Adenine (A) is one of four chemical bases in DNA, with the other three being cytosine (C), guanine (G), and thymine (T). Within the DNA molecule, adenine bases located on one strand form chemical bonds with thymine bases on the opposite strand. The sequence of four DNA bases encodes the cell’s genetic instructions