Human progeria comes in two major forms, Werner's syndrome (adult-onset progeria) and Hutchinson-Gilford syndrome (juvenile-onset progeria). Werner's patients are usually diagnosed in early maturity and have an average life span of forty-seven years. Hutchinson-Gilford patients are usually diagnosed within the first two years of life and have an average life span of thirteen years. T…
Addiction in its broadest sense can be defined as the habituation to a practice considered harmful. A more narrow definition of the term refers to chronic use of a chemical substance in spite of severe psychosocial consequences. Terms such as "workaholic," "sex addict," and "computer junkie" arose to describe behaviors that have features in common with alc…
Aging is, simply put, the act of getting older. Aging is part of the natural life cycle of an organism. From birth, through maturation, and eventually to death, aging is the element that ties all segments of life together. …
Biotechnology is the use of living organisms—microbes, plants, or animals—to provide useful new products or processes. In a broad sense, biotechnology continues a process that is thousands of years old. Using traditional plant breeding techniques, humans have altered the genetic composition of almost every crop by only planting seeds from plants with desired traits, or by controlling…
When molecular biologists began analyzing the complete sequence of the human genome in mid-2001, one surprising observation was that humans have relatively few genes. We may have as few as 30,000 genes, only about two Introns are removed by the spliceosomes. times as many as the much simpler fruit fly, Drosophila melanogaster. How can the much greater size and complexity of humans be encoded…
Alzheimer's disease (AD) is a diagnosis applied to a group of degenerative brain disorders with similar clinical and pathological characteristics. It is the most common cause of dementia, with onset of symptoms after the age of fifty-five years. It is recognized as a major public health concern in societies with an aging population. AD affects four million people in the United States. At le…
O6-ethylguanine. The Ames test is a protocol for identifying mutagenic chemical and physical agents. Mutagens generate changes in DNA. Many mutagenic agents modify the chemical structure of adenine, thymine, guanine, and cytosine, the bases in DNA, changing their base-pairing properties and causing mutations to accumulate during DNA synthesis. Ethyl methanesulfonate (EMS), for example, is a…
Androgen insensitivity syndrome (AIS) is a disorder caused by mutation of the gene for the androgen receptor. This protein binds testosterone and regulates the expression of other genes that stimulate male sexual development. Testosterone is the principal male androgen. AIS is an X-linked recessive disorder that completely or partially prevents development of male sexual characteristics despite th…
Antibiotic resistance is the ability of a bacterium or other microorganism to survive and reproduce in the presence of antibiotic doses that were previously thought effective against them. Examples of microbe resistance to antibiotics dot the countryside, plaguing humankind. For instance, in February 1994 dozens of students at La Quinta High School in southern California were exposed to the pathog…
Antisense nucleotides are strings of RNA or DNA that are complementary to "sense" strands of nucleotides. They bind to and inactivate these sense strands. They have been used in research, and may become useful for therapy of certain diseases. …
Death is an inevitable fact of life for organisms. Increasingly, biologists have come to realize that death is also, in many cases, an important and predestined fate of individual cells of organisms. Apoptosis is a process by which cells in a multicellular organism commit suicide. While cells can die as a result of necrosis, apoptosis is a form of death that the cell itself initiates, regulates, a…
Arabidopsis thaliana, or thale cress, is a small flowering plant in the mustard family. Arabidopsis has no inherent agricultural value and is even considered a weed, but it is one of the favored model organisms of plant geneticists and molecular biologists, and it is the most thoroughly studied plant species at the molecular level. Model organisms have traits that make them attractive and convenie…
Members of the Archaea comprise one of the three principal domains of living organisms in the universal phylogenetic tree of life. The other two principal domains are the Bacteria and the Eukarya. The phylogenetic tree is a theoretical representation of all living things, constructed on the basis of comparative ribosomal RNA sequencing and reflecting evolutionary relationships rather than structur…
Attention deficit/hyperactivity disorder (ADHD) is a condition characterized by inattention and/or impulsivity and hyperactivity that begins in children prior to the age of seven. Their inattention leads to daydreaming, distractibility, and difficulties sustaining effort on a single task for a prolonged period of time. Their impulsivity disrupts classrooms and creates problems with peers, as they …
Attorneys involved with genetics include criminal prosecutors (district attorneys), public defenders, environmental lawyers, family lawyers, and patent attorneys. Genetics is relevant in the areas of identification of suspects and victims, identification of illegal goods (for example, items that involve the killing of endangered animals), environmental monitoring for harmful microorganisms, parent…
