Human genetics, study of the inheritance of characteristics by children from parents. Inheritance in humans does not differ in any fundamental way from that in other organisms.
The study of human heredity occupies a central position in genetics. Much of this interest stems from a basic desire to know who humans are and why they are as they are. At a more practical level, an understanding of human heredity is of critical importance in the prediction, diagnosis, and treatment of diseases that have a genetic component. The quest to determine the genetic basis of human health has given rise to the field of medical genetics. In general, medicine has given focus and purpose to human genetics, so the terms medical genetics and human genetics are often considered synonymous.
A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorders are the most common, the term is mostly used when discussing disorders with a single genetic cause, either in a gene or chromosome.The mutation responsible can occur spontaneously before embryonic development (a de novo mutation), or it can be inherited from two parents who are carriers of a faulty gene (autosomal recessive inheritance) or from a parent with the disorder (autosomal dominant inheritance). When the genetic disorder is inherited from one or both parents, it is also classified as a hereditary disease. Some disorders are caused by a mutation on the X chromosome and have X-linked inheritance. Very few disorders are inherited on the Y chromosome or mitochondrial DNA.
Gene therapy is an experimental technique that uses genes to treat or prevent disease. In the future, this technique may allow doctors to treat a disorder by inserting a gene into a patient’s cells instead of using drugs or surgery. Researchers are testing several approaches to gene therapy, including:
Although gene therapy is a promising treatment option for a number of diseases (including inherited disorders, some types of cancer, and certain viral infections), the technique remains risky and is still under study to make sure that it will be safe and effective. Gene therapy is currently being tested only for diseases that have no other cures.
Molecular genetics is the study of the processes whereby biological information is stored, copied, repaired and decoded to create protein and other molecules within cells and tissues.
This influential area of bioscience contributes significantly to expanding our understanding of biology and allows us to develop bespoke diagnosis, treatment and disease prevention for each patient based on their own genetic make-up.
Medical genetics is the branch of medicine that involves the diagnosis and management of hereditary disorders. Medical genetics differs from human genetics in that human genetics is a field of scientific research that may or may not apply to medicine, while medical genetics refers to the application of genetics to medical care. For example, research on the causes and inheritance of genetic disorders would be considered within both human genetics and medical genetics, while the diagnosis, management, and counselling people with genetic disorders would be considered part of medical genetics.
In contrast, the study of typically non-medical phenotypes such as the genetics of eye color would be considered part of human genetics, but not necessarily relevant to medical genetics (except in situations such as albinism). Genetic medicine is a newer term for medical genetics and incorporates areas such as gene therapy, personalized medicine, and the rapidly emerging new medical specialty, predictive medicine.
Epigenetics is the study of how your behaviors and environment can cause changes that affect the way your genes work. Unlike genetic changes, epigenetic changes are reversible and do not change your DNA sequence, but they can change how your body reads a DNA sequence.
Gene expression refers to how often or when proteins are created from the instructions within your genes. While genetic changes can alter which protein is made, epigenetic changes affect gene expression to turn genes “on” and “off.” Since your environment and behaviors, such as diet and exercise, can result in epigenetic changes, it is easy to see the connection between your genes and your behaviors and environment.
Genomics is an interdisciplinary field of biology focusing on the structure, function, evolution, mapping, and editing of genomes. A genome is an organism's complete set of DNA, including all of its genes. In contrast to genetics, which refers to the study of individual genes and their roles in inheritance, genomics aims at the collective characterization and quantification of all of an organism's genes, their interrelations and influence on the organism. Genes may direct the production of proteins with the assistance of enzymes and messenger molecules. In turn, proteins make up body structures such as organs and tissues as well as control chemical reactions and carry signals between cells. Genomics also involves the sequencing and analysis of genomes through uses of high throughput DNA sequencing and bioinformatics to assemble and analyze the function and structure of entire genomes. Advances in genomics have triggered a revolution in discovery-based research and systems biology to facilitate understanding of even the most complex biological systems such as the brain.
Cytogenetics is the branch of genetics that studies the structure of DNA within the cell nucleus. This DNA is condensed during cell division and form chromosomes. The cytogenetic studies the number and morphology of chromosomes. Using chromosome banding techniques (classical cytogenetics) or hybridization fluorescently labeled probes (molecular cytogenetics). The number and morphology of chromosomes in a cell of a particular species are always constant, in most cells of the body (with the exception of reproductive cells and others such as the liver). This is a characteristic of each specie, in humans such as the number of chromosomes is 46.
