5.11.1 Human Genome Project

·         Genetic make-up of an organism or an individual lies in the DNA sequences.

·         DNA sequences are different of two different individuals.

·         The Human Genome Project ( H.G.P.) was an international scientific research project with a primary goal to determine the sequence of chemical base pairs which make up DNA and to identify and map the approximately 20,000–25,000 genes of the human genome from both a physical and functional standpoint.

·         The first available assembly of the genome was completed in 2000 by the UCSC Genome Bioinformatics Group, composed of Jim Kent , Patrick Gavin, Terrence Furey, and David Kulp.

·         The project began in 1990, initially headed by James D. Watson at the U.S. National Institutes of Health. A working draft of the genome was released in 2000 and a complete one in 2003, with further analysis still being published.

·         The human genome project (HGP), a publicly funded project led by Dr. Francis Collins of the National Institute of Health (NIH) of the USA.

·         Celera Genomics Corporation a private research effort led by Dr. Craig Venter began in 1990 and completed in June 2000.

·         An ambitious international Human Genome Project began in 1990. The goals of this project are:

§         To develop ways of mapping the human genome at increasing fine level of precision.

§         To store this information in databases and develop tools for data analysis, and

§         To address the ethical, legal and social issues that may arise from this project.

·         The mapping of human genes is an important step in the development of medicines and other aspects of health care.

·         While the objective of the Human Genome Project is to understand the genetic makeup of the human species, the project also has focused on several other nonhuman organisms such as E. coli, the fruit fly, and the laboratory mouse.

·         The HGP originally aimed to map the nucleotides contained in a haploid reference human genome.

·         The "genome" of any given individual (except for identical twins and cloned organisms) is unique; mapping "the human genome" involves sequencing multiple variations of each gene.

5.11.1.1 Salient Features of Human Genome

·         The human genome is the genome of Homo sapiens, which is stored on 23 chromosome pairs.

·         Twenty-two of these are autosomal chromosome pairs, while the remaining pair is sex-determining.

·         The haploid human genome occupies a total of just over 3 billion DNA base pairs.

·         The Human Genome Project (HGP) produced a reference sequence of the euchromatic human genome, which is used worldwide in biomedical sciences.

·         The haploid human genome contains ca. 23,000 protein-coding genes, far fewer than had been expected before its sequencing.

·         In fact, only about 1.5% of the genome codes for proteins, while the rest consists of non-coding RNA genes, regulatory sequences, introns, and "junk" DNA.

·         The estimate of the number of human genes has been repeatedly revised down from initial predictions of 100,000 or more as genome sequence quality and gene finding methods have improved.

·         The number of human genes seems to be less than a factor of two greater than that of many much simpler organisms, such as the roundworm and the fruit fly.

·         Human cells make extensive use of alternative splicing to produce several different proteins from a single gene, and the human proteome is thought to be much larger than those of the aforementioned organisms.

·         Most human genes have multiple exons, and human introns are frequently much longer than the flanking exons.

·         Human genes are distributed unevenly across the chromosomes. Each chromosome contains various gene-rich and gene-poor regions, which seem to be correlated with chromosome bands and GC-content.

·         The significance of these nonrandom patterns of gene density is not well understood.

·         In addition to protein coding genes, the human genome contains thousands of RNA genes, including tRNA, ribosomal RNA, microRNA, and other non-coding RNA genes.

Human Genome

·         First analysis of the Human Genome-Highlights

§         There are approximately 30,000 genes in human being.

§         All human races are 99.9% alike.

§         Most genetic mutation occurs in the male of species.

§         Genes function as complex networks, rather than single entities producing specific proteins.

§         Human being has a greater percentage for junk DNA than after species.

·         Revelations of Genome

The Human gene count is

·         around the same in mice. Nine-tenths of our genes are identical to that of the mice.

·         more than twice as many genes as fruitfly Drosophila melanogaster

·         only six times more genes than bacterium, Escherichia coli.

·         Few other facts are

§         Different types of genes in humans differ considerably in length usually in thousands of base pairs.

§         β - globin and insulin genes are made up of less than 10 kilobase pairs, longest gene responsible for Duchenne muscular dystrophy on ‘X’ chromosome is make up of 2400 kilobase pairs.

§         Lily (flowering plant) bears 18 times more DNA than Humans, but produces less proteins than humans (i.e., large amount of genes is split by long non-coding introns. Note more than 2 percent of genome acts as coding exons).

·         Prospects and implications of human genome

§         Nearly more than 1200 genes have been identified for human disease like cardiovascular ailments neurological disorders like Alzheimer’s disease and even cancers.

