The management of genetic disease can be divided into counseling, diagnosis, and treatment. In brief, the fundamental purpose of genetic counseling is to help theindividual or family understand their risks and options and to empower them to make informed decisions. Diagnosis of genetic disease is sometimes clinical, basedon the presence of a given set of symptoms, and sometimes molecular, based on the presence of a recognized gene mutation, whether clinical symptoms are present or not. The cooperation of family members may be required to achieve diagnosis for a given individual, and, once accurate diagnosis of that individual has been determined, there may be implications for the diagnoses of otherfamily members. Balancing privacy issues within a family with the ethical need to inform individuals who are atrisk for a particular genetic disease can become extremely complex. Although effective treatments exist for some genetic diseases, for others there are none. It is perhaps this latter set of disorders that raises the most troubling questionswith regard to presymptomatic testing, because phenotypically healthy individuals can be put in the position ofhearing that they are going to become ill and potentially die and that there is nothing they or anyone else can do to stop it. Fortunately, with time and research, this set of disorders is slowly becoming smaller.
Tuesday, 12 April 2011
DNA Fingerprinting
DNA fingerprinting, also known as DNA typing, is a method of isolating and making images of sequences of DNA. The technique was developed in 1984 by the British geneticist Alec Jeffreys, after he noticed the existence of certain sequences of DNA (called minisatellites) that do not contribute to the function of a gene but are repeated within the gene and in other genes of a DNA sample. Jeffreys also determined that each organism has a unique pattern of these minisatellites, the only exception being multiple individuals from a single zygote (e.g., identical twins). The procedure for creating a DNA fingerprint consists of first obtaining a sample of cells containing DNA (e.g., from skin, blood, or hair), extracting the DNA, and purifying it. The DNA is then cut at specific points along the strand with substances called restriction enzymes. This produces fragments of varying lengths that are sorted by placing them on a gel and then subjecting the gel toan electric current (electrophoresis): the shorter the fragment the more quickly it will move toward the positive pole (anode). The sorted, double-stranded DNA fragments are then subjected to a blotting technique in which they are split into single strands and transferred to a nylon sheet. The fragments undergo autoradiography in which they are exposed to DNA probes—pieces of synthetic DNA that have been made radioactive and that bind to the minisatellites. A piece of X-ray film is then exposed to the fragments, and a dark mark is produced at any point where a radioactive probe has become attached. The resultant pattern of these marks can then be analyzed. An early use of DNA fingerprinting was in legal disputes,notably to help solve crimes and to determine paternity. The technique was challenged, however, overconcerns about sample contamination, faulty preparation procedures, and erroneous interpretation of the results. Efforts were made to improve reliability, and today the technique has been refined through the use of more specific and more sensitive probes and better blotting membranes. It also has been recognized that DNA fingerprinting, similar to other DNA analysis techniques, is limited by the quality of the sample obtained. DNA samples that are degraded or collected postmortem typicallyproduce less reliable results than do samples that are obtained from a living individual. If only a small amount of DNA is available for fingerprinting, PCR may be used to create thousands of copies of a DNA segment. Once an adequate amount of DNA has been produced, the exact sequence of nucleotide pairs in a segment of DNA can be determined using one of several biomolecular sequencing methods. Automated equipment has greatly increased the speed of DNA sequencing and has made available many practical applications, including pinpointing segments of genes that cause genetic diseases, mapping the human genome, engineering drought-resistant plants, and producing biological drugs from genetically altered bacteria.
Genetic codes
The genetic code is the set of rules by which a gene is translated into a functional protein. Each gene consists of a specific sequence of nucleotides encoded in a DNA (or sometimes RNA) strand; a correspondence between nucleotides, the basic building blocks of genetic material, and amino acids, the basic building blocks of proteins, must be established for genes to be successfully translated into functional proteins. Sets of three nucleotides, known as codons, each correspond to a specific amino acid or to a signal; three codons are known as "stop codons" and, instead of specifying a new amino acid, alert the translation machinery that the end of the gene has been reached. There are 64 possible codons (four possible nucleotides at each of three positions, hence 43 possible codons) and only 20 standard amino acids; hence the code is redundant and multiple codons can specify the same amino acid. The correspondence between codons and amino acids is nearly universal among all known living organisms.
