Genetics the Code Broken

Biology HSCGenetics: The Code Broken?

Describe the processes involved in the transfer of information from DNA through RNA to the production of a sequence of amino acids in a polypeptide

Transcription: process by which information on DNA is copied onto an RNA molecule i. DNA strand in nucleus unwinds in area of required gene, controlled by RNA polymerase (helicase action)

which breaks the weak hydrogen bondsii. RNA polymerase moves along the strand linking complementary RNA nucleotides to form the pre-mRNA

strandiii. After the whole gene is copied, introns (non-coding regions) are spliced from the pre-mRNA and exons

(coding regions) are joined together to form mRNAiv. A chemical nucleotide cap is added to each end. The chemical cap assists in binding the mRNA to ribosomes

and prevent breakdown by hydrolytic enzymes.v. mRNA moves from nucleus into cytoplasm

Translation: process by which information on RNA molecule is used to make a new proteini. mRNA attaches to ribosome

ii. The codons (groups of 3 bases) on the mRNA are attached to complementary anti-codons on the tRNA. The tRNA are carrying amino acids specific to that codon and when they attach, the amino acid is released onto the polypeptide chain. Amino acids are joined by peptide bonds.

iii. When a ‘stop’ codon is reached the polypeptide chain is released into the cytoplasmiv. Further processing and folding is necessary before final protein is formed, as polypeptide chain is only

primary structure

Choose equipment or resources to perform a first-hand investigation to construct a model of DNA

Equipment and resources:

Different coloured pieces of paper used to represent each base and the sugar/phosphate backbone Scissors to cut out pieces Different coloured pens to draw on sugar and phosphate molecules Glue to piece together the model

Limitations

The size was not completely accurate with relative pieces not sized correctly Only a small section of DNA could be modelled The structure of DNA around histone/on chromosomes could not be shown Over simplified a more complex structure

Process information from secondary data to outline the current understanding of gene expression

A quick note: There are two other types of DNA – Mitochondrial and Chloroplast DNA, responsible for enzymes that assist in cellular respiration/photosynthesis respectively.

A gene is fully expressed when its polypeptide is synthesised, converted to a protein and the protein is fully functional.


DNA unpacking

DNA is wound around proteins called histones, this helps to store large amounts of DNA Genes switched off may be packed more tightly or highly condensed

Regulation of unpacking

– Additions of methyl groups to DNA stops unpacking and gene expression– Addition of acetyle group binds to the histone, causing it to bind less tightly and unwind and transcribe

more easily

DNA transcription

Control point for gene expression DNA is transcribed by RNA polymerase Each gene has its own promoter, which may be activated by the presence or absence of a chemical. The

promoter activates RNA polymerase for that gene There is a large amount of DNA not coded into protein. Non-coding areas are INTRONS. Coding areas are

EXTRONS. Introns are cut out before the mRNA leaves the nucleus and extrons are spliced together. The ends of transcribed mRNA are capped to prevent breakdown by hydrolytic enzymes and

Regulation of transcription

– Segments can be treated as introns or extrons in different cases, producing different mRNA when extrons are spliced together.

– Caps can be removed from ends of mRNA which greatly reduces its life and stops protein synthesis when it is broken down

– The movement of mRNA out of the nucleus can be prevented to stop gene expression

DNA translation

– Specific proteins can bind to mRNA so that it cannot attach to mRNA. This will stop translation and gene expression.

Protein processing and degradation

– Folding, cleaving or adding non-protein sections such as carbohydrates or lipids will prevent the fully functioning protein being produced

– Since proteins must be transported to the site of action, they can be transported elsewhere and broken down

Give examples of characteristics determined by multiple alleles in an organism other than humans

While each organism will only have 2 alleles for a characteristic, a population may consist of many different alleles. For example hair colour can be black, brown, agouti, grey etc.

Some rabbits have 4 alleles for hair colour. One allele is always dominant, one is always recessive, however the other two can be either depending on what alleles are present.

