BIOLOGY: CLONING
Overview- Cloning is the process by which genetically identical individuals are produced
- Cloning happens in nature by the biological mechanisms of asexual reproduction in bacteria, insects and plants
- Cloning can also be performed artificially by copying fragments of DNA (molecular cloning) or cells (cell cloning) or organisms
- Mammals, which reproduce sexually, cannot clone naturally. Mammals inherit genetic material half each from both parents, meaning that the progeny is never an identical replica of the parent. Natural clones in mammals are confined to the production of identical twins
- The first vertebrate to be cloned was a tadpole by Robert Briggs (USA) and Thomas King (USA) in 1952
Cloning in plants
- Plants have been clone for a long time.
- Grafting is a form of plant cloning
- Many horticulture plants are cloned, having been derived from a single individual
- Examples of plant cloning include carrots, tobacco, potato, banana
Cloning in animals
- Cloning of animals is based on a technique known as “somatic cell nuclear transfer”.
- Nuclear transfer involves fusing two cells together – a donor cell containing all its DNA, and egg cell with all its DNA removed
- The two cells are fused with an electric pulse and the resulting enucleated egg is implanted in the mother
Dolly the Sheep
- Dolly, a Finn Dorset ewe, was the first mammal to be successfully cloned from an adult cell
- Dolly was cloned by Ian Wilmut and Keith Campbell at the Roslin Institute in Edinburgh (Scotland)
- Dolly was born in 1996 and lived for six years
- The donor cell for Dolly was taken from a mammary gland.
- Production of a healthy clone proved that a cell from a specific part of the body could recreate a whole individual
Some animals that have been cloned
See here for the full list cloned animals.
| Cloned animal | When | Where | By whom | Notes |
| Tadpole | 1952 | USA | Robert Briggs, Thomas King | |
| Carp (fish) | 1963 | China | Tong Dizhou | |
| Mice (first cloned mammal) | 1986 | Soviet Union | Chaylakhyan, Veprencev, Sviridova, Nikitin | First cloned mammal |
| Sheep (first cloned mammal from adult cell) | 1996 | Britain | Ian WIlmut, Keith Campbell | First cloned mammal from adult cell |
| Rhesus monkey (named Tetra) | 2000 | It was named Tetra | ||
| Gaur (Asian Ox) | 2001 | USA | Jonathan Hill, Philip Damiani | Named Noah First endangered species to be cloned |
| Cat | 2001 (Copycat) 2004 (Little Nicky) | USA | Copycat was the first cloned pet Little Nicky was the commercially produced cat clone | |
| Mule (named Idaho Gem) | 2003 | USA | Gordon Woods, Dirk Vanderwall | First clone in horse family |
| Horse (named Prometea) | 2003 | Italy | Cesare Galli | First cloned horse First animal to be born from and carried by its cloning mother |
| Water buffalo (called Samrupa) | 2009 | India | S K Singla and others at Karnal National Dairy Research Institute | First cloned buffalo Died 5 days after birth due to lung infection |
| Camel (called Injaz) | 2009 | Dubai | Nisar Ahmad Wani | First cloned camel |
BIOLOGY: GENETIC ENGINEERING
Overview- Genetic engineering refers to the direct manipulation of an organism’s genes
- Genetic engineering is also referred to as recombinant DNA technology, genetic modification and gene splicing
- Genetic engineering uses cloning and transformation of molecules to alter the structure and characteristics of genes
- Examples of genetic engineering include improved crop technologies, synthetic hormones, and creation of experimental mice
Process of genetic engineering
The process of genetic engineering has five main steps:
- Isolation of the genes of interest
- Insertion of the genes into a transfer vector
- Transfer of the vector to the organism to be modified
- Transformation of the cells of the organism
- Selection of the genetically modified organisms from those that have not been successfully modified
Applications of genetic engineering
- The first genetically engineered medicine was synthetic insulin
- Genetic engineering has been used to produce vaccines for hepatitis B
- Creation of genetically modified foods such as soybean, corn, canola and cotton seed oil. GM foods have higher resistance to pests, bacterial/fungal infections, higher yield and higher nutritional value
- Gene therapy using viruses to treat severe combined immunodeficiency (SCID)
- Using genetically modified virus to construct environment friendly lithium-ion battery
- Using human eggs from a second mother to allow infertile women with genetic defects in their mitochondria to have children
- Artificial DNA, called Synthetic Organism (SO-1), with unknown functions has been created
Milestones in genetic engineering
- 1953: James Watson (USA) and Francis Crick (Britain) discover structure of DNA. They win Nobel in Physiology or Medicine in 1979
