer and not needs of the environment, so
may reduce survival and reproduction rates.
Is it wrong to alter natural processes it may havean effect on other organisms.
If a gene from a pig is inserted into a vegetable, thiscan create religious barriers.
If a human gene is put into an animal, this could beseen as cannibalistic
Inserting genes can cause allergic reactions e.g. apeanut bean put into soy beans
Long term health risks may be present and notdiscovered until later in life
Patenting of genes means single companies cancharge large amounts for seed. They may also
produce seed that will not reproduce, meaning the
farmer must buy it each year.
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
Bio-diversity: The variety of all living organisms including plants, animals, micro-organisms, their genes and their
ecosystems.
Genetic diversity: The genetic variation within a species.
AquAdvantage salmon: A gene that regulates growth hormones was taken from the DNA of Chinook salmon
inserted into the DNA of an embryo in an Atlantic salmon egg. They are grown in holding facilities as not to release
the gene into the ecosystem. The gene assists reproduction so this is considered reproductive technology.
At first, genetic diversity will be increased as new alleles are added to the population. Better growth makes males more attractive to females so they will mate more The genetic diversity of the population will decrease as natural selection will allow these salmon to better
survive and reproduce
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BT cotton: When the BT gene is added to the cotton, it must be propagated by cloning (such as a tissue culture or
grafting) or artificial pollination.
At first, genetic diversity will be increased as new alleles are added to the population Farmers will use only the BT cotton crops as they produce better yield so traditional cotton varieties will stop
being used and genetic diversity will be decreased.
As the crops will all be genetically very similar or identical if cloned, a selective pressure may wipe at theentire population.