blueprint part 2

7/29/2019 Blueprint Part 2

1/11

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.


2/11

Biology HSC

Blueprint of Life

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


3/11

Biology HSC

Blueprint of Life

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.


4/11

Biology HSC

Blueprint of Life

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)


5/11

Biology HSC

Blueprint of Life

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


6/11

Biology HSC

Blueprint of Life

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.


7/11

Biology HSC

Blueprint of Life

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.


8/11

Biology HSC

Blueprint of Life

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.


9/11

Biology HSC

Blueprint of Life

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.


10/11

Biology HSC

Blueprint of Life

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


11/11

Biology HSC

Blueprint of Life

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.

blueprint part 2

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