The process of determining the order of nucleotides (A, C, G, and T) along a DNA strand is called DNA sequencing. Knowing the nucleotide sequence of a gene or region of DNA is important in studying relatedness between species and between individuals and for a better understanding of how genes function. Several techniques have been developed for "reading" the sequence of any particula…
Balanced polymorphism is a situation in which two different versions of a gene are maintained in a population of organisms because individuals carrying both versions are better able to survive than those who have two copies of either version alone. The evolutionary process that maintains the two versions over time is called balancing selection. Genes are carried on chromosomes. Different versions …
What is behavior? A dictionary definition reveals that behavior consists of our activities and actions, especially actions toward one another. As such definitions suggest, many behavioral terms have meaning only in social comparisons: We identify others as contentious, courteous, or conscientious only by their actions in social contexts. A long-standing question in science and in everyday affairs …
Bioinformatics is the use of mathematical, statistical and computer methods to analyze biological, biochemical, and biophysical data. Because bioinformatics is a young, rapidly evolving field, however, it also has a number of other credible definitions. It can also be defined as the science and technology of learning, managing, and processing biological information. Bioinformatics is often focused…
Plants, growing in the wild or in cultivation, face numerous threats from insects, bacteria, viruses, and fungi, as well as from other plants. Biopesticides are inert substances or living organisms that can help protect plants from such threats. Chemical pesticides can offer similar protection but, by contrast, are neither alive nor made by living organisms. A variety of chemicals produced by plan…
Bioremediation is the use of organisms to break down and thereby detoxify dangerous chemicals in the environment. Plants and microorganisms are used as bioremediators. The technology can take advantage of a natural metabolic pathway or genetically modify an organism to have a particular toxic "appetite." …
Biotechnology, broadly defined, refers to the manipulation of biology or a biological product for some human end. Before recorded history, humans grew selected plants for food and medicines. They bred animals for food, for work, and as pets. The ancient Egyptians learned how to maintain selected yeast cultures, which allowed them to bake and brew with predictable results. These are all examples of…
The biotechnology entrepreneur often starts with a technical background, most commonly including scientific laboratory research. It is quite common for scientists who have spent a number of years in an academic environment to start a new company based on a technology platform or a novel discovery they made during their tenure at a university or research institute. Alternatively, a scientist or a g…
Biotechnology is the use of organisms or their parts or products to provide a valuable substance or process. Fermentation using microorganisms in brewing, baking, and cheese production are biotechnologies that date back centuries. Production of human insulin in bacteria to treat type I diabetes mellitus without causing allergic reactions is a more modern example of biotechnology. Two widely used b…
The term "biotechnology" dates from 1919, when the Hungarian engineer Karl Ereky first used it to mean "any product produced from raw materials with the aid of living organisms." Using the term in its broadest sense, biotechnology can be traced to prehistoric times, when huntergatherers began to settle down, plant crops, and breed animals for food. Ancient civilizations…
A birth defect is an anomaly that is congenital, or present from birth. Birth defects are the leading cause of infant mortality, causing 22 percent of all infant deaths. Approximately 3 to 4 percent of all live births are affected by a birth defect; the causes of most of them are unknown. Some birth defects are considered to be physical, while others are thought of as functional. Physical birth de…
Blood has two main components: serum and cells. In 1900 Karl Landsteiner, a physician at the University of Vienna, Austria, noted that the sera of some individuals caused the red cells of others to agglutinate. This observation led to the discovery of the ABO blood group system, for which Landsteiner received the Nobel Prize. Based on the reactions between the red blood cells and the sera, he was …
Blotting is a common laboratory procedure in which biological molecules in a gel matrix are transferred onto nitrocellulose paper for further scientific analysis. The biological molecules transferred in this process are DNA fragments, RNA fragments, or proteins. Because the isolation and characterization of these types of materials is at the center of much molecular biology research, blotting is o…
Breast cancer remains the most common cause of cancer among women in the United States, and it results in more deaths from cancer among women than any other type of cancer, except lung cancer. Over 40,000 women die from breast cancer in the United States each year. A long history of research, now coupled with the new information emerging from the field of molecular genetics, is beginning to explai…