Full colour > Chinchilla > Himalayan > Albino


Hair colour in rabbits C = full colour cc = Chinchilla ch = Himalayan c = albino

White spotting in dogs s = white spots absent si = Irish spotting sp = piebald spotting S = extreme spotting

Compare the inheritance of the ABO and Rhesus blood groups

Rhesus Factor:

Rhesus factors are an example of Mendelian dominant inheritance There are 2 alleles: D, d D is dominant over d There are 2 possible phenotypes: Rh+, Rh-

Comparison of Inheritance Patterns:

ABO blood group: 3 alleles, 6 genotypes, 4 phenotypes Rhesus factor: 2 alleles, 3 genotypes, 2 phenotypes

Example Punnet Squares: 75% B+, 25% O+

Solve problems to predict the inheritance patterns of ABO blood groups and the Rhesus factor

Define what is meant by polygenic inheritance and describe one example of polygenic inheritance in humans or another organism.

Polygenic inheritance refers to a trait that involves more than one pair of alleles, e.g. human height is not the result of a single gene, but multiple. Polygenic inheritance produces large variations in phenotype and genotype.

Where n is the number of genes for the trait the number of possible phenotypes = 2n + 1

Skin colour

Controlled by 3 genes Aa, Bb and Cc. An upper case letter adds darkness to the skin, causing more production of melanin and pigmentation. A lower case letter does not contribute to the trait The number of capital letters therefore corresponds to the darkness of a trait

Genotype PhenotypeDD Rh+Dd Rh+dd Rh-

IB D i D

IB d IB IB Dd IB i Dd

i d IB i Dd i i Dd


Possibilities AABBCC – Very dark AABBCc AABBcc AABbcc AAbbcc Aabbcc aabbcc – very light or albino

The Reality of Skin Colour: There is further variation due to environmental factors such as exposure to UV radiation. These variations smooth out the histogram into a smooth curve. Also some skin colours are more common as there are more possible genotypes for that phenotype, e.g. AABBCC can only be made 1 way, AaBbCc can be made 17 ways.

Outline the use of highly variable genes for DNA fingerprinting of forensic samples, for paternity testing and for determining the pedigree of animals

Highly variable genes: DNA in some regions of the human chromosome consists of specific non-coding sequences that are repeated

in tandem. The number of repeats of a given sequence varies from person to person. For example: a person may have 4 repeats (CATCATCATCAT) and 6 repeats (CATCATCATCATCATCAT) on his

homologous pair of number-7 chromosomes, while another person could have more or less.

DNA fingerprinting of forensic sample: Forensic samples such as hairs from a crime scene are taken. DNA is extracted from a sample with chemicals Identical patterns of fragment sizes (i.e. matching bands when the fragments are separated by length)

suggest identical sources of DNA. As more identical DNA sequences or matching bands are found, the probability of identification increases.

Paternity Testing: Half of a child’s DNA comes from its mother and the other half from its father. When comparing profiles of

hyper variable regions of DNA, half of a child’s bands come from its mother and the other half from its father. Each band in a child must come from one or the other of its biological parents.

Therefore, if the child has a lot of fragments that are neither present in the mother nor the father, it is highly likely that one of them is not the child’s biological parent.


Determining the pedigree of animals: In breeding pedigreed animals, knowledge of an animal’s sire (father) and dam (mother) must be certain. Mistakes in assigning parents can occur due to semen/embryo mix-ups during artificial insemination,

mistakes in record keeping, or when accidental matings occur. The use of DNA profiling to definitively identify an animal’s biological parents allows breeders to be certain

that their animals have the ancestry which they claim, and also prevents breeders from faking pedigrees.

Use the terms ‘diploid’ and ‘haploid’ to describe somatic and genetic cells

Body/somatic cells have the diploid number (2n) of chromosomes and so are called diploid cells. This is the full set of chromosomes. In humans there are 23 homologous pairs making up 46 chromosomes in a diploid cell.

Genetic cells (germline cells/gametes such as sperm and ovum) contain half the number of chromosomes (n) and so are haploid cells. They have one chromosome from each homologous pair. When two haploid cells join (i.e. sperm meets ova at fertilization), a diploid cell is made. Human haploid number is 23 chromosomes.