Genetic Testing
In the case of genetic disease, options often exist for presymptomatic diagnosis—that is, diagnosis of individuals at risk for developing a given disorder, even though at thetime of diagnosis they may be clinically healthy. Options also may exist for carrier testing, studies that determine whether an individual is at increased risk of having a child with a given disorder, even though he or she personally may never display symptoms. Accurate predictive information can enable early intervention, which often preventsthe clinical onset of symptoms and the irreversible damage that may have already occurred by waiting for symptoms and then responding to them. In the case of carrier testing, accurate information can enable prospective parents to make more-informed family- planning decisions. Unfortunately, there can also be negative aspects to early detection, including such issues as privacy, individual responses to potentially negative information, discrimination in the workplace, or discrimination in access to or cost of health or life insurance. While some governments have outlawed the use of presymptomatic genetic testing information by insurance companies and employers, others have embraced it as a way to bring spiraling health-care costs under control. Some communities have even considered instituting premarital carrier testing for common disorders in the populace. Genetic testing procedures can be divided into two different groups: (1) testing of individuals considered atrisk from phenotype or family history and (2) screening of entire populations, regardless of phenotype or personal family history, for evidence of genetic disorders commonin that population. Both forms are currently pursued in many societies. Indeed, with the explosion of informationabout the human genome and the increasing identification of potential “risk genes” for common disorders,such as cancer, heart disease, or diabetes, the role of predictive genetic screening in general medical practice is increasing.
Study of Human Genetics
Some geneticists specialize in the hereditary processes of human genetics. Most of the emphasis is on understanding and treating genetic disease and genetically influenced ill health, areas collectively known as medical genetics. One broad area of activity is laboratory research dealing with the mechanisms of human gene function and malfunction and investigating pharmaceutical and other types of treatments. Since there is a high degree of evolutionary conservation between organisms, research on model organisms—such as bacteria, fungi, and fruit flies (Drosophila)—which are easier to study, often provides important insights into human gene function. Many single-gene diseases, caused by mutant alleles of a single gene, have been discovered. Two well-characterized single-gene diseases include phenylketonuria (PKU) and Tay-Sachs disease. Other diseases, such as heart disease, schizophrenia, and depression, are thought to have morecomplex heredity components that involve a number of different genes. These diseases are the focus of a great deal of research that is being carried out today. In addition,abnormalities in chromosomes have been identified by studies employing techniques such as chromosomal banding. Individual chromosomes are identified by the banding patterns revealed by different staining techniques.Segments of chromosomes or chromosomes that are aberrant in number and morphology may be precisely identified.Another broad area of activity is clinical genetics, which centres on advising parents of the likelihood of their children being affected by genetic disease caused by mutant genes and abnormal chromosome structure and umber. Such genetic counseling is based on examining individual and family medical records and on diagnosticprocedures that can detect unexpressed, abnormal forms of genes. Counseling is carried out by physicians with a particular interest in this area or by specially trained nonphysicians.
Genomics
Genomics is the study of the structure, function, and inheritance of the genome (entire set of genetic material) of an organism. A major part of genomics is determining the sequence of molecules that make up the genomic DNA content of an organism. Every organism contains a basic set of chromosomes, unique in number and size for every species, that includes the complete set of genes plus any DNA between them. While the term genome was not brought into use until 1920, the existence of genomes has been known since the late 19th century, when chromosomes were first observed as stained bodies visible under the microscope. The initial discovery of chromosomes was then followed in the 20th century by the mapping of genes on chromosomes based on the frequency of exchange of parts of chromosomes by a process called chromosomal crossing over, an event that occurs as a part of the normal process of recombination and the production of sex cells (gametes) during meiosis. The genes that could be mapped by chromosomal crossing over were mainly those for which mutant phenotypes (visible manifestations of an organism’s genetic composition)had been observed, only a small proportion of the total genes in the genome. The discipline of genomics arose when the technology became available to deduce the complete nucleotide sequence of genomes, sequences generally in the range of billions of nucleotide pairs.
Functional Genomics:
Analysis of genes at the functional level is one of the main uses of genomics, an area known generally as functional genomics. Determining the function of individual genescan be done in several ways. Classical, or forward, genetic methodology starts with a randomly obtained mutant ofinteresting phenotype and uses this to find the normal gene sequence and its function. Reverse genetics starts with the normal gene sequence (as obtained by genomics), induces a targeted mutation into the gene, then, by observing howthe mutation changes phenotype, deduces the normal function of the gene. The two approaches, forward and reverse, are complementary. Often a gene identified by forward genetics has been mapped to one specific chromosomal region, and the full genomic sequence reveals a gene in this position with an already annotated function.