Cancer is a number of related diseases that are characterized by the uncontrolled proliferation and disorganized growth of cells. Tumor cells invade and destroy normal tissues and may spread throughout the body via the circulatory systems. The body consists of many different organs, which in turn are composed of several different types of tissues. There are three major categories of tissue-related…
Carcinogens are agents that cause cancer, and include chemicals, radiation, and some viruses. While avoiding contact with carcinogenic agents is wise, it is virtually impossible to steer clear of them completely. Ultra-violet radiation from the sun, substances in food, and even oxygen can induce malignancies. In spite of the pervasive nature of carcinogens, however, not all individuals develop can…
Cardiovascular disease is a set of diseases affecting the heart and blood vessels. As with most chronic diseases whose incidence increases with age, it involves both inherited and environmental contributors and is therefore classified as a complex genetic disease. Most researchers believe that all major risk factors for cardiovascular disease have been identified. It is estimated that cigarette sm…
The cell cycle is the process by which a cell grows, duplicates its DNA, and divides into identical daughter cells. Cell cycle duration varies according to cell type and organism. In mammals, cell division occurs over a period of approximately twenty-four hours. In multicellular organisms, only a subset of cells go through the cycle continuously. Those cells include the stem cells of the hematopoi…
All living organisms are composed of cells. A eukaryotic cell is a cell with a nucleus, which contains the cell's chromosomes. Plants, animals, protists, and fungi have eukaryotic cells, unlike the Eubacteria and Archaea, whose cells do not have nuclei and are therefore termed prokaryotic. In addition to having a nucleus, eukaryotic cells differ from prokaryotic cells in being larger and mu…
During mitosis in a typical plant or animal cell, each chromosome divides longitudinally into two sister chromosomes that eventually separate and travel to opposite poles of the mitotic spindle. At the beginning of mitosis, when the sister chromosomes have split but are still paired, every chromosome attaches to the spindle at a specific point along its length. That point is referred to as the cen…
Molecular chaperones are proteins and protein complexes that bind to misfolded or unfolded polypeptide chains and affect the subsequent folding processes of these chains. All proteins are created at the ribosome as straight chains of amino acids, but must be folded into a precise, three-dimensional shape (conformation) in order to perform their specific functions. The misfolded or unfolded polypep…
Chromosomal aberrations are abnormalities in the structure or number of chromosomes and are often responsible for genetic disorders. For more than a century, scientists have been fascinated by the study of human chromosomes. It was not until 1956, however, that it was determined that the actual diploid number of chromosomes in a human cell was forty-six (22 pairs of autosomes and two sex chromosom…
A chromosome banding pattern is comprised of alternating light and dark stripes, or bands, that appear along its length after being stained with a dye. A unique banding pattern is used to identify each chromosome and to diagnose chromosomal aberrations, including chromosome breakage, loss, duplication or inverted segments. In the 1950s, chromosomes from the cell's nucleus were identified wi…
The chromosomal theory of inheritance is the idea that genes, the units of heredity, are physical in nature and are found in the chromosomes. The theory arose at the turn of the twentieth century, and became one of the cornerstones of the modern understanding of genetics. …
Living organisms are divided into two broad categories based upon certain attributes of cell structure. The first category, the prokaryotes, includes bacteria and blue-green algae. Eukaryotes include most other living organisms. One of the most important features distinguishing eukaryotes from prokaryotes is the chromosomal arrangement of genetic information in the cells. Eukaryotes enclose their …
The bacterial or prokaryotic chromosome differs in many ways from that of the eukaryote. The term "eukaryote" comes from the Greek and means "true nucleus." Eukaryotic cells have a double membrane (the nuclear membrane) surrounding the nucleus, the organelle that contains several chromosomes. In contrast, the term "prokaryote" means "primitive nucle…
Artificial chromosomes are laboratory constructs that contain DNA sequences and that perform the critical functions of natural chromosomes. They are used to introduce and control new DNA in a cell, to study how chromosomes function, and to map genes in genomes. …
Common garden peas (Pisum sativum) are wonderful when eaten raw. Gregor Mendel (1822-1884) no doubt ate his share. Today he is recognized for using peas to establish the science of genetics. Mendel investigated hereditary patterns of hybrids. Hybrids are off-spring from two organisms that are of different breeds, varieties, or species. Hybrids create new cultivars, from new apple varieties to tang…
Medical genetics is the application of genetics to the study of human health and diseases. As a profession, medical genetics is usually a mixture of both clinical services and research. Worldwide, services can include diagnosis, counseling, and management of birth defects and genetic disorders. How medical genetics is actually practiced depends on several factors, including the expertise and train…
