Applications of reproduction and genetics

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Embryo Cloning

Allows farmers to make genetically identical inividuals to increase numbers of their animals...

1. Eggs taken from high yielding cows and fertilised in a petridish using sperm from the best bulls

2. This is known as In vitro fertilisation

3. The fertilised egg divides into a ball of cells, this young embyo is split into seperate cells

4. Each of these cells will develop into a new embryo genetically identical to the original.

4. These embyros are implanted into surrogates

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Cloning by nuclear transfer

Allows clones to be produced from one individual

1. Cells taken from somatic cell of donor and cultured in a medium which stops cell division

2. Unfertilised egg removed from recipient and nucleus removed, leaving egg cell without a nucleus

3. The donor and recipient cells are fused together using gentle electric pulse + allowed to divide

4. The developing embyro is implanted into the uterus of the surrogate

5. Born genetically identical to the orginal donor

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Advantages to cloning

  • Embryo cloning in farming allows for many genetically identical copies of animal to be produced
  • Desirable qualities to be preserved for furture generations (cloning preserves unique desirable features)
  • Cell culture is useful for production of cells in quantity eg. cancer cells for medical research, monoclonal antibodies, maintaining gentic stocks
  • Tissue culture- medium the cells grown in precisely controlled, produce tissue identical to adults
  • Tissue engineering - introducing living cells to grow on a framework or synthetic material to produce a tissue eg. skin tissue. This can be used for skin treatments like deep burns. Another practical application is blood vessle replacement, bone and cartilage repair and the treatment of degenerative nerve diseases. Stem cells are undifferentiated dividing cells that are found in selective tissure such as bone marrow. They are found in embryos at the early stages- Embyronic stem cells
  • Therapeutic stem cell cloning - cloned stem cells used to generate organs for transplant: prevents rejection and reduce organ shortages.
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Ethics and disadvantages to cloning

  • In mammals cloning is very expensive and unreliable
  • There may be the inadvertent selection of disadvantageous alleles
  • Progeny may show long-term/unforeseen effects such as premature ageing

ETHICS AND THE USE OF STEM CELLS

  • The supply of embyros comes from the surplus of embryos from fertility treatment. Once the stem cells are removed the embyros are destroyed- unethical to produce emyros that can never develop.
  • Some think the benefits outway the ethical concerns as it could treat Parkinson's disease, Alzheimer's disease, heart disease, liver diseases, diabetes, multiple scerosis and some cancers
  • Stem cells could also be sourced from bone marrow without consent- this has stricter rules
  • Slippery slope- devalue human life, conerns that other countries are cloning humans
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Micropropagation (plant tissue cultures)

Extremely cost effective way of producing large numbers of identical plants. Relies on the fact many plant cells are totipotent- Can develop into different cells under right conditions. At the tip of the rots and shoots are meristems and can grow into new identical plants.

  • Plant with desired characterists selected
  • Sterile scalpel used to remove meristem
  • Explants are placed onto sterile, areated nutrient medium eg. agar jelly
  •  
  • The callus is subdivided and each piece is allowed to differentiate into a plantlet
  • When they are big enough the plantlets are transplanted into sterile soil.
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Advantages and disadvantages of micropropagation

Benefits

  • Large numbers can be grown in sterile conditions to ensure greater survival rate
  • Less time consuming as it cuts out the requirment for pollination, seed production and seasonal restrictions on germination
  • Good quality stock selected- plant diseases can be eliminated
  • Crop is uniform to sells better
  • Large numbers stored in small area with reduced heating and lighting costs
  • Unique genotypes can be preserved
  • reduced space is required for transport

Costs

  • Sterile conditions must be maintained otherwise bacterial and fungal contamination may occur, loss of plants
  • Plants genetically unstable with increased rate of mutation leading to abnormality in the plantlets- regualr inspection needed to remove defects, thus labour costs higher than traditional methods
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Applications to the Human Genome Project

  • Enable scientists to know exactly which sections of DNA are responsable for inherited diseases- they do this by using gene probes to flag up and sections of DNA with a mutated sequence.
  • Another way is to compare the sample DNA sequence of a gene with the normal version gene.
  • Carrier screening- identify recessive genes, people may decide not to have children
  • Pre-implantation genetic diagnosis
  • Pre-natal diagnosis testing
  • New-born baby screening
  • Pre-symptomatic testing for predicting adult-onset disorders, genes are only a predispositional factor and therefore one can make sure their diet and environment doesnt increase the risk of the disorder expressing itself. These people can be targeted by health authorities and have regular screening and appropriate advice
  • Confirmation that an individual have suspected disease
  • Forensic/identity 
  • Design drugs that fit the specific protein it is aiming for or even the gene
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Advantages and limitations of gene testing

Advantages

  • Already dramatically improved lives- appropriate therapies and stopped people having children who would have a fatal disease

Disadvantages

  • Commercialised gene tests subject to debate- only give a probability to developing the disorder and people who get a postivie result may never actually develop the disease.
  • Possibility for lab errors- sample misidentification, contamination of chemicals used for testing
  • Tests have potential to provoke anxiety as there is a lack of cures and the risk for discrimination/social stigma could outway the benefits of using it. 
  • Social concerns... who should have the personal genetic information and how will it be used? Who owns and controls the genetic information? Should parents have the right to have their children tested for adult-onset diseases? Is there a danger of producing human clones? 
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Gene Therapy

Gene Therapy is a technique whereby a defective gene is replaced with a gene cloned from a healthy individual to provide a potential cure for a genetic disorder. 