Functional Genomics:
Analysis of genes at the functional level is one of the main uses of genomics, an area known generally as functional genomics. Determining the function of individual genescan be done in several ways. Classical, or forward, genetic methodology starts with a randomly obtained mutant ofinteresting phenotype and uses this to find the normal gene sequence and its function. Reverse genetics starts with the normal gene sequence (as obtained by genomics), induces a targeted mutation into the gene, then, by observing howthe mutation changes phenotype, deduces the normal function of the gene. The two approaches, forward and reverse, are complementary. Often a gene identified by forward genetics has been mapped to one specific chromosomal region, and the full genomic sequence reveals a gene in this position with an already annotated function.
Genetic engineering
Genetic engineering involves the altering of proteins within the genes in DNA. There are many types of manipulation, some leading to new discoveries and the identification of individual genes. Different plants and animals are frequently used as subjects in genetic research, and recent advances in human gene therapy studies may have implications for the future of health care.
Genetic engineering is essentially a practice in which the genes of an individual organism are altered by some measured control over the DNA.
Modern genetic engineering uses molecular cloning and transformation to manipulate the structure of the proteins in a gene. Those proteins can be restructured and resequenced for a desired outcome. Many applications, such as food modification and pure research, have grown from the studies
Genetic engineering on humans has become more commonplace over the years. Somatic modification targets a problem gene and allows scientists to inject healthy genes to alter the effects of the disorder.
Gene therapy studies began in 1990 with the initial focus on "bubble children," individuals who are susceptible to common bacteria found everywhere.
Genetic engineering is essentially a practice in which the genes of an individual organism are altered by some measured control over the DNA.
Modern genetic engineering uses molecular cloning and transformation to manipulate the structure of the proteins in a gene. Those proteins can be restructured and resequenced for a desired outcome. Many applications, such as food modification and pure research, have grown from the studies
Genetic engineering on humans has become more commonplace over the years. Somatic modification targets a problem gene and allows scientists to inject healthy genes to alter the effects of the disorder.
Gene therapy studies began in 1990 with the initial focus on "bubble children," individuals who are susceptible to common bacteria found everywhere.
A-DNA
A-DNA is also a right-handed helix. However, there are more base pairs per turn. A-DNA has 11 base pairs per turn. Other than the more compact structure, A-DNA is similar to B-DNA. It is biologically active in the cell, and it forms crystallized structures in lab experiments.
A-DNA is one of the many possible double helical structures of DNA. A-DNA is thought to be one of three biologically active double helical structures along with B- and Z-DNA. It is a right-handed double helix fairly similar to the more common and well-known B-DNA form, but with a shorter more compact helical structure.
It appears likely that it occurs only in dehydrated samples of DNA, such as those used in crystallographic experiments, and possibly is also assumed by DNA-RNA hybrid helices and by regions of double-stranded RNA.
A-DNA is one of the many possible double helical structures of DNA. A-DNA is thought to be one of three biologically active double helical structures along with B- and Z-DNA. It is a right-handed double helix fairly similar to the more common and well-known B-DNA form, but with a shorter more compact helical structure.
It appears likely that it occurs only in dehydrated samples of DNA, such as those used in crystallographic experiments, and possibly is also assumed by DNA-RNA hybrid helices and by regions of double-stranded RNA.
B-DNA
B-DNA is the form commonly observed in chromosomes. B-DNA is a right-handed helix with 10 base pairs per turn.
B-DNA is replicated and used in the transcription and translation of RNA, which is the molecule used for protein synthesis.
B-DNA can be denatured, which means the hydrogen bonds are removed. This is essentially the first step in replicating DNA in the cell
B-DNA is replicated and used in the transcription and translation of RNA, which is the molecule used for protein synthesis.
B-DNA can be denatured, which means the hydrogen bonds are removed. This is essentially the first step in replicating DNA in the cell
c DNA
cDNA (complementary or clonal DNA) is a type of DNA used to describe libraries of genetic information. cDNA is used in testing for pharmaceuticals and research of diseases. cDNA is a complementary strand that is transcribed in laboratories to create genes.
Genetic engineering also uses these DNA libraries to create modified versions of genomic information.
C-DNA also known as C form DNA. It is one of the many possible double helical structures of DNA.
This form of DNA could be observed at some conditions that relatively low humidity and with certain ions, such as Li+ or Mg2+.
Recent research suggests that both C-DNA and B-DNA consist of two distinct nucleotide conformations, B-I and B-II. The ratio of B-II conformation in C-DNA is more than 40%. However, the ratio of B-II conformation in B-DNA is only about 10%.
Genetic engineering also uses these DNA libraries to create modified versions of genomic information.
C-DNA also known as C form DNA. It is one of the many possible double helical structures of DNA.
This form of DNA could be observed at some conditions that relatively low humidity and with certain ions, such as Li+ or Mg2+.