Gene cloning, or molecular cloning, has several different meanings to a molecular biologist. A clone is an exact copy, or replica, of something. In the literal sense, cloning a gene means to make many exact copies of a segment of a DNA molecule that encodes a gene. This is in marked contrast to cloning an entire organism—regenerating a genetically identical copy of the organism—which…
Cloning is the creation of an individual that is a genetic replica of another individual. The process transfers a nucleus from a somatic nonreproductive cell into an "enucleated" fertilized egg, one that has had its own nucleus destroyed or removed. The genes in the transferred nucleus then direct the development of a complete organism from the altered fertilized egg. Two individuals…
There are two distinct types of cloning: molecular and organismal. Molecular cloning is the removal of a stretch of DNA, usually a gene, from an organism, and its insertion into another piece of DNA, such as a plasmid, to form a substance called recombinant DNA. This recombinant DNA may then be expressed in, or simply carried passively by, another organism, such as bacteria. Organismal cloning, th…
Professors of genetics at colleges and universities teach, perform research, and handle administrative responsibilities. Professors may teach at the undergraduate or graduate levels, or both. Undergraduate teaching involves class lectures, small group seminars, and hands-on laboratory sessions. Professors evaluate students based on their performances on examinations, essays, and laboratory work, a…
Colon cancer is the second leading cause of cancer death in the United States, occurring in approximately 5 percent of the population and resulting in roughly 55,000 deaths annually. New cases of colorectal cancer are diagnosed in approximately 90 per 100,000 people annually. The majority of cases occur in individuals older than age fifty. Of those who suffer from colorectal malignancy, an estimat…
Sight is a complex process that results when visible light, a narrow band of the electromagnetic spectrum between 400 and 700 nanometers (nm), is converted into signals that can be interpreted by the brain. This process involves special light-sensitive cells called photoreceptors that are located in the retina, a thin structure that lines the inside of the eye. These cells capture packets of light…
Combinatorial chemistry is a technology for creating a multitude of different compounds by reacting different combinations of interchangeable chemical "building blocks." The compounds are then screened for their ability to carry out a specified function, most commonly to act as drugs to treat a disease. Combinatorial chemistry allows the rapid synthesis and testing of many related co…
Complex traits are those that are influenced by more than one factor. The factors can be genetic or environmental. This is in contrast to simple genetic traits, whose variations are controlled by variations in single genes. Examples of simple traits include Huntington's disease and cystic fibrosis. Each of these traits is caused by a mutation in a single gene that alters or destroys the fun…
A computational biologist is a scientist who develops and utilizes computational tools to analyze biological data. The Human Genome Project and other large sequencing projects have generated an extraordinary amount of data. Biologists are now faced with the challenge of extracting meaning from linear sequences composed of billions of base pairs. The work of computational biologists is indispensabl…
Conjugation is one of several mechanisms that bacteria use to transfer DNA, and hence new genetic information, between two cells. The other primary mechanisms are transformation, in which free DNA is transported across the cell membrane, and transduction, in which DNA is carried into the recipient cell by a bacterial virus. …
Conservation biology is a multidisciplinary field dedicated to protecting global biodiversity and critical habitats. It incorporates biological approaches such as ecology, evolution, and behavior studies, as well as other disciplines, such as political science, law, economics, and cultural anthropology. One of the major goals of conservation biology is preserving critical habitats and the species …
A career path in conservation biology can be taken in many different directions, many of which are not centered around genetics. In general, the science of conservation biology draws upon many traditional academic disciplines, combining them in a science dedicated to maintaining Earth's biodiversity. In recent years, however, genetics has taken on an increasingly important role in the field…
British Biophysicist 1916- Francis Crick is the co-discoverer, with James Watson, of the structure of DNA. He has remained a significant contributor to theoretical biology since that discovery. …
Crossing over, or recombination, is the exchange of chromosome segments between nonsister chromatids in meiosis. Crossing over creates new combinations of genes in the gametes that are not found in either parent, contributing to genetic diversity. …
DNA sequencing is the process of determining the order of nucleotides on a segment of DNA. Cycle sequencing is a method used to increase the sensitivity of the DNA sequencing process and permits the use of very small amounts of DNA starting material. This is accomplished by using a temperature cycling process similar to that employed in the polymerase chain reaction. …
