Prenatal Genetic Testing

Prenatal (before birth) genetic testing refers to testing the fetus for a potential genetic condition. The pregnant woman is considered the patient and makes decisions regarding prenatal testing. There are a variety of circumstances under which a woman might be offered prenatal genetic testing. The parents of the fetus may have a genetic disorder, or they may be what is known as carriers. An abnormality or birth defect may be detected on ultrasound that could indicate a genetic condition. The...

Presymptomatic Testing of Children

Presymptomatic testing of children has somewhat different considerations. It is typically considered only when the onset of the disorder occurs in childhood, or when knowing the genetic status will significantly benefit the child, for example by enabling him to receive early preventive treatment. For example, children at risk for inheriting the gene that causes retinoblastoma (cancer of the retina) may be tested because the disease usually presents before age five. With early treatment, the...

Autosomal Dominant Inheritance

Autosomal dominant inheritance is due to a dominant allele carried on one of the autosomes. Autosomal dominant alleles need only be inherited from one parent, either the mother or the father, in order to be expressed in the phenotype. Because of this, any child has a 50 percent chance of inheriting the allele and expressing the trait if one parent has it. Many normal human traits are due to autosomal dominant alleles, including the presence of dimples, a cleft chin, and a widow's-peak hairline....

Treatment Options and Continuing Research

Blood transfusions have been a common therapy for severe thalassemia, but transfusions do not cure the disease, and frequent transfusions can cause iron overload, an illness caused by excessively high levels of iron. A drug, called an iron chelator, may be given to bind with the excess iron. Iron chelators can produce additional side effects, such as hearing loss and reduced growth. As with sickle cell disease, gene therapy and bone marrow transplants are very promising therapies for severe...

Origins of the Human Genome Project

One could say that the Human Genome Project really began in 1953, when James Watson and Francis Crick deduced the molecular structure of DNA, the molecule of which the genome is made. (Watson and Crick were awarded the Nobel Prize for this work in 1962.) Since that time, scientists have wanted to know the complete sequence of a gene, and even dreamed that some day it would be possible to determine the complete sequence of all of the genes in any organism, including humans. The original impetus...

Many Roles Many Rewards

Epidemiologists interested in the influence of genetic factors on health may play several types of roles on a research project, including assisting in the overall design of the study, developing instruments to collect nongenetic risk-factor data, and using that data to investigate possible interactions between genetic and nongenetic (environmental) factors that influence health. Genetic epidemiologists perform a similar role, using study designs and statistical approaches developed specifically...

Positive and Negative Eugenics

Galton identified positive and negative eugenics as the two basic methods to improve humanity. Positive eugenics used education, tax incentives, and childbirth stipends to encourage procreation among fit people. Education would convince fit parents to have more children, out of a desire to increase the common good. Lower taxes on larger families and the provision of a small birth payment for each eugenic child would provide further inducements. Conversely, eugenically educated but unfit people...

Genetic Characteristics of Founder Populations

Because the founder population is small, genetic drift can play an important role in determining the genetic makeup of subsequent generations, and allele frequencies may fluctuate. For example, consider an extreme situation where a new population is founded by just two individuals, a male and a female, perhaps because they are stranded on an island. Assume that the mother is heterozygous for a particular allele (Aa), while the father is homozygous (AA). If the couple has two children, there is...

Longevity of Gene Expression

One of the most challenging problems in gene therapy is to achieve long-lasting expression of the therapeutic gene, also called the transgene. Often the virus used to deliver the transgene causes the patient's body to produce an immune response that destroys the very cells that have been treated. This is especially true when an adenovirus is used to deliver genes. The human body raises a potent immune response to prevent or limit infections by adenovirus, completely clearing it from the body...

Eukaryotic Genes

In eukaryotic cells, genes are more complex. It was discovered in 1977 that eukaryotic genes are functionally separated into coding segments called exons, which are interrupted by noncoding sequences of DNA called introns. The entire region between the initiation and termination sites is transcribed, including the introns, to form the primary transcript. This must then be processed by special enzymes that cut out the introns and splice together the exons to form an mRNA. The mRNA is then...

The Uses of HTS Assays

Storing, processing, analyzing, and accessing the wealth of data generated in an HTS assay poses special problems, simply because there is so much of it. Bioinformatics strategies are used to develop databases relating chemical structure, target characteristics, and assay results, allowing researchers to learn more from their results than just whether or not a particular compound was successful. Analyzing the common features of successful compounds may lead to rational development of better...

Puzzling Inheritance Pattern

While the location of this fragile site established that fragile X syndrome was indeed X-linked, inheritance of this disorder was clearly not typical of other X-linked disorders. At first, it was believed that fragile X syndrome was an X-linked recessive genetic disorder. However, there were many observations inconsistent with this inheritance pattern. If the disorder was truly inherited in an X-linked recessive manner, heterozygote carrier women would not display any characteristics of the...

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Chromosome Location Condition and Inheritance Pattern Common among European Jews. Lipid accumulation in liver, spleen, and bone marrow. Treat with Causes dwarfism. Most cases are new mutations, Expansion of a three-nucleotide portion of the gene causes late-onset neurodegeneration and death Multiple susceptibility alleles are known for this form of diabetes, a disorder of blood sugar regulation. Treated with dietary control and insulin HFE protein, involved in iron absorption Defect leads to...