Describe outcomes of dihybrid crosses involving simple dominance using Mendel’s explanations

Tall stem (T) is dominant over short stem (t), and round seed (R) is dominant over wrinkled seed (r)

Two plants are crossed, each heterozygous for both stem height and seed shape

Parents: TtRr x TtRr Possible gametes: TR, Tr, tR, tr and TR, Tr, tR, tr

Phenotypic ratios: 9 tall-round : 3 tall-wrinkled : 3 short-round : 1 short-wrinkled

Predict the difference in inheritance patterns if two genes are linked

Genes for different characteristics on the same chromosome are called linked genes and these will not assort independently at meiosis unless crossing over occurs.

E.g. For two genes on a pair of chromosomes, if one contained AB and it’ homologue had ab, Mendel’s model of inheritance would predict that possible gametes could include: AB, Ab, aB, abSince these genes are linked they will remain together (unless crossing over occurs) and so gametes could include:AB, abIf 2 linked genes are further apart on a chromosome, the chance that they will be separated by crossing over is greater. The relative distance between two loci (gene positions) corresponds to the probability of crossing over

If alleles A-B are 10 cM apart and a-b are cM units apart on the homologous chromosome, there is a 10% chance of recombinant gametes. The gametes will be 45% AB, 45% ab, 5% Ab, and 5% aB

Note: a ‘map unit’ or a centrimorgan (cM) corresponds to about 1 million bases. A map unit/centrimorgan corresponds to the occurrence of 1% recombinant gametes from the relevant test cross.

gametes TR Tr tR tr

TR TTRR TTRr TtRR TtRr

Tr TTRr TTrr TtRr Ttrr

tR TtRR TtRr ttRR ttRr

tr TtRr Ttrr ttRr ttrr


perform a firsthand investigation to model linkage

Explain how crossbreeding experiments can identify the relative position of linked genes

Background- In 1913 Alfred Sturtevant constructed the first genetic map of a chromosome for specific genes in the fruit

fly- He worked out that the genes were in a linear order along the chromosome and you could determine the

order of genes along the chromosome by studying the frequency of crossing over

Recombination: any process that gives rise to offspring that have combinations of genes different from those of either parent, such as crossing over and independent assortment of chromosomes during gamete formation

In these tests, a double heterozygote is always crossed with a double homozygous recessive individual e.g. AaBb x aabb.

First remember: The further linked genes are apart, the more likely crossing over is to occur.

The idea is to find what % of offspring are RECOMBINANT (different to parents genotype) because this occurs due to crossing over. Then obviously this % = the distance genes are apart.

The offspring produced will be: AaBb, Aabb, aaBb, aabbSo one offspring same as father, one same as mother, and two possible different/recombinant ones.

THE % OF RECOMBINANT OFFSPRING = THE cM GENES ARE APART

Here's an example, if 5% of the offspring were Aabb and 5% were aaBb that means there's 10% total recombinant offspring yes. So 10% of these = linked genes are 10 centrimorgans apart.

Discuss the role of chromosome mapping in identifying relationships between species

Chromosome mapping is simply a linear sequence of genes on a chromosome. It allows us to identify the arrangement of linked genes and their relative distance from each other.

Similarities in these arrangements between organisms indicate a relationship between the species. More similarities indicates a closer relationship, i.e. the species diverged more recently.

Diploid chromosome numbers can indicate relationships, e.g. great apes have 48 and humans have 46 While alleles are crossed over, gene loci remain the same Rats and mice have many groups of linked genes similar. 50 genes on rat’s number 3 chromosome also

appear on a mouses number 2 chromosome.Disadvantages:

Does not show actual distances, just order of genes and relative distances. May not fully represent a chromosome. Subject to error when recombination/crossing over rates vary between species

45% AB 5% Ab 5% aB 45% ab100% ab 45%

AaBb5% Aabb 5% aaBb 45% aabb


Discuss (and explain) the benefits and limitations of the Human Genome Project

The Human Genome Project (HGP) was started in 1989 and finished in 2003. Its goals included: Identifying positions on chromosomes of all 25-30,000 genes in human DNA Determine the base/nucleotide sequences of each gene

Benefits:

Greater scientific understanding of gene expression, mutation and interaction, e.g. gene cascades Greater understanding of genetic control in developing human, i.e. growth and development Better understanding and unravelling of non-coding intron regions of DNA Improvements in molecular medicine

o Diagnosis of inherited disorders due to a single gene, e.g. cystic fibrosis o Better drug design tailored to cause of the disease, e.g. gene therapy for cystic fibrosiso Ability to assess heritable mutations, e.g. if both parents carry recessive alleles for an inherited

recessive disease More accurate assessment of the risk of mutagens such as radiation and chemicals Further evidence and understanding of evolution by studying mutations, gene sequences, chromosomes and

linked genes Genes can be identified for use -> Cloned for disease treatment e.g. insulin, or used for genetic engineering Providing grants for innovating research and licensing technologies has accelerated the biotechnology

industry, aiding medical and biotech applications Use in DNA forensics to more easily identify and match DNA bands Benefits in agriculture – using the technology to map genome of agricultural animals and plants could lead to

development of more nutritious, higher yielding, disease, pest and climate resistant organisms.

Limitations:

Raw data of base sequences on their own are fairly meaningless and a great deal more research is needed before benefits can be seen, e.g. structure and function of actual proteins produces by genes

Does not explain the majority of human biochemistry and scientists still believe many parts such as brain function will never be fully understood

Raises many ethical questions:o How will humans use such knowledge and can and will it be patented – who has access and what

regulations will govern its useo Knowledge could be used to discriminate against some considered ‘genetically inferior’o Insurance and job access has been refused in the US due to known genetic problems, if all genetic

risk was known this could happen on a much larger scale, creating an inequitable system Much of the non-coding intron information is useless, only 3% of DNA codes for proteins Extremely large amounts of money were spent on the project and it has been suggested it was far more than

the value of the results

Process information from secondary sources to assess the reasons why the Human Genome Project could not be


achieved by studying linkage maps

Linkage maps would not be useful for the HGP as: They reveal relative positions of genes on a chromosome, while the project requires exact positions Do not sequence nucleotides or bases that make up genes Does not determine which particular chromosome a gene lies on Cross breeding experiments used in gene mapping would be unethical to perform on humans and take an

extremely long time Gene mapping is based on recognisable characteristics, while many genes have subtle functions not

recognisable Linkage maps only identify coding regions (exons) and not the non-coding introns

Outline the procedure to produce recombinant DNA

1) A gene is cut out of the chromosome using restriction enzymes. ‘Sticky ends’ are formed where cuts are made.

2) Circular DNA (plasmid) from a bacteria and cut using the same restriction enzyme3) The gene is mixed with the bacteria plasmid and DNA ligase is used as a ‘glue’ to allow the gene and

plasmid to recombine at matching sticky ends4) Plasmids are reinserted back into bacteria by adding calcium chloride to increase permeability of

bacteria membrane5) Bacteria reproduces and plasmids are cloned, cloning the recombinant genes6) The bacteria will also express the protein now introduced into its genome

explain how the use of recombinant DNA technology can identify the position of a gene on a chromosome

The position of a gene is found by creating a fluorescent probe that will attach to it.

1) The gene of interest must be sequence, i.e. the base sequence must be known

2) Heat is used to separate the two DNA strands into single strands

3) A fluorescent probe is created. This is a single strand of DNA that is made to be complementary to the bases of the gene and it can easily be identified

4) The single stand of the probe will recombine with the single strand of the gene

5) Looking under a microscope, the location of the gene can then be easily seen

describe current use of gene therapy for an identified disease

Gene therapy: Replacement of defective or faulty genes with healthy ones

Somatic gene therapy – replacing defective genes in somatic cells Germ line gene therapy – Replacing defective genes in gametes or embryo. Changes will be inherited

and last lifetime

Gene therapy can be:


In Vivo – introducing genes to tissues or organs without removing body cells. Must be delivered only to intended tissues

Ex vivo – Gene removed and treated in the lab to fix problems. More effective.

Cystic Fibrosis

Recessive condition caused by a mutation to the cystic fibrosis transmembrane conductance regulator gene (CFTR)

It results in the lack of production of a protein that is responsible for pumping ions across cell membrane. It means chloride ions cannot effectively move across. Cells absorb water to try and dilute the ions and the result is a buildup of thick, sticky mucus, mainly in the lungs.