Recent research suggests that both C-DNA and B-DNA consist of two distinct nucleotide conformations, B-I and B-II. The ratio of B-II conformation in C-DNA is more than 40%. However, the ratio of B-II conformation in B-DNA is only about 10%.
DNA Evidence
DNA evidence is widely called the "fingerprint of the 21st century" and has the unequaled ability to identify rapists and exonerate innocent suspects. But the use of DNA evidence has not kept pace with its potential.
In the last decade, DNA evidence from hundreds of thousands of rape and murder cases was collected by police but never sent to labs for analysis. As this evidence backlog -- one of the biggest impediments to getting rapists off the streets -- became overwhelming for states and localities, RAINN concluded that a federal solution was necessary.
To help launch the effort, RAINN led a successful national campaign to educate the media and lawmakers about the backlog of unanalyzed DNA casework and bring this enormous problem to public attention. RAINN's president and founder, Scott Berkowitz, also testified before the U.S. Congress regarding the DNA testing backlog.
In the last decade, DNA evidence from hundreds of thousands of rape and murder cases was collected by police but never sent to labs for analysis. As this evidence backlog -- one of the biggest impediments to getting rapists off the streets -- became overwhelming for states and localities, RAINN concluded that a federal solution was necessary.
To help launch the effort, RAINN led a successful national campaign to educate the media and lawmakers about the backlog of unanalyzed DNA casework and bring this enormous problem to public attention. RAINN's president and founder, Scott Berkowitz, also testified before the U.S. Congress regarding the DNA testing backlog.
DNA Sequencing
Over the past 10 years DNA sequencing has declined rapidly in cost. It's hoped that future advances will make it cheap enough that it can find more frequent use in medicine and medical research in sequencing the genomes of cancer cells, for example.
DNA has traditionally been sequenced using more advanced variations on a technique called chain termination or Sanger sequencing. Some researchers, however, are working on techniques that could eventually supplant chain termination methods and drive cost down further still.
DNA has traditionally been sequenced using more advanced variations on a technique called chain termination or Sanger sequencing. Some researchers, however, are working on techniques that could eventually supplant chain termination methods and drive cost down further still.
DNA Structure
DNA types are differentiated by their formation and helix structure. The components of the double helix are specific for all DNA.
DNA consists of a sugar-phosphate backbone with an internal nitrogenous base. The nitrogenous base's hydrogen bond holds the double helix structure by combining two complementary strands of DNA.
The external backbone is negatively charged, providing interaction with other molecules.
DNA consists of a sugar-phosphate backbone with an internal nitrogenous base. The nitrogenous base's hydrogen bond holds the double helix structure by combining two complementary strands of DNA.
The external backbone is negatively charged, providing interaction with other molecules.
miRNA
A microRNA (miRNA) is a short, non-coding RNA. miRNA molecules are complementary to parts of mRNA sequences and regulate gene expression by binding to mRNA to inhibit protein translation
miRNAs show very different characteristics between plants and metazoans. In plants the miRNA complementarity to its mRNA target is nearly perfect, with no or few mismatched bases. In metazoans on the other hand miRNA complementarity is far from perfect and one miRNA can target many different sites on the same mRNA or on many different mRNAs.
Another difference is the location of target sites on mRNAs. In metazoans the miRNA target sites are in the three prime untranslated regions (3'UTR) of the mRNA. In plants targets can be located in the 3' UTR but are more often in the coding region itself. MiRNAs are well conserved in eukaryotic organisms and are thought to be a vital and evolutionarily ancient component of genetic regulation.
miRNAs show very different characteristics between plants and metazoans. In plants the miRNA complementarity to its mRNA target is nearly perfect, with no or few mismatched bases. In metazoans on the other hand miRNA complementarity is far from perfect and one miRNA can target many different sites on the same mRNA or on many different mRNAs.
Another difference is the location of target sites on mRNAs. In metazoans the miRNA target sites are in the three prime untranslated regions (3'UTR) of the mRNA. In plants targets can be located in the 3' UTR but are more often in the coding region itself. MiRNAs are well conserved in eukaryotic organisms and are thought to be a vital and evolutionarily ancient component of genetic regulation.
m RNA
Messenger RNA (mRNA) carries information on how to construct a protein. It is transcribed from DNA and taken to ribosomes. Ribosomes "read" mRNA to link amino acids together in a specific sequence
Messenger RNA (mRNA) is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcribed from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes
Here, the nucleic acid polymer is translated into a polymer of amino acids: a protein. In mRNA as in DNA, genetic information is encoded in the sequence of nucleotides arranged into codons consisting of three bases each. Each codon encodes for a specific amino acid, except the stop codons that terminate protein synthesis.