- 1973: Stanley Cohen (USA) and Herbert Boyer (USA) develop a technique to clone segments of DNA molecules
- 1976: Genentech, the first company dedicated to producing genetically engineered products is established in San Francisco. It was founded by Herbert Boyer and Robert Swanson
- 1979: Genetic engineering used to synthesize insulin
- 1981: scientists at Ohio university transfer genes from other organisms into mice
- 1990: Human Genome Project launched
- 1990: first gene therapy experiment performed on a four-year old girl with adenosine deaminase deficiency. Developed by French Anderson
- 1996: a yeast known as Saccharomyces cerevisiae is the first eukaryotic genome to be sequenced by more than 100 labs collaboratively around the world
- 2003: Human Genome Project announces complete mapping of human genome
GENETICALLY MODIFIED FOODS
- BT-Cotton
- BT-Cotton is a genetically modified variety of cotton into which Cryiae gene from the bacillus thuriegenois bacteria have been introduced
- This gene produces a toxin called BT-Toxin in every part of the plant thereby destroying the dreaded cotton pest Bollworm
- This technology was developed by US seed company Monsanto
- However, concerns include evolution of super-pests with higher levels of resistance, destruction of agriculturally beneficial organisms like bees, soil microflora etc
- BT-Cotton is a genetically modified variety of cotton into which Cryiae gene from the bacillus thuriegenois bacteria have been introduced
- Terminator gene
- Terminator gene is a seed variety developed using genetic engineering
- It causes the seed to self-destruct after it has been used to raise the first generation of crops
- This is done in order to prevent farmers from raising subsequent generations of crops without paying royalties
- Concerns include this self-destruct gene may be transferred to other plants by cross-pollination leading to extinction of traditional agricultural production
- It is also known as Genetic Use Restriction Technology (GURT) and was developed by the US Department of Agriculture in conjunction with the Delta and Pine Land Co.
- Golden rice
- Type of rice crop provided with a gene to develop Beta-Carotene
- This helps production of vitamin A in the body
- This helps fight vitamin A deficiency, the primary cause of childhood blindness
- Beta-carotene gives rice a yellow colour and hence is called Golden Rice
- Created by Swiss Federal Institute of Technology
- GM Cabbage
- Cabbage that will resistant to attack of Diamond Back Moth
- Developed by Indian Agricultural Research Institute (New Delhi)
BIOLOGY: GENETIC DISORDERS
About genetic disorders
Huntington's disease is inherited in the autosomal dominant fashion
- Genetic disorders are disorders that are passed on from generation to generation
- They are caused by abnormalities in genes or chromosomes
- Some genetic disorders may also be influenced by non-genetic environmental factors. Eg: cancer
- Most genetic disorders are relatively rare and only affect one person in thousands or millions
- To recollect, males have XY chromosome pairs while females have XX pairs
Single Gene Disorders
- Single gene disorders result from the mutation of a single gene
- They can be passed onto subsequent generations in multiple ways
- Single gene disorders include sickle cell disease, cystic fibrosis Huntington disease
Multiple gene disorders
- Multiple gene disorders result from mutation on multiple genes in combination with environmental factors
- They do not have a clear pattern of inheritance, which makes it difficult to assess risk of inheriting a particular disease
- Examples include heart disease, diabetes, hypertension, obesity, autism
TYPES OF SINGLE GENE GENETIC DISORDERS
- Autosomal dominantSickle cell disease is inherited in the autosomal recessive pattern
- Only one mutated copy of the gene is necessary for inheritance of the mutation
- Each affected person usually has one affected parent
- There is a 50% chance that the child will inherit the mutated gene
- Autosomal dominant disorders usually have low penetrance i.e. although only one mutated copy is needed, only a small portion of those who inherit that mutation will develop the disorder
- Eg: Huntington’s disease, Marfan syndrome
- Only one mutated copy of the gene is necessary for inheritance of the mutation
- Autosomal recessive
- Two copies of the gene must be mutated for a person to be affected
- An affected person usually has unaffected parents who each have one mutated gene
- There is a 25% chance that the child will inherit the mutated gene
- Eg: Cystic fibrosis, sickle cell disease, Tay-Sachs disease, dry earwax, Niemann-Pick disease
- Two copies of the gene must be mutated for a person to be affected
- X-linked dominant
- X-linked dominant disorders are caused by mutations on the X chromosome