Cystic fibrosis (CF) is one of the most common genetic diseases and one of the best known to the general public. There are approximately one thousand new cases of CF in the United States every year, and approximately thirty thousand people in the country are currently affected. In many ways, it has come to be viewed, along with sickle-cell disease, as a prototypical recessive genetic disorder, one…
Physicist, Molecular Biologist 1906-1981 Max Delbrück made major contributions to the understanding of replication and viral function. Raised in Berlin in a distinguished family of German intellectuals, Delbrück trained as a physicist with Niels Bohr and other leaders in the field of quantum mechanics. In the early 1930s his interests turned toward biology and the nature of the gene. Thi…
Development is the process through which a multicellular organism arises from a single cell. During development, cells become specialized, or differentiated, taking on different functions and forms. The organism develops a characteristic three-dimensional shape, the parts of which (such as limbs and organs) continue to maintain the same relationship to each other even as the organism grows. How th…
Diabetes mellitus is a group of diseases characterized by elevated levels of glucose in the blood. Diabetes is caused by problems producing or responding to the hormone insulin. Insulin is produced in the pancreas by specialized cells called beta cells, in response to the presence of glucose absorbed through the gastrointestinal tract following a meal. Insulin promotes the uptake of glucose into m…
Genetics is believed to play a role in almost every human disease. Even for diseases traditionally described as environmental, such as tuberculosis and HIV, scientists are discovering that genetics is implicated either in the susceptibility to infection or in the severity of the disease. In some disorders a variation within a single gene is sufficient to cause disease, while in other disorders var…
DNA (deoxyribonucleic acid) was discovered in the late 1800s, but its role as the material of heredity was not elucidated for fifty years after that. It occupies a central and critical role in the cell as the genetic information in which all the information required to duplicate and maintain the organism. All information necessary to maintain and propagate life is contained within a linear array o…
DNA footprinting is a technique for identifying exactly where a protein binds to DNA. Knowing where a protein binds to DNA often aids in understanding how gene expression is regulated. Consequently, DNA footprinting is often part of a larger study to determine how a particular gene is controlled. …
DNA libraries, like conventional libraries, are used to collect and store information. In DNA libraries, the information is stored as a set of DNA molecules, each of which contains biological sequences that can be used for a variety of applications. All DNA libraries are collections of DNA fragments that represent a particular biological system of interest. By analyzing the DNA from a particular o…
DNA microarrays are tools used to analyze and measure the activity of genes. Researchers can use microarrays and other methods to measure changes in gene expression and thereby learn how cells respond to a disease or to some other challenge. …
DNA polymerases are proteins that synthesize new DNA strands using preexisting DNA strands as templates. Before one cell divides to produce two cells, the DNA containing the genetic information in it must be duplicated for the new cell, in a process known as polymerization. In human cells, duplicating the DNA genome requires the polymerization of 2.91 billion nucleotides, the building blocks of DN…
DNA profiling is a molecular testing method used to uniquely identify people and other organisms. In many ways, it is similar to blood typing and fingerprinting, and it is sometimes called "DNA fingerprinting." Because every organism's DNA is unique, DNA can be examined to identify people who might be related to each other, to compare suspected criminals to DNA left at the sce…
When it was discovered that DNA is the macromolecular carrier of essentially all genetic information, it was assumed that DNA is extremely stable. Consequently, it came as something of a surprise to learn that DNA is actually unstable and subject to continual damage. When DNA damage is severe, the cell is unable to replicate and may die. Repair of DNA must be regarded as essential for the preserva…
DNA was discovered in the nineteenth century, but its significance as the physical basis of inheritance was not understood until midway through the twentieth. The realization that it was the molecule of heredity led to intensive efforts to determine its three-dimensional structure, and to understand how it stores and transmits genetic information. The discovery of the structure of DNA, and the el…
A DNA vaccine uses foreign DNA to express an encoded protein and stimulate the body's immune system. It represents a new way to immunize against infectious disease that is potentially less expensive than classic vaccination forms. …
Down syndrome, also called trisomy 21, is the single most common genetic cause of moderate mental retardation. It occurs in about one of every eight hundred live births. It is caused by the inheritance of an extra copy of chromosome 21. The condition was named after an English physician, J. Langdon Down, who in 1866 published the first report describing patients with similar facial features and me…
