Category Archives: Genetics

"Half of your DNA is determined by your mother's side, and half is by your father. So, if you seem to look exactly like your mother, perhaps some DNA that codes for your body and how your organs run was copied from your father's genes."

So close, yet so far. This quote, taken from a high school student's submission in a national essay contest, represents just one of countless misconceptions many people have about the basic nature of heredity and how our bodies read the instructions stored in our genetic material (Shaw et al. 2008). Although it is true that half of our genome is inherited from our mother and half from our father, it is certainly not the case that only some of our cells receive instructions from only some of our DNA. Rather, every diploid, nucleated cell in our body contains a full complement of chromosomes, and our specific cellular phenotypes are the result of complex patterns of gene expression and regulation.

In fact, it is through this dynamic regulation of gene expression that organismal complexity is determined. For example, when the first draft of the human genome was published in 2003, scientists were surprised to find that sequence analysis revealed only around 25,000 genes, instead of the 50,000 to 100,000 genes originally hypothesized. Clues from studies examining the genomic structure of a variety of organisms suggest that much of human uniqueness lies not in our number of genes, but instead in our regulatory control over when and where certain genes are expressed.

Additional examination of different organisms has revealed that all genomes are more complex and dynamic than previously thought. Thus, the central dogma proposed by Francis Crick as early as 1958 that DNA encodes RNA, which is translated into protein is now considered overly simplistic. Today, scientists know that beyond the three types of RNA that make the central dogma possible (mRNA, tRNA, and rRNA), there are many additional varieties of functional RNA within cells, many of which serve a number of known (and unknown) functions, including regulation of gene expression. Understanding how the structure of these and other nucleic acids belies their function at both the macroscopic and microscopic levels, and discovering how that understanding can be manipulated, is the essence of where genetics and molecular biology converge.

Detailed comparative analysis of different organisms' genomes has also shed light on the genetics of evolutionary history. Using molecular approaches, information about mutation rates, and other tools, scientists continue to add more detail to phylogenetic trees, which tell us about the relationships between the marvelous variety of organisms that have existed throughout the planet's history. Examining how different processes shape populations through the culling or maintenance of deleterious or beneficial alleles lies at the heart of the field of population genetics.

Within a population, beneficial alleles are typically maintained through positive natural selection, while alleles that compromise fitness are often removed via negative selection. Some detrimental alleles may remain, however, and a number of these alleles are associated with disease. Many common human diseases, such as asthma, cardiovascular disease, and various forms of cancer, are complex-in other words, they arise from the interaction between multiple alleles at different genetic loci with cues from the environment. Other diseases, which are significantly less prevalent, are inherited. For instance, phenylketonuria (PKU) was the first disease shown to have a recessive pattern of inheritance. Other conditions, like Huntington's disease, are associated with dominant alleles, while still other disorders are sex-linked-a concept that was first identified through studies involving mutations in the common fruit fly. Still other diseases, like Down syndrome, are linked to chromosomal aberrations that can be identified through cytogenetic techniques that examine chromosome structure and number.

Our understanding in all these fields has blossomed in recent years. Thanks to the merger of molecular biology techniques with improved knowledge of genetics, scientists are now able to create transgenic organisms that have specific characters, test embryos for a variety of traits in vitro, and develop all manner of diagnostic tests capable of identifying individuals at risk for particular disorders. This interplay between genetics and society makes it crucial for all of us to grasp the science behind these techniques in order to better inform our decisions at the doctor, at the grocery store, and at home.

As we seek to cultivate this understanding of modern genetics, it is critical to remember that the misconceptions expressed in the aforementioned essay are the same ones that many individuals carry with them. Thus, when working together, faculty and students need to explore not only what we know about genetics, but also what data and evidence support these claims. Only when we are equipped with the ability to reach our own conclusions will our misconceptions be altered.

-Kenna Shaw, Ph.D

Image: Mehau Kulyk/Science Photo Library/Getty Images.

Shaw, K. (2008) Genetics. Nature Education 2(10):1

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Genetics | Learn Science at Scitable

Dr. Melissa B. Davis is a native of Albany, Georgia. Her interest in the field of genetics was sparked by a summer research program at The Ohio State University, where she conducted spinal cord regeneration studies in the Tassava Lab in the department of molecular genetics. After her undergraduate studies, Dr. Davis completed her Ph.D. in the department of genetics at UGA in 2003.

