Genetics in Medicine - Part 3
Legal Issues - Ownership Of Tissues, Criminal Law, Patenting Issues
The question of who owns tissues, DNA, and other biological materials raises numerous legal questions. One concern is that genetic information derived from someone's DNA sequences could be used to deny insurance coverage to people whose genes indicate that they have a disease or that they are at risk of contracting one. Another concern is that the profits made by hospitals and transplant ce…
Mapping - Why Create And Use Maps?, Using Recombination And Map Functions, Types Of Markers, And Their Advantages And Disadvantages
Genetic mapping is the process of measuring the distance between two or more loci on a chromosome. In order to determine this distance, a number of things must be done. First, the loci (pronounced "low-sigh") have to be known, and alleles have to exist at each locus so that they can be observed. The specific pair of alleles that are present is usually referred to as a geno-type. Seco…
Marker Systems - Selectable Markers, Screenable Markers
Marker systems are tools for studying the transfer of genes into an experimental organism. In gene transfer studies, a foreign gene, called a trans-gene, is placed into an organism, in a process called transformation. A common problem for researchers is to determine quickly and easily if the target cells of the organism have actually taken up the transgene. A marker allows the researcher to determ…
Mass Spectrometry - Accelerate Ionize Detect, Applications
Mass spectrometry is a technique for separating and identifying molecules based on mass. It has become an important tool for proteomics, the analysis of the whole range of proteins expressed in a cell. Mass spectrometry is used to identify proteins and to determine their amino acid sequence. It can also be used to determine if a protein has been modified by the addition of phosphate groups or suga…
Barbara McClintock
Barbara McClintock, having just received the prestigious $15,000 Lasker Award in 1981 for her many contributions to the field of genetics. Geneticist 1902-1992 Barbara McClintock was one of the most important geneticists of the twentieth century and among the most controversial women in the history of science. She made several fundamental contributions to our understanding of chromosome str…
Victor McKusick
Geneticist 1921- Victor Almon McKusick was born in the little town of Parkman in central Maine, on October 21, 1921. He went to Tufts College in Boston from Victor McKusick 1940 to 1943, and then received his medical degree from Johns Hopkins University in 1946. He has remained at Johns Hopkins ever since, rising from a medical student to physician-in-chief of the entire Johns Hopkins hospit…
Mendelian Genetics - The Principle Of Segregation, The Principle Of Independent Assortment, Exceptions To Mendel's Laws
Gregor Mendel (1822-1884), an Austrian monk and botanist, was curious and loved nature. He grew plants with diverse flower colors, and he cross-pollinated plant varieties to create hybrids. Mendel's fascination with "the striking regularity with which the same hybrid forms always reappeared," broadened his quest into discovering laws for inheriting any trait, not just flower c…
Metabolic Disease - Enzymes Control Metabolic Reactions, Enzyme Defects Cause Metabolic Disorders, Approaches To Treatment, Major Classes Of Metabolic Disorders - Disorders of Amino Acid Metabolism, Disorders of Organic Acid Metabolism, Disorders of Fatty
Metabolism is the sum of the chemical processes and interconversions that take place in the cells and the fluids of the body. This includes the absorption of nutrients and minerals, the breakdown and buildup of large molecules, the interconversion of small molecules, and the production of energy from these chemical reactions. Virtually every chemical step of metabolism is catalyzed by an enzyme. D…
Microbiologist
A microbiologist studies living organisms that are invisible to the naked eye. Microbiologists study bacteria, fungi, and other one-celled organisms (microbes), as well as viruses. A microbiologist may study a single molecule isolated from a bacterium, or a complex ecosystem with many microbial species. In the course of their work, microbiologists do a variety of tasks. These include inoculating m…
Mitochondrial Diseases - The Importance Of The Electron Transport Chain, Mitochondrial Genes And Disease
Mitochondria are intracellular organelles that play a critical role in cellular metabolism. Mitochondria contain the electron transport chain, which transfers electrons to oxygen by means of a process called oxidative phosphorylation. This process releases energy for the production of adenosine triphosphate (ATP) by forming a pH and electrical gradient (called the chemiosmotic gradient) across the…
Mitosis - Differences between Mitosis and Meiosis
Mitosis is the process by which all cells divide. Many cells have a limited life span, and mitosis allows them to be renewed on a regular basis. Mitosis is also responsible for generating the many millions of cells that are needed for an embryo to develop into a fetus, an infant, and finally an adult. Most human cells continually undergo a cycle of different phases. The phases have distinct names …
Model Organisms - Useful Traits And Attributes, The Model Mouse
A model organism is a species that biologists choose to study, not necessarily because it has any inherent medical, agricultural, or economic value, but because it has certain traits that make it easy and convenient to work with. Studying model organisms enables researchers to perform experiments that might be impossible to carry out, due to logistical, financial, or ethical constraints, on organi…