5.11.1.2 Applications and Future Challenges

·                     Genomics has the following applications

(i)        enhancing basic understanding,

(ii)      providing information that will help to prevent inherited diseases, and

(iii)     treatment of genetic disorders through gene therapy.

·         Production of transgenic organisms is also an application of genomics.

Transgenic Organisms

·         The organisms, which contain functional genes experimentally introduced by genetic engineering from another species, are called transgenic organisms or Transgenics, or Genetically modifies organisms (GMOs). The foreign gene alters the host cell genetically, and is termed transgene. The production of transgenic organisms is known as transgenesis or Transfection.

5.11.2 Forensic Science

·         Forensic science (often shortened to forensics) is the application of a broad spectrum of sciences to answer questions of interest to a legal system.

·         This may be in relation to a crime or a civil action. Besides its relevance to a legal system, more generally forensics encompasses the accepted scholarly or scientific methodology and norms under which the facts regarding an event, or an artifact, or some other physical item (such as a corpse) are ascertained as being the case.

·         In that regard the concept is related to the notion of authentication, where by an interest outside of a legal form exists in determining whether an object is what it purports to be, or is alleged as being.

·         The word forensic comes from the Latin adjective forensis, meaning "of or before the forum". In Roman times, a criminal charge meant presenting the case before a group of public individuals in the forum.

·         Both the person accused of the crime and the accuser would give speeches based on their side of the story.

·         The individual with the best argument and delivery would determine the outcome of the case.

·         This origin is the source of the two modern usages of the word forensic – as a form of legal evidence and as a category of public presentation.

·         In modern use, the term "forensics" in place of "forensic science" can be considered incorrect as the term "forensic" is effectively a synonym for "legal" or "related to courts". However, the term is now so closely associated with the scientific field that many dictionaries include the meaning that equates the word "forensics" with "forensic science".

5.11.3 DNA Finger Printing

·         DNA fingerprinting is a modern technique that compares sets of DNA by locating identical sequences of nucleotides, often for purposes of forensic identification. It is also known as DNA profiling or DNA typing. It was invented by Sir Alec Jeffreys (1984), at Leicester University, United Kingdom.

·         Dr. V.K. Kashyap and Dr. Lalji Singh started the finger printing technology in India.

5.11.3.1 Base of DNA Fingerprinting

·         It is based on the fact that DNA of one individual is about 90% identical to the DNA of another individual, but there is 10% of the DNA that is different. This 10% of the total DNA does not code for protein and carries some specific short sequences of about 10-100 nucleotide pairs. These specific sequences are found at many places throughout the length of DNA. The number of repeats is very specific in each individual. Such polymorphic genetic loci are usually called simple tandem repeats (STRs) or microsatellite. These tandem repeats of short sequence are called variable number tandem repeats (VNTRs). These repeats are inherited form the parents, and are used s genetic markers in a personal identity test.

5.11.3.2 Sources of DNA for Fingerprinting

·         DNA for fingerprinting test may be obtained from blood or semen stains on clothes or other surfaces, saliva residue on cigarette buts, vaginal swab or even a single hair.

5.11.3.3 Procedure for DNA Fingerprinting

·         DNA molecules are isolated from the source by using specific techniques. If DNA is in poor condition, the particular STRs may be amplified by using polymerase chain reaction (PCR).

·         DNA molecules are cut into fragments at specific sites with the help of a restriction endonuclease enzyme. These DNA fragments contain the VNTRs.

·         DNA fragments are then store out according to their length on agarose gel slab by the technique called electrophoresis. The fragments get arranged along the gel according to their length and electric charges.

·         The isolated DNA fragments in the gel are copied onto a nylon paper by another technique named Southern blotting (E. Southern, 1975).

·         Special DNA probes are prepared in the laboratory, which contain repeated sequences of nucleotides complementary to those on VNTRs. These DNA probes are made radioactive (P³²). The radioactive DNA-probes bind to the repeat sequences on the nylon paper. This is called hybridization.

·         An X-ray film is exposed to the nylon paper to mark the places where the radioactive DNA probes have bound to the DNA fragments. These places are marked as dark bands when X-ray film is developed. This process is called autoradiography.

·         The dark bands on X-ray film represent the DNA fingerprints (also called as DNA profiles). The pattern of bands obtained on the film is 100 percent unique for each person, except for identical twins who would have the same pattern.

5.11.3.4 Application of DNA Finger Printing

·                     DNA fingerprinting is used in

(i)        the study of breeding patterns of animals facing the danger of extinction,

(ii)      settling paternity dispute,

(iii)     detecting crime,

(iv)    tracing path of hereditary diseases,

(v)     identification of plant varieties for patent, parentage and trait marker purpose, etc.