Dr. Melissa B. Davis completed a postdoc fellowship with Dr. Kevin White at Yale School of Medicine in 2006. While there, she also served as a teaching coordinator of the Yale School of Medicine Summer Medical Education Program for visiting undergraduates, aiding in the pre-med training of over 300 undergraduates. She completed additional postdoctoral training in functional genomics and cancer disparities at the University of Chicago in 2009. Her work became part of the international ModEnCODE project, to delineate the regulatory elements of genes across the Drosophilia genome. In addition, Dr. Davis was a postdoctoral scholar at the University of Chicago's Center for Interdisciplinary Health Disparities Research. She began training with the center to conduct breast cancer disparities research under the guidance of Dr. Olufunmilayo Olopade, one of the world's leaders in global health and breast cancer disparities research. Her work with the center includes identification of associations of epigenetic cofactors with breast cancer subtypes that are predominantly found in women of African descent.

Following her postdoctoral training, Davis joined the inaugural GRU/UGA Medical Partnership faculty in 2009 as a genetics professor. Currently she is a tenure-track faculty member with the UGA Department of Genetics and serves in a dual role with the Medical Partnership. Her lab conducts research concerned with the molecular and environmental factors that impact the etiology of breast cancer subtypes. She is also investigating the role of ancestral genetics on predisposition to these tumor types and/or oncogene expression and function. For this work, Davis is collaborating with researchers in the UGA College of Public Health to uncover the environmental factors that impact epigenetic regulation of key metabolism, immunity, and cancer genes.

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Faculty & Staff | Directory | Medical Partnership

The recent sequencing of the human genome has accelerated scientific discoveries in genetics related to medicine and animal and plant science. Research universities in Georgia, supported by government funding and collaborations with private industry, conduct leading-edge research that contributes to improved prevention, diagnosis, and treatment of genetically caused diseases. The Georgia Research Alliance, a university, business, and government partnership, has been a key supporter of genetics research through eminent scholars, research laboratories and equipment, and technology incubators. Newborn Genetics Screening The state of Georgia has paid for newborn genetics screening since 1978. The program, developed in collaboration with the Emory University School of Medicine's Department of Human Genetics and Genetics Laboratory, tests all Georgia newborns for thirteen inherited diseases, including metabolic diseases. Emory, located in Atlanta, is one of the nation's leading research and treatment centers for inherited diseases, including lysosomal enzyme diseases, fragile X syndrome, and Down syndrome. Emory scientists are leaders in developing new enzyme replacement therapies for children born with Gaucher disease and Fabry disease, screening and treatment for maple syrup urine disease, and FISH technology (fluorescence in situ hybridization, which allows physicians to look for chromosomal abnormalities under a microscope). Emory's large staff of genetics counselors works with parents and prospective parents at centers throughout the state. In addition, genetics counseling and screening to predict adult cancers has developed rapidly since scientists discovered altered genes that increase the risk of breast, ovarian, and colon cancers. University Genetics Research Several of Georgia's research universities have extensive research centers focused on genetics. The Department of Human Genetics at the Emory University School of Medicine includes both laboratory research and clinical treatment programs in one of the largest academic genetics departments in the nation. Emory has the world's largest research program on fragile X syndrome to be funded by the National Institutes of Health (NIH). The gene responsible for fragile X syndrome, the most common cause of inherited mental retardation, was discovered by Emory professor Steven T. Warren, who led an international team of scientists. Warren and his team also have developed screening techniques and are working on potential new therapies for fragile X syndrome, which affects 3,500 individuals in Georgia either directly or as carriers. Emory geneticist Stephanie Sherman's discovery of what is known as the "Sherman Paradox," in which genetic diseases caused by the triplet repeat of amino acids are not passed on to offspring with the usual probabilities common among most genetic disorders, has been invaluable in helping physicians predict risk for these genetic diseases. Through support from the NIH, scientists at Emory and the Centers for Disease Control and Prevention have conducted sixteen years of research on the causes and clinical consequences of Down syndrome through the Atlanta Down Syndrome Project. All Atlanta-area newborns with Down syndrome and their parents are eligible to participate in the project. In 2000 the NIH expanded the Atlanta project into the National Down Syndrome Project by adding five other research centers (in Arkansas, California, Iowa, New Jersey, and New York). The Department of Genetics at the University of Georgia (UGA) in Athens includes many faculty who teach genetics to undergraduate and graduate students. Graduate research and training includes molecular genetics, evolutionary biology, and genomics. Four genetics faculty members are also members of the prestigious National Academy of Sciences.

The UGA Center for Applied Genetic Technologies (CAGT) brings together diverse expertise in plant and animal genomics, DNA markers, and transformation (a process of genetic alteration) and provides state-of-the-art facilities and instrumentation. Within CAGT are research labs and the Georgia BioBusiness Center incubator, which supports start-up companies in the biosciences by providing them access to management expertise and sophisticated instrumentation.

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Genetics in Georgia | New Georgia Encyclopedia

Human beings have cells with 46 chromosomes -- 2 chromosomes that determine what sex they are (X and Y chromosomes), and 22 pairs of nonsex (autosomal) chromosomes. Males are "46,XY" and females are "46,XX." The chromosomes are made up of strands of genetic information called DNA. Each chromosome contains sections of DNA called genes, which carry the information needed by your body to make certain proteins.

Each pair of autosomal chromosomes contains one chromosome from the mother and one from the father. Each chromosome in a pair carries basically the same information; that is, each chromosome pair has the same genes. Sometimes there are slight variations of these genes. These variations occur in less than 1% of the DNA sequence. The genes that have these variations are called alleles.

Some of these variations can result in a gene that is abnormal. An abnormal gene may lead to an abnormal protein or an abnormal amount of a normal protein. In a pair of autosomal chromosomes, there are two copies of each gene, one from each parent. If one of these genes is abnormal, the other one may make enough protein so that no disease develops. When this happens, the abnormal gene is called recessive, and the other gene in the pair is called dominant. Recessive genes are said to be inherited in an autosomal recessive pattern.

However, if only one abnormal gene is needed to produce a disease, it leads to a dominant hereditary disorder. In the case of a dominant disorder, if one abnormal gene is inherited from mom or dad, the child will likely show the disease.

A person with one abnormal gene is called heterozygous for that gene. If a child receives an abnormal recessive disease gene from both parents, the child will show the disease and will be homozygous (or compound heterozygous) for that gene.

GENETIC DISORDERS

Almost all diseases have a genetic component. However, the importance of that component varies. Disorders in which genes play an important role (genetic diseases) can be classified as:

A single-gene disorder (also called Mendelian disorder) is caused by a defect in one particular gene. Single gene defects are rare. But since there are about 4,000 known single gene disorders, their combined impact is significant.

Single-gene disorders are characterized by how they are passed down in families. There are six basic patterns of single gene inheritance:

The observed effect of a gene (the appearance of a disorder) is called the phenotype.

In autosomal dominant inheritance, the abnormality or abnormalities usually appear in every generation. Each time an affected woman has a child, that child has a 50% chance of inheriting the disease.

People with one copy of a recessive disease gene are called carriers. Carriers usually don't have symptoms of the disease. But, the gene can often be found by sensitive laboratory tests.

In autosomal recessive inheritance, the parents of an affected individual may not show the disease (they are carriers). On average, the chance that carrier parents could have children who develop the disease is 25% with each pregnancy. Male and female children are equally likely to be affected. For a child to have symptoms of an autosomal recessive disorder, the child must receive the abnormal gene from both parents. Because most recessive disorders are rare, a child is at increased risk of a recessive disease if the parents are related. Related individuals are more likely to have inherited the same rare gene from a common ancestor.

In X-linked recessive inheritance, the chance of getting the disease is much higher in males than females. Since the abnormal gene is carried on the X (female) chromosome, males do not transmit it to their sons (who will receive the Y chromosome from their fathers). However, they do transmit it to their daughters. In females, the presence of one normal X chromosome masks the effects of the X chromosome with the abnormal gene. So, almost all of the daughters of an affected man appear normal, but they are all carriers of the abnormal gene. Each time these daughters bear a son, there is a 50% chance the son will receive the abnormal gene.

In X-linked dominant inheritance, the abnormal gene appears in females even if there is also a normal X chromosome present. Since males pass the Y chromosome to their sons, affected males will not have affected sons. All of their daughters will be affected, however. Sons or daughters of affected females will have a 50% chance of getting the disease.

EXAMPLES OF SINGLE GENE DISORDERS

Autosomal recessive:

X-linked recessive:

Autosomal dominant:

X-linked dominant:

Only a few, rare, disorders are X-linked dominant. One of these is hypophosphatemic rickets, also called vitamin D -resistant rickets.

CHROMOSOMAL DISORDERS

In chromosomal disorders, the defect is due to either an excess or lack of the genes contained in a whole chromosome or chromosome segment.

Chromosomal disorders include:

MULTIFACTORIAL DISORDERS

Many of the most common diseasesare caused byinteractions of several genes and factors in the the environment (for example, illnesses in the mother and medications). These include:

MITOCHONDRIAL DNA-LINKED DISORDERS

Mitochondria are small organisms found in most of the body's cells. They are responsible for energy production inside cells. Mitochondria contain their own private DNA.

In recent years, many disorders have been shown to result from changes (mutations) in mitochondrial DNA. Because mitochondria come only from the female egg, most mitochondrial DNA-related disorders are passed down from the mother.

Mitochondrial DNA-related disorders can appear at any age. They have a wide variety of symptoms and signs. These disorders may cause:

Some other disorders are also known as mitochondrial disorders, but they do not involve mutations in the mitochondrial DNA. These disorders are usually single gene defects and they follow the same pattern of inheritance as other single gene disorders.

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Genetics: MedlinePlus Medical Encyclopedia

What are genes?

Genes are the part of a body cell that contain the biological information that parents pass to their children. Genes control the growth and development of cells. Genes are contained in DNA (deoxyribonucleic acid), a substance inside the center (nucleus) of cells that contains instructions for the development of the cell.

You inherit half of your genetic information from your mother and the other half from your father. Genes, alone or in combination, determine what features (genetic traits) a person inherits from his or her parents, such as blood type, hair color, eye color, and other characteristics, including risks of developing certain diseases. Certain changes in genes or chromosomes may cause problems in various body processes or functions.

Many genes together make up larger structures within the cell called chromosomes. Each cell normally contains 23 pairs of chromosomes.

A human has 46 chromosomes (23 pairs). One chromosome from each pair comes from the mother, and one chromosome from each pair comes from the father. One of the 23 pairs determines your sex. These sex chromosomes are called X and Y.

Some genetic disorders are caused when all or part of a chromosome is missing or when an extra chromosome or chromosome fragment is present.

Genetic testing examines a DNA sample for gene changes, or it may analyze the number, arrangement, and characteristics of the chromosomes. Testing may be performed on samples of blood, semen, urine, saliva, stool, body tissues, bone, or hair.

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Genetics and Genetic Disorders and Diseases - WebMD

Full Prescribing Information

Indications and Important Safety Information, Including Boxed Warning

ADCETRIS Indications ADCETRIS (brentuximab vedotin) Injection for intravenous infusion has been granted accelerated approval by the U.S. Food & Drug Administration for two indications:

These indications are approved under accelerated approval based on overall response rate. An improvement in patient-reported outcomes or survival has not been established. Continued approval for these indications may be contingent upon verification and description of clinical benefit in confirmatory trials.

BOXED WARNING Progressive multifocal leukoencephalopathy (PML): JC virus infection resulting in PML and death can occur in patients receiving ADCETRIS.

Contraindication ADCETRIS is contraindicated with concomitant bleomycin due to pulmonary toxicity (e.g., interstitial infiltration and/or inflammation).

Warnings and Precautions

Adverse Reactions ADCETRIS was studied as monotherapy in 160 patients in two phase 2 trials. Across both trials, the most common adverse reactions (20%), regardless of causality, were neutropenia, peripheral sensory neuropathy, fatigue, nausea, anemia, upper respiratory tract infection, diarrhea, pyrexia, rash, thrombocytopenia, cough and vomiting.

Drug Interactions Concomitant use of strong CYP3A4 inhibitors or inducers, or P-gp inhibitors, has the potential to affect the exposure to monomethyl auristatin (MMAE).

Use in Specific Populations MMAE exposure and adverse reactions are increased in patients with moderate or severe hepatic impairment or severe renal impairment. Avoid use.

Full Prescribing Information, including Boxed WARNING - U.S.

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