Main problem is inserting the 'normal' genes into a person's cells and ensuring they function correctly once they get there. They use vectors to deliver the selected gene to the target cells.

2 ways to replace defective gene:

  • Somatic cell therapy- targets cells in the affected area. Not inherited
  • Germ-line therapy involves introducing correct genes into the egg and will enable genetic corrections to be inherited. 
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Cystic fibrosis

Cystis fibrosis is due to a defective autosomal recessive allele. Suffers produce thick, sticky mucus from the epithelial cells lining certain passage ways in the body. These secretions lead to problems:

  • Pancreatic duct becomes blocked, preventing pancreatic enzymes from reaching the duodenum and so food digestion is incomplete. 
  • The bronchioles and alveoli become clogged, causing congestion and problem with breathing. 
  • Mucus is difficult to move to leads to recurrent infections.

To relieve distress of breathing, frequent daily chest physiotherapy massage needed to keep airways open and children have large appetites to compensate for the lack of food absorbed. 

To inherit the disease both parents must be carriers, they can be identified by a blood test.The normal gene codes for the protein, cystic fibrosis trans-membrane regulator (CFTR), transports Cl ions out of cells into the mucus. Na ions follow out of the cells and water passes out of the cell by osmosis. This makes the mucus a watery consistancy. People with cystic fibrosis lack one amino acid and so cannot perform this transport function 

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Inserting genes into cells

The cloned genes that code for the CFTR protein are delivered to the epithelial cells in 2 ways:

USING LIPOSOMES

  • Wrapping the gene in lipid molecules that can pass through the membranes of lung cells 
  • An aerosol inhaler is used to add the non-defective gene to the epithelial cells of the lung
  • The liposomes fuse with the phospholipid bilar and the DNA enters the cell 

USING A VIRUS

  • Virus rendered harmless
  • Virus cultured in epithelial cells along with plasmids with the normal CFTR gene inserted
  • Gene becomes incorporated into the virus DNA
  • Virus is isolated and introduced into the patient by inhaler
  • Virus injects plasmid DNA into the epithelial cells of the lungs
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How effective is gene therapy?

  • limited success becauses it is only short lived and may need to be repeated every 30 days
  • Only small proportion of the introduced genes are expressed
  • May have immune response

However the benefits outway the disadvantages as it gives a child with an inherited diseases the chance at normal life and prevent the development of cancer in an inividuals are goals that medical science must aspire to. 

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Genetic counselling and genetic screening

If a family has a history of a genetic defect, unaffected members can consult a genetic counsellor for advice on the risk of bearing an affected child. Once the risk of passing on a defective allele is established the parents can have a test to see whether to carry on with the preganancy. 

  • Blood test- there is just a simple blood test for cystic fibrosis
  • Amniocentesis- withdrawing some amniotic fluid at 15-20 weeks which contains some cells that have floated away from the embyo. These cells are analysed
  • Chorionic villus sampling- early in pregnancy (8-20 weeks) tiny samples of foetal tissue are withdrawn from the uterus and cells are cultured and analysed. 
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Genetic engineering

Genetic engineering allows genes to be manipulate, altered and transferred from one organism to another. Applications:

  • Genes in bacteria to make useful products such as insuline
  • Genes in plants and animals so that they acquire new characterisics eg. resistance to disease. 
  • Genes in humans so that they no longer suffer from genetic diseases such as cystic fibrosis. 

The process of producing a protein using DNA technology and cloning:

  • Isolation if the DNA fragments
  • Insertion of the DNA fragment into a vector 
  • Transfer of DNA into suitable host cells 
  • Identification of the host cells that have taken up the gene by the use of gene markers
  • Clonning of the host cells
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DNA identification and isolation

Gene is identified using a gene probe which is a specific segment of single-strand DNA that is complementary to a desired gene. 

RESTRICTION ENDONUCLEASE

The gene is then isolated using restriction endonuclease which cuts the DNA into small pieces allowing individual genes to be identified. The enzyme cuts the DNA between specific base sequences which the enzyme recognises. They create sticky ends

REVERSE TRANSCRIPTASE

Functional mRNA will be present in large numbers in certain places where the protein needed is being secreted and is extracted. Addition of reverse transcriptase, made by a group of viruses called retreoviruses, is used to make a DNA copy of the mRNA. This single strand of DNA is called copy DNA or cDNA. Many copies of cDNA are made. The addition of DNA polymerase converts this to a double strand for insertion into a plasmid. 

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