Mosaicism - The Sex Chromosomes, Mosaic Expression, X Chromosome Inactivation, Effect Of X Inactivation On Human Disease
In 1961 Mary Lyon, an English scientist, hypothesized that one of the two X chromosomes in females becomes genetically silent early in a female embryo's development. To understand how she arrived at this idea, which has come to be known as "the Lyon Hypothesis," we need to understand what was known about the sex chromosomes. Every time a cell divides, the genetic material asse…
Hermann Muller
Hermann Muller. Geneticist 1890-1967 Hermann Joseph Muller was one of the founding members of the "fly lab" that was initiated by Thomas Hunt Morgan. In the early part of the twentieth century, this lab was the center of important research into the role of chromosomes in inheritance, using the fruit fly Drosophila as a model organism in experiments. The major members included …
Mutagenesis - Noninduced Mutagenic Agents, Creating Mutations, The First Mutagenesis Assay, Detecting Mutations
Mutagenesis is the process of inducing mutations. Mutations may occur due to exposure to natural mutagens such as ultraviolet (UV) light, to industrial or environmental mutagens such as benzene or asbestos, or by deliberate mutagenesis for purposes of genetic research. For geneticists, the study of mutagenesis is important because mutants reveal the genetic mechanisms underlying heredity and gene …
Mutation - Phenotypic Effects And Evolution, Molecular Basis Of Mutations, Point Mutations, Chromosomal Aberrations And Transposons
A mutation is any heritable change in the genome of an organism. For a population, heritable mutations provide the source of genetic variation, without which evolution could not occur: If all individuals of a species were genetically identical, every subsequent generation would be identical regardless of which members of the species reproduced successfully. For an individual organism, mutations ar…
Nomenclature
Like any other field in science, genetics has its own language. However, genetics is also a multidisciplinary field that encompasses expertise, and hence terminology, from diverse areas of science, including molecular biology, statistics, clinical medicine, and, most recently, bioinformatics. Despite all of the new and changing language in the field, two of the most frequently used terms in geneti…
Nucleases - The Nuclease Mechanism, Deoxyribonucleases In Dna Replication And Repair, Ribonucleases In Rna Maturation And Degradation
DNA and RNA are polymers made by linking together smaller units called nucleotides. Nucleases are enzymes that break the chemical bonds, called phosphodiester bonds, that hold the nucleotides of DNA or RNA polymers together. Enzymes that cleave the phosphodiester bonds of DNA are called deoxyribonucleases, and enzymes that cleave the phosphodiester bonds of RNA are called ribonucleases. Nucleases …
Nucleus - Distinctive Features, Chromosomal Territories, Interchromatin Compartment, Nucleolus, Subnuclear Bodies, Nuclear Envelope, Nuclear Pores
The largest of the membrane-bound organelles, the nucleus first was described in 1710 by Antoni van Leeuwenhoek using a simple microscope. In 1831 the Scottish botanist Robert Brown characterized the organelle in detail, calling it the "nucleus," from the Latin word for "little nut." The nucleus is the site of gene expression and gene regulation. By electron microscopy,…
Overlapping Genes
Overlapping genes are defined as a pair of adjacent genes whose coding regions are partially overlapping. In other words, a single stretch of DNA codes for portions of two separate proteins. Such an arrangement of genetic code is ubiquitous. Many overlapping genes have been identified in the genomes of prokaryotes, eukaryotes, mitochondria, and viruses. For two genes to overlap, the signal to begi…
Patenting Genes - Patent Requirements, The Patent Process
A patent is a legal right granted by the government that gives the patent-holder the exclusive right to manufacture and profit from an invention. While naturally occurring substances in their natural form are not patentable, a very wide range of biological materials have been the subject of patents. In 1980 the U.S. Supreme Court decision in Diamond v. Chakrabarty indicated that "anything u…
Pharmaceutical Scientist
The role of the pharmaceutical scientist in drug discovery and development is highly varied. Duties range from the synthesis of novel compounds designed to alter disease processes, to the formulation of these compounds into a tablet or capsule, to the development of assays (tests) to measure the drug and its metabolites in the body, to the testing of compounds for their effects in animals and huma…
Physician Scientist
According to Webster's II New College Dictionary, a physician is "a natural philosopher, a person skilled in physic, or the art of healing; one duly authorized to prescribe remedies for, and treat, diseases; a doctor of medicine." A scientist is one who is "learned in the observation, identification, description, experimental investigation, and theoretical explanation o…
Plant Genetic Engineer
"Plant genetic engineer" is a popular term that describes scientists working in any of several fields who manipulate DNA or organelles such as chloroplasts and mitochondria in plant cells. The specific titles of such a scientist can include plant physiologist, plant pathologist, weed scientist, cell biologist, botanist, molecular biologist, plant geneticist, and biochemist. The typic…
Pleiotropy - Signaling Pathways