Cystic fibrosis is very suitable for gene therapy as:o It is a single gene, so only one gene needs to be treatedo The main organ affected (lungs) is quite accessible for treatmento People with the condition have relatively normal lungs at birth so treatment can be started

early to reduce damage taking place

Somatic, in vivo gene therapy is used to repair the CFTR gene:

Gene therapy to replace defection CFTR genes with functional genes so a functional transmembrane conductance regulator protein is produced

o Most recently, this has involved using a nebulizer to inhale harmless/disarmed adeno-associated viruses that act as a vector to deliver fixed gene into lung cells.

o Previously, a drip through the nose and other direct methods were used and a doctor was needed.

Distinguish between mutations of chromosomes including

Rearrangements Deletion – where part of a chromosome breaks off and a gene is lost from the chromosome, e.g. Chit-

du-Chat syndrome where a deletion from Chromosome 5 occurs Duplication – where the same section of a chromosome is copied or occurs twice. May be copied onto

the homologous chromosome Inversion – order of genes is reversed. Occurs due to breaking and rejoining in opposite directions Translocation – part of the chromosome breaks off and attaches to another, e.g. breakages in 21 can

cause down syndrome

Changes in chromosome numberCan occur during meiosis if homologous chromosomes don’t separate. This is called non-disjunction and resultsin some gametes with extra or less chromosomes.

Trisomy – There is an extra copy of one chromosome, e.g. down syndrome is caused by trisomy-21 where there are 3 number 21 chromsomes.

Polyploidy – When meiosis fails completely in one parent and an offspring inherits a full extra set of chromosomes (3n). This is common in plants, but fatal to humans.

Genic Mutations


Base substitution – Occurs when one base is replaced by another. The polypeptide will have one wrong amino acid.

Frame Shift – Extra bases are added or deleted from a gene and will affect the whole base sequence, making a completely different and usually non-functional polypeptide.

Process and analyse information from secondary sources to describe the effect of one named and described genetic mutation on human health

Sickle Cell Anaemia

Point mutation occurs in gene for haemoglobin production one base is replaced by another

Down Syndrome

cause

- trisomy-21 when there is an additional copy of number 21 chromosome in the individual- can be result of non-disjunction when a gamete with two copies of number 21 chromosome (since

homologous chromosome pair did not separate during meiosis) fuses with a normal gamete- can be result of translocation of part of chromosome 21 to another chromosome, usually chromosome 14

or 15

effect

- lower than average mental ability- almond shaped eyes, shorter limbs, speech impairment, enlarged tongue, high risk of heart failure

impact on human health

- reduced mental capacity may be a limiting factor on development on individual in respect to social development, schooling and workforce – restrict opportunities

- physiotherapy needed as they have weakened muscles, shorter arms and legs- increased risk of several diseases such as cardiovascular failure

Outline the ability of DNA to repair itself

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


Mutations are quite common – caused by chemical mutagens, radiation and other mutagens - and so DNA needs to be able to repair itself to ensure no abnormal proteins are produced.

Over 130 genes are responsible for repairing DNA Copying errors are repaired by enzymes such as DNA polymerase when fixes incorrect bases based on

the undamaged strand. DNA repair genes stop the cell cycle while enzymes replace and repair damaged regions or bases

The DNA can be repaired in three main ways:

1) Damage reversal – Enzymes restore structure without breaking backbone2) Damage removal – who damaged section is cut out (e.g. by glycosylase enzymes) and the correct bases

are put back in3) Damage tolerance – where a method is found to cope with the damage, e.g. leaving a gap where the

damage is when replicating, although this can be dangerous if the cell divides

Not fixing damaged genes would lead to permanent mutations that can cause cancer and malfunction of cells

Describe the way in which transposable genetic elements operate and discuss their impact on the genome

Transposable genetic elements/transposons/jumping genes are sections of DNA that are not fixed and can move around among chromosomes.