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Because of their ablity to produce large amounts of offspring in a short amount of time, fruit flies were ideal specimens for early genetic experiments. metaphase stage in mitosis at which chromosomes are aligned along the cell equator several hundred times without separating from each other by mitosis and cell division. Instead, the newly replicated DNA strands line up parallel to one another to form a tight bundle, called polytene chromosomes. Polytene chromosomes are less condensed than...

Genetics of Eye Color

Differences in iris color have been attributed to such causes as the temperature of the brain and eyes. Some people have stressed differences between dark-eyed and light-eyed populations and have suggested that eye color is related to general traits such as temperament or intellect. But, toward the middle of the nineteenth century, it had become clear that iris color was due to iris pigment, that this pigment developed soon after birth, and that the final quantity and distribution of the...

IQ Tests

Conventional measures of intelligence are obtained using standard tests, called intelligence quotient tests or, more commonly, IQ tests. These tests have been shown to be reliable and valid. Reliability means that they measure the same thing from person to person, whereas validity means that they measure what they claim to measure. IQ tests measure a person's ability to reason and to solve problems. These abilities are frequently called general cognitive ability, or g. Almost all genetic...

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Genetically Modified Foods Plant Genetic Engineer Prenatal Diagnosis Transgenic Organisms Ethical Issues Lasse Lindahl University of Maryland, Baltimore Ribozyme RNA David E. Loren University of Pennsylvania School of Medicine Colon Cancer Dennis N. Luck Oberlin College Biotechnology Jeanne M. Lusher Wayne State University School of Medicine Children's Hospital of Michigan Hemophilia Kamrin T. MacKnight Medlen, Carroll, LLP Patent, Trademark and Copyright Attorneys Attorney Legal Issues...

Genes for Intelligence

The search for specific genes associated with IQ is proceeding at a rapid pace with the completion of the Human Genome Project. While defects in single genes, such as the fragile X gene, can cause mental retardation, the heritability of general cognitive ability is most likely due to multiple genes of small effect (called quantitative trait loci, or QTLs) rather than a single gene of large effect. QTLs contribute additively and interchangeably to intelligence. Genetic studies have identified...

Gene Regulation and Protein Synthesis

Gene expression in many bacteria is regulated through the existence of operons. An operon is a cluster of genes whose protein products have related functions. For instance, the lac operon includes one gene that transports lactose sugar into the cell and another that breaks it into two parts. These genes are under the control of the same promoter, and so are transcribed and translated into protein at the same time. RNA polymerase can only reach the promoter if a repressor is not blocking it the...

Overview of the Immune System

The immune system includes several interacting components. Nonspecific immunity (protection against any invasion) is provided by the barriers of the skin and mucous membranes lining the lungs and gut. Additional nonspecific defenses are provided by the inflammatory response and the complement proteins in the bloodstream. We shall not deal further with these defenses. Specific immunity is the set of defenses mounted against a specific invader. It involves the action of three major types of cells...

The Homologous Recombination Process

Homologous recombination is a process that occurs within the chromosome and which allows one piece of DNA to be exchanged for another piece. It is a cellular mechanism that is probably part of the normal process cells use to repair breaks in their chromosomes. Homologous recombina A modified version of the target gene replaces it in the chromosome. The target gene is removed and degraded. In this example, the gene is modified by insertion of an antibiotic resistance gene, which both inactivates...

The Future of Medicine

The idea of preventive medicine is not new, but until the completion of the Human Genome Project medicine did not have a way of accomplishing it for common medical problems. For example, for years almost every baby born in the United States has had its urine or blood screened early in life for phenylketonuria (PKU), a rare genetic disease in which affected individuals cannot metabolize the amino acid phenyalanine, a common amino acid in our food. Untreated, PKU patients develop severe mental...

Mendelian Inheritance Intelligence Testing and American Eugenics

Galton's eugenic ideas found fertile ground in America after 1900, when scientists rediscovered Mendel's findings regarding the inheritance of physical traits in pea plants. Mendel's notions of dominant and recessive genetic traits, easily identified in lower organisms such as plants and animals, convinced people that human eugenic improvement was possible. Scientists assumed that even complex human traits such as intelligence and behavior behaved as simple genetic unit characters, such as...

Protection as Well as Education

At the same time that they provide beneficial genetic counseling to patients and their families, professionals providing such a service must have a full understanding of the dangers of eugenics. The abuse of genetic information has led to many atrocities in the past. In Germany, the Nazis murdered nearly 7 million genetically defective people during World War II and forcibly sterilized nearly half a million others, all in the name of eugenics a policy that calls for the systematic elimination...

An Expanding Gene

In 1991 an international team of scientists identified the gene and mutation that causes fragile X syndrome. They found that in families with fragile X syndrome, there is a piece of the FMR1 gene, called a CGG repeat, which is abnormally expanded. In the general population, the repeat length can range from about six to fifty-four copies of the CGG, and the repeat is stable, or is passed from parent to child without change. In fragile X families, the premutation form of the repeat contains...