Pleiotropy is the phenomenon whereby a single gene has multiple consequences in numerous tissues. Pleiotropic effects stem from both normal and mutated genes, but those caused by mutations are often more noticeable and easier to study. Pleiotropy is actually more common than its opposite, since in a complex organism, a protein from a single gene is likely to be expressed in more than one tissue, a…
Polymerase Chain Reaction - Designing Primers, A Typical Pcr Reaction, Contamination In Pcr Reactions, Pcr Applications And Variations
The polymerase chain reaction (PCR) is a laboratory technique for "amplifying" a specific DNA sequence. PCR is extremely efficient and sensitive; it can make millions or billions of copies of any specific sequence of DNA, even when the sequence is in a complex mixture. Because of this power, researchers can use it to amplify sequences even if they only have a minute amount of DNA. A …
Polyploidy - Polyploidy In Animals, Polyploidy In Plants, Genetic Analysis
In eukaryotic organisms, chromosomes come in sets. The somatic cells, called soma, usually have a diploid chromosome number, which in scientific notation is abbreviated as 2N. The diploid state contains two sets of chromosomes, one set of which has been contributed by each parent. A single set of chromosomes composes the haploid chromosome number, which is abbreviated as N. The haploid set is foun…
Population Bottleneck - Reconstructing Genealogies, Reconstructing Ancient Population Sizes, Technological And Social Influences On Past Population Size - Population Bottlenecks and Expansions in Human Evolution
A population bottleneck is a significant reduction in the size of a population that causes the extinction of many genetic lineages within that population, thus decreasing genetic diversity. Population bottlenecks have occurred in the evolutionary history of many species, including humans. Present-day bottlenecks are seen in endangered species such as the Yangtze River dolphin, whose numbers have d…
Population Screening - Screening Versus Diagnostic Tests, Criteria For A Screening Program, Screening For Inherited Disorders, Ethical Considerations
As scientific research reveals more information about treating diseases and maintaining good health, it has become increasingly important to identify diseases in their early stages in order to treat them most effectively. Thus, researchers have developed tests for some diseases to identify people at high risk for the disease before the symptoms of the disease actually appear. These tests are routi…
Prenatal Diagnosis - Viewing Chromosomes, Less Invasive Methods, Preimplantation Genetic Diagnosis, Genetic Counseling And The Ethics Of Prenatal Diagnosis
The future health of a new individual can be predicted, to an extent, from clues that are apparent before birth. Prenatal diagnosis is the identification of a medical condition in a developing embryo or fetus. Prenatal testing can sample fetal cells to examine DNA sequences that correspond to specific disease-causing genes or chromosomes (the structures that carry the genes). Biochemicals obtained…
Proteins - Properties Of Amino Acids, Primary Structure, Secondary Structure And Motifs, Tertiary Structure And Protein Domains - Molecular Chaperones, Proteomics
Proteins are polymers of amino acids that provide structure and control reactions in all cells. When humans think of expressing the meaning of life, they often resort to words. From poems to sonnets to short stories to novels, words tell the stories of life. But in biological terms, the words of life are proteins. While DNA holds the code of life, proteins are the language in which that code is ex…
Proteomics - Laboratory Techniques, Databases And Computational Approaches
Proteomics is the science of studying the multitude of proteomes found in living organisms. A proteome is the entire collection of proteins expressed by a genome or in a tissue. The contents of a proteome can differ in various tissue types, and it can change as a result of aging, disease, drug treatment, or environmental effects. This is contrary to the concept of a genome, which is an organism&#x…
Pseudogenes - Nonprocessed Pseudogenes, Processed Pseudogenes, Pseudogene Examples
Pseudogenes are defective copies of functional genes. These may be partial or complete duplicates derived from polypeptide-encoding genes or RNA genes. The DNA sequence of a pseudogene is characteristically very similar to its functional counterpart, but contains variant mutations that render the gene inactive. The functional polypeptide-encoding gene contains an open reading frame, a long stretch…
Genetic Techniques in Public Health - Public Health Approaches In Genetics, Applied Research, Evaluation Of Genetic Information And Tests, Development, Implementation, And Evaluation Of Population Interventions
As of 2002 more than ten thousand genes have been discovered, and it is estimated that 30,000 to 70,000 human genes will be identified as a result of the Human Genome Project over the following few years. Tests for more than 600 gene variants are already available in medical practice. Genetic variants, or polymorphisms, are a normal part of genetic viability that may or may not be associated with …
Purification of DNA
Many procedures in molecular biology require an initial pure sample of DNA. These procedures include the polymerase chain reaction, sequencing, gene cloning, blotting, and DNA profiling. Purification of DNA involves removing it and other constituents from the cell, separating it from the various other cell constituents, and protecting it from degradation by cellular enzymes. Isolation procedures m…