Code for an enzyme that allows the movement or ‘jumping’ between chromsomes In bacteria, transposons within plasmids can move between bacteria. This means that antibiotic

resistance is not simply transferred by asexual reproduction, but it can spread to the genome of other bacteria

The impact on humans is not yet clear, although transposons could be inserted into another gene, causing mutation.

Distinguish between germ line and somatic mutations in terms of their effect on species

Germ line – cells which produce gametes

Mutations which affect sperm or ova Passed onto offspring Can have an effect on whole populations are it is passed on. Provides a source of variation which can

either be continued due to natural selection

Somatic – body cells

When mutation occurs, DNA is altered as with germ line cells and so gene expression is altered The different is somatic cells are not passed on to the next generation so affect only one organism

Explain using an appropriate example from agriculture why selective breeding has been practiced


Selective breeding improves quality and yield of production from farm animals and crops. It involves crossingvarieties to:

Combine favorable characteristics and allow better productivity, called hybrid vigour.

Can produce better nutritional value

Gain resistance to disease

Show tolerance to drought and cold

For example, Hereford cattle selectively bred with Brahman cattle to produce brahfords that have heat and tick

resistance and good growth rates and foraging skills.

Analyse and present information from secondary sources to trace the history of the selective breeding of one species for agricultural purposes and use available evidence to describe the series of changes that have occurred in the species as a result of this selective breeding

Wheat

1788- wheat farmed in Australia but can only be grown in areas with abundant rainfall and favourable soil- Australia’s poor soil and uncertain rainfall – insufficient crop yield- diseases such as stem rust would further destroy the crops

1889- Farrer began a wheat breeding program using varieties from all over the world- characteristics he sought to breed were rust resistance, early ripening and good bread-making properties

(high gluten levels)- wheat strains from India gave best early ripening characteristics and also had short stems and more grains

per wheat stalk- Farrer released his ‘Federation Wheat’ in 1902 which matured early and escaped rust-damage and had high

yield- soon, most wheat grown in Australia was Federation Wheat and it was able to withstand dry climate and

harsh heat of Australia

Fine wool merinosOver the past 300 years, farmers have selectively bred fine wool merinos. In doing so, they selected merinorams with favourable characteristics to sire offspring that will inherit these favourable characteristics. The aimof selectively breeding merinos is to produce tougher animals that produce wool of a higher quality andquantity.

Over the past 300 years: fibre strength increased fibre diameter and length decreased coat density increased animal hardiness increased

Describe the processes used in the cloning of an animal and analyse the methodology to identify ways in


which scientists could verify that the animal produced was a clone

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 it does 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.

Techniques to identify a clone:

DNA hybridisation can be used to tell whether two organisms are genetically identical with strands of each organisms DNA separated by heat and then one strand from each put together. Single strands matching up indicated a clone.

Fingerprinting and profiling looking at bands can be used to match DNA of two organisms The original and the clone organism can be determined using mitochondrial and chloroplast DNA which

will not be the same in each organism, despite cloning.

Describe what is meant by ‘gene cloning’ and give examples of the uses of gene cloning

Gene cloning: The process of selecting a particular gene, cutting it out of the DNA and inserting it into another organism where copies are made.

1) A gene is cut out of the chromosome using restriction enzymes. ‘Sticky ends’ are formed where cuts are made.

2) Circular DNA (plasmid) from a bacteria and cut using the same restriction enzyme3) The gene is mixed with the bacteria plasmid and DNA ligase is used as a ‘glue’ to allow the gene and

plasmid to recombine at matching sticky ends4) Plasmids are reinserted back into bacteria by adding calcium chloride to increase permeability of

bacteria membrane5) Bacteria reproduces and plasmids are cloned, cloning the recombinant genes6) The bacteria will also express the protein now introduced into its genome

Applications of recombinant genes

production of human insulin to treat diabetics (e.g. putting gene for insulin into E.coli) production of human growth hormone to treat stunted growth production of proteins that dissolve blood clots to treat heart attacks and other heart problems production of bacteria that can break down toxic wastes from oil spills

Distinguish between gene cloning and whole organism cloning in terms of the processes and products


Involves only part of an organisms DNA (i.e. a gene) Involves the whole genome (all DNA) from the parent

-Restriction enzymes cut gene-Gene placed in plasmid of bacteria-Bacteria copies gene

Several methods used-Somatic cell nuclear transfer where a somatic cell inplaced into an enucleated egg-Tissue cultures using meristematic tissue

Multiple copies of the single gene are produced. May also be used to produce proteins (e.g. insulin production) or for gene therapy.Larger numbers produced.