- Males and females are both affected by such disorders. However, males are affected more severely
- For a man with a X-linked dominant disorder, his sons will all be unaffected (since they receive their father’s Y chromosome) while his daughters will all be affected (since they receive his X chromosome)
- A woman with a X-linked dominant disorder has a 50% chance of passing it on to progeny
- Eg: Hypophosphatemic rickets, Rett syndrome, Aicardi syndrome
- X-linked recessiveX-linked recessive with a carrier mother
- Caused by mutations on the X-chromosome
- Males are affected more frequently than females
- The sons of a man affected by a X-linked recessive disorder will not be affected, while his daughters will carry one copy of the mutated gene
- The sons of a woman affected by a X-linked recessive disorder will have have a 50% chance of being affected by the disorder, while the daughters of the woman have a 50% chance of becoming carriers of the disorder
- Eg: colour blindness, muscular dystrophy, hemophilia A
- Y-linked disorders
- Caused by mutations on the Y chromosome
- Y chromosomes are present only in males
- The sons of a man with Y-linked disorders will inherit his Y chromosome and will always be affected while the daughters will inherit his X chromosome and will never be affected
- Eg: male infertility
- Mitochondrial disorders
- These disorders are caused by mutations in the mitochondrial DNA
- Only mothers can pass on mitochondrial disorders to children, since only egg cells (from the mother) contribute mitochondria to the developing embryo
- Eg: Leber’s Heriditary Optic Neuropathy
BIOLOGY: GENETICS
History of genetics research
- The father of genetics is Gregor Mendel (Austria-Hungary). In 1866 he published the principle known as Mendelian Inheritance which described the concept of inheritance between parent organisms and offspring
- In 1869 Friedrich Miescher (Switzerland) discovered DNA
- 1880: Walther Flemming (Germany) describes division of chromosomes
- 1933: Jean Brachet (Belgium) establishes DNA is found in chromosomes and RNA in cell cytoplasm
- 1944: Oswald Theodore Avery, Colin McLeod, Maclyn McCarty (US) identify DNA as genetic material
- 1953: James Watson and Francis Crick (US) establish double helix structure of DNA. They win the Nobel Prize in Physiology or Medicine in 1962 for this discovery
- 1968: Hargobind Khorana, Robert Holley and Marshall Nirenberg (US) demonstrate the role of RNA in protein synthesis. Nobel in Medicine 1968
- 1977: Frederick Sanger (UK) sequences DNA for the first time. He produce the entire genome of bacteriophage X174. Nobel in Chemistry in 1980
- 1983: Kary Mullis (US) discovers polymerace chain reaction enabling easy amplification of DNA. Nobel in Chemistry 1993
- 1995: The genome of Haemophilus influenzae is the first genome of a living organism to be sequenced
- 2001: First draft sequence of the human genome
- 2003: Human Genome Project successfully completed
- DNA (deoxyribonucleic acid) is the basis for genetic inheritance. However, certain viruses use RNA for genetic information
- DNA is composed of a chain of nucleotides. There are four types of nucleotides: adenine (A), cytosine (C), guanine (G), thymine (T)
- DNA usually exists in a double-helix structure molecule
- Each nucleotide in one strand of the double-helix pairs with a particular partner nucleotide in the other strand. A pairs with T and C pairs with G
- Genes are regions within DNA. Genes are arranged in long chains of DNA molecules. These chains are called chromosomes
- Eukaryotic organisms have DNA arranged in multiple such chromosomes. Bacteria have only one chromosome
- The combined DNA sequence of all chromosomes is called the genome. This contains all hereditary information of that organism
- Haploid organisms have only copy of each organism. Eg: male bees, wasps, ants
- Diploid organisms have two copies of each chromosome. Eg: most plants and animals (including humans). However, in male humans the sex-linked X and Y chromosomes exist only as a single copy.
- Male: XY, Female: XX
- The Human Genome Project was an international scientific effort to determine the complete genetic code of human beings
- Launched in 1990, complete results published in 2003
- Performed by scientists from US, UK, Canada and New Zealand, lead by University of California Santa Cruz
- Key findings of the project include
- There are approximately 25000 genes in human beings
- All human races are 99.99% alike genetically
- Most genetic mutation occurs in male. Thus males are responsible for genetic evolution and for genetic disorders
- Human Genome Project mapped nucleotides in haploid sequences. Efforts are currently underway to map diploid sequences as well. Eg: International HapMap Project, Personal Genome Project
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