Messenger RNA (mRNA) is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcribed from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes
Here, the nucleic acid polymer is translated into a polymer of amino acids: a protein. In mRNA as in DNA, genetic information is encoded in the sequence of nucleotides arranged into codons consisting of three bases each. Each codon encodes for a specific amino acid, except the stop codons that terminate protein synthesis.
Recombinant DNA
Recombinant DNA is created by incorporating DNA from two or more sources into a single molecule. First, both the original molecule and the sequence researchers want to insert are cut with restriction enzymes, proteins that make cuts at specific sequences in DNA.
Next an enzyme called ligase is used to seal the two together into a single molecule. Often, other genes besides the gene of interest will also be introduced in order to distinguish bacteria or cells that successfully take up the new DNA from those that do not.
The DNA can be introduced easily into bacteria using several different techniques; transfecting plant or animal cells with DNA is more difficult, although scientists have developed techniques to do this as well. Gene cloning is a procedure that involves making copies of a gene by inserting it into a circular piece of DNA then introducing this DNA into bacteria.
Another common recombinant DNA technique involves adding a reporter gene called GFP (green fluorescent protein) to a gene of interest and introducing this gene into a cell; since the GFP will make the protein product of the gene fluorescent, scientists can use this approach to track the protein product and its interactions. Genes can also be "knocked out" by altering the gene in a way that will disable it in the cell
Next an enzyme called ligase is used to seal the two together into a single molecule. Often, other genes besides the gene of interest will also be introduced in order to distinguish bacteria or cells that successfully take up the new DNA from those that do not.
The DNA can be introduced easily into bacteria using several different techniques; transfecting plant or animal cells with DNA is more difficult, although scientists have developed techniques to do this as well. Gene cloning is a procedure that involves making copies of a gene by inserting it into a circular piece of DNA then introducing this DNA into bacteria.
Another common recombinant DNA technique involves adding a reporter gene called GFP (green fluorescent protein) to a gene of interest and introducing this gene into a cell; since the GFP will make the protein product of the gene fluorescent, scientists can use this approach to track the protein product and its interactions. Genes can also be "knocked out" by altering the gene in a way that will disable it in the cell
Gene Therapy
Gene therapy is the insertion, alteration, or removal of genes within an individual's cells and biological tissues to treat disease. It is a technique for correcting defective genes that are responsible for disease development.
The most common form of gene therapy involves the insertion of functional genes into an unspecified genomic location in order to replace a mutated gene, but other forms involve directly correcting the mutation or modifying normal gene that enables a viral infection.
Although the technology is still in its infancy, it has been used with some success.
The most common form of gene therapy involves the insertion of functional genes into an unspecified genomic location in order to replace a mutated gene, but other forms involve directly correcting the mutation or modifying normal gene that enables a viral infection.
Although the technology is still in its infancy, it has been used with some success.
r RNA
Ribosomal ribonucleic acid (rRNA) is the RNA component of the ribosome, the organelle that is the site of protein synthesis in all living cells. Ribosomal RNA provides a mechanism for decoding mRNA into amino acids and interacts with tRNAs during translation by providing peptidyl transferase activity.
The tRNAs bring the necessary amino acids corresponding to the appropriate mRNA codon.
Ribosomal RNA (rRNA) is also transcribed from DNA but is not a code carrier. This RNA becomes a structural part of the protein synthesizing molecular machines known as ribosomes.
The tRNAs bring the necessary amino acids corresponding to the appropriate mRNA codon.
Ribosomal RNA (rRNA) is also transcribed from DNA but is not a code carrier. This RNA becomes a structural part of the protein synthesizing molecular machines known as ribosomes.
t RNA
Transfer RNA (tRNA) has a coding section and an amino acid carrying section. The code identifies which amino acid is carried so that the proper amino acids are used at ribosomes during protein synthesis.
Each type of tRNA molecule can be attached to only one type of amino acid, but because the genetic code contains multiple codons that specify the same amino acid, tRNA molecules bearing different anticodons may also carry the same amino acid.
Each type of tRNA molecule can be attached to only one type of amino acid, but because the genetic code contains multiple codons that specify the same amino acid, tRNA molecules bearing different anticodons may also carry the same amino acid.
Z-DNA
Z-DNA is the type of DNA that is a left-handed helix. It is also known to be biologically active in zigzag formations of repeating base pair sequences. Z-DNA has 12 base pairs per turn, so it carries the most genes between each turn. Z-DNA plays a role in RNA transcription, which is the protein synthesis process of creating mRNA from a strand of DNA. mRNA (message RNA) is the molecule that carries transcribed genes to ribosomes where proteins are synthesized.
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