·         The DNA fingerprinting has been accepted as evidence in the law courts since 1986. Some argue that DNA evidence is more are reliable than an eyewitness.

·         In India, Center for Cell and Molecular Biology (CCMB), Hyderabad has the advanced laboratory for DNA fingerprinting. All disputes of rape, murder, parentage, etc, are sent to this lab only.

5.11.4 Human Health Care

·         Health is the general condition of a person in all aspects. It is also a level of functional and/or metabolic efficiency of an organism, often implicitly human.

·         At the time of the creation of the World Health Organization (WHO), in 1948, health was defined as being "a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity."

·         Overall health is achieved through a combination of physical, mental, emotional, and social well-being, which, together is commonly referred to as the Health Triangle.

·         Health care is the prevention, treatment, and management of illness and the preservation of mental and physical well being through the services offered by the medical, nursing, and allied health professions.

·         Genetics, which is the branch of biology that studies heredity, concerns the biochemical instructions that convey information from generation to generation.

·         In order to appreciate the role of genetics in health and illness, it is important to understand the interaction of genes, chromosomes, and genomes and to learn how deoxyribonucleic acid (DNA) functions as the information molecule of living organisms.

·         Humans have 46 chromosomes arranged in 23 pairs, and the human genome contains about 30,000 genes and 600,000 pairs of DNA.

·         Changes in the number, size, shape, or structure of chromosomes can result in a variety of physical and mental abnormalities and diseases.

·         For inheritance of simple genetic traits, the two inherited copies of a gene determine the phenotype (the observable characteristic) for that trait. When genes for a particular trait exist in two or more different forms that may differ between individuals and populations, they are called alleles.

·         For example, brown and blue eye colors are due to different alleles for eye color. For every gene, the offspring receives two alleles, one from each parent. The combination of inherited alleles is the genotype of the organism, and its expression—the observable characteristic—is its phenotype.

·         For many traits the phenotype is a result of an interaction between the genotype and the environment. Some of the most readily apparent traits in humans, such as height, weight, and skin color, result from interactions between genetic and environmental factors. In addition, there are complex phenotypes that involve multiple gene-encoded proteins and the alleles of these particular genes are influenced by other factors, either genetic or environmental. So while the presence of certain genes indicates susceptibility or likelihood to develop a certain trait, it does not guarantee expression of the trait.

5.11.5 Gene Therapy

‘Gene therapy is the insertion of genes into an individual’s cells and tissues to treat a disease, such as a hereditary disease in which a deleterious mutant allele is replaced with a functional one.’

·         Although the technology is still in its infancy, it has been used with some success. Scientific breakthroughs continue to move gene therapy toward mainstream medicine.

·         Gene therapy may be classified into the following types-

i. Germ Cell gene therapy

§         In the case of germ line gene therapy, germ cells, i.e., sperm or eggs, are modified by the introduction of functional genes, which are ordinarily integrated into their genomes.

§         Therefore, the change due to therapy would be heritable and would be passed on to later generations.

§         This new approach, theoretically, should be highly effective in counteracting genetic disorders and hereditary diseases.

§         However, many jurisdictions prohibit this for application in human beings, at least for the present, for a variety of technical and ethical reasons.

ii. Somatic Cell gene therapy In the case of somatic gene therapy, the therapeutic genes are transferred into the somatic cells of a patient. Any modifications and effects will be restricted to the individual patient only, and will not be inherited by the patient’s offspring or later generations.

Broad methods –

§         There are a variety of different methods to replace or repair the genes targeted in gene therapy.

§         A normal gene may be inserted into a nonspecific location within the genome to replace a nonfunctional gene. This approach is most common.

§         An abnormal gene could be swapped for a normal gene through homologous recombination.

§         The abnormal gene could be repaired through selective reverse mutation, which returns the gene to its normal function.

§         The regulation (the degree to which a gene is turned on or off) of a particular gene could be altered.

§         Spindle transfer is used to replace entire mitochondria that carry defective mitochondrial DNA.

·         The main emphasis of gene therapy is for correcting single gene defects (mutations), such as cystic fibrosis and haemophilia which have been observed in families by their Mendelian pattern of inheritance.

·         In present time, most genetic diseases have no effective treatment, so gene therapy could offer hope for several people.

·         Somatic cell gene therapy for complex multifactorial disease, e.g., Parkinson’s disease, cancer must be a long way off.

·         In many of these diseases, there can be several genes involved as well as an interaction with environmental factors.

·         Gene therapy is being employed to correct certain disease like SCID (Severe Combined Immune Deficiency Syndrome) with variable degrees of success.

·         This therapy is at experimental stage and attempts are being made to use this therapy for curing diseases like cancer, heart attack, haemophilia, Parkinson’s disease etc.