Produces whole offspring that are genetically identical.

Single or very few clones produced at once

Discuss a use of cloning in animals or plants that has possible benefits to humans

Use: Cloning plants for agriculture using tissue cultures

Tissue cultures are a way of cloning plants where a tissue sample (from the meristematic tissue) is taken and grown in a suitable environment such as soil or an agar plate. Benefits include:

Preserving biodiversity for future generations by cloning endangered species Cloning newly discovered or genetically engineered species to better propagate and spread superior

crops, e.g. BT cotton Increasing natural resources, e.g. cloning trees for furniture Genetically identical plants will produce a uniform product which is more desirable for consumers, e.g.

same colour on oranges Less costly and time consuming then continually selective breeding

Disadvantages lie in the fact that genetic diversity is decreased. If there is a selective pressure such as a disease or pest there may be no plants with resistance and so the whole population could be easily wiped out.

Identify the role of genes in embryonic development

As an embryo develops, genes differentiate (gain specific structures) and specialize (genes switched on toperform functions).

Formation of structures of the body is controlled by homeotic genes – activate or repress the expression of a large number of genes.

The zygote develops into a ball of cells, and different cells specialize to take different rolls as genes are switch on. This means they will produce different proteins and enzymes to alter cell metabolism and structure. In turn, different tissues develop.

Embryo develops due to different differentiation and specialization of cells

Examples include:

during embryonic development, genes for cellular respiration are active in all cells

in contrast, other genes are only switched on in certain specialised cells such as lens of the eye where genes that produce the protein crystallin are expressed (lens is made of crystalline)

pancreas is responsible for producing insulin which a few cells, islet cells have the gene for insulin production switched on

Summarise the role of gene cascades determining limb formation in birds and mammals


Gene cascade: a sequence in which genes are turned on and expressed.

Genes are turned on and off in a particular order and only in the correct cells

Protein produced by one gene acts as a transcription factor to turn on the next gene, and so on

Many genes are switched on in the right sequence and in the right places to form working parts

Limb Formation:

During embryonic development, tiny bulges bud out – the beginning of limbs. Position of limb buds is determined by HOX genes that start the gene cascade.

Genes at the start of the cascade are switched on and as each gene is expressed, the next is turned on.

In humans, limbs develop in weeks 5 and 6 and in a precise pattern: shoulders to fingers, thumb to little finger, back of the hand to the palm.

In chick embryos, buds become recognizable wings and legs by the 10th day.

HOX genes:

Homeobox genes (HOX) are master genes that produce proteins that activate or express a large number of genes for the formation of body structures (e.g. begin the gene cascade for limb formation)

HOX 9-13 control limb development in birds and mammals

describe the evidence which indicates the presence of ancestral vertebrate gene homologues in lower animal classes

Gene homologue: Similar DNA sequences in different organisms. Homeotic genes often are homologous,coding for the same function in many different organisms.

similar homologue genes have been found in every eukaryote studied including: invertebrates (eg. fruit flies and worms), vertebrates (eg. frogs, chickens and humans), yeasts and plants

they control the development of similar body parts in the developing embryos of many different species

presence of these similar DNA sequences in organisms suggests a common ancestry of all eukaryotic organisms

identify data sources gather process and analyse information from secondary sources and use available evidence to assess the evidence that analysis of genes provides for evolutionary relationships

Globin protein Globin proteins carry oxygen, e.g. haemoglobin Studies of DNA sequences of globin proteins across species such as insects and primates reveal similar

amino acid sequences that suggest an evolutionary relationship Differences can help map the evolutionary relationship, e.g. myoglobin in insects has alpha chains

whereas haemoglobin in mammals has alpha and beta chains.

DNA repair DNA repair genes are very similar in all organisms from yeasts to humans. Shows the repair process evolved early and has remained unchanged since then

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Genetics the Code Broken