The study of chromosomes, which are long strands of DNA and protein that contain most of the genetic information in a cell. Cytogenetics involves testing samples of tissue, blood, or bone marrow in a laboratory to look for changes in chromosomes, including broken, missing, rearranged, or extra chromosomes. Changes in certain chromosomes may be a sign of a genetic disease or condition or some types of cancer. Cytogenetics may be used to help diagnose a disease or condition, plan treatment, or find out how well treatment is working.
Genetic counseling is the process of advising individuals and families affected by or at risk of genetic disorders to help them understand and adapt to the medical, psychological and familial implications of genetic contributions to disease; this field is considered necessary for the implementation of genomic medicine. The process integrates:
Biochemical genetics involves diagnosing and treating metabolic diseases. These are problems with how the body makes, breaks down or uses proteins, fats or carbohydrates. They are caused by genes that are not normal and cannot make the enzymes the body needs. (Enzymes are found in the blood, organs, saliva and other parts of the body. They are important to all bodily functions.) These diseases are called inborn errors of metabolism.
Developmental genetics is the study of how genes control the growth and development of an organism throughout its life-cycle.The function of genes is to pass on the information necessary to build proteins - and bodies - from one generation to the next. A newly fertilised egg cell has a collection of genes that contains all information needed to transform it from a single cell into an embryo and then an adult. The process that changes a single cell into a new person (or a new frog, or a new oak tree) is called development. During the course of development, complex structures develop from simple ones. A single cell transforms itself into an adult organism.
Creating an organism from a single cell involves three important processes:
Clinical genetics involves the study, counselling and treatment of individuals and families with heritable disorders and disease predisposition. Diagnostic tools include standard ontologies for describing dysmorphology and traits, pedigree analysis, disease locus mapping by linkage or homozygosity, karyotyping, genome sequencing and genotyping.
Cancer is a common disease, and almost every family has a number of members who suffer from cancer. However, this does not generally mean that families have a hereditary predisposition to cancer. The vast majority of cancer cases originate from the combined effect of hereditary as well as external influences, such as environmental and lifestyle factors.
Cancer is not inherited. It is only the genetic defect that can lead to cancer that is inherited, which means that the predisposition to getting cancer, or increased risk, can be inherited. However, this is not common. According to current estimates, only about one in 10 cases of cancer is associated with hereditary predisposition.
An inherited genetic defect is not necessarily passed on to all members of the same family, and not everyone who receives the same defective gene will develop cancer. It is also worth remembering that the genetic changes that occur in cancerous tumours are not passed on genetically to one’s offspring.
Pharmacogenetics is the study of the genetic basis of interindividual patient variability in the response to drug therapy. Pharmacogenetics allows for individualization of drug therapy.
Pharmacogenomics is closely related to pharmacogenetics and is considered to be an equivalent or overlapping field. Pharmacogenomics involves study of the role of genes and their genetic variations (DNA, RNA level) in the molecular basis of disease and the resulting pharmacologic impact of drugs on that disease. Pharmacogenomics is sometimes defined to include drug design aimed at variants of a pharmacologic target. Pharmacogenetics and pharmacogenomics are both important disciplines involved in the study of genes that code for drug-metabolizing enzymes, drug receptors, drug transporters, and ion channels or efflux systems.
Immunity is the ability of an individual to recognize the “self” molecules that make up one’s own body and to distinguish them from such “nonself” molecules as those found in infectious microorganisms and toxins. This process has a prominent genetic component. Knowledge of the genetic and molecular basis of the mammalian immune system has increased in parallel with the explosive advances made in somatic cell and molecular genetics.
There are two major components of the immune system, both originating from the same precursor “stem” cells. The bursa component provides B lymphocytes, a class of white blood cells that, when appropriately stimulated, differentiate into plasma cells. These latter cells produce circulating soluble proteins called antibodies or immunoglobulins. Antibodies are produced in response to substances called antigens, most of which are foreign proteins or polysaccharides. An antibody molecule can recognize a specific antigen, combine with it, and initiate its destruction. This so-called humoral immunity is accomplished through a complicated series of interactions with other molecules and cells; some of these interactions are mediated by another group of lymphocytes, the T lymphocytes, which are derived from the thymus gland. Once a B lymphocyte has been exposed to a specific antigen, it “remembers” the contact so that future exposure will cause an accelerated and magnified immune reaction. This is a manifestation of what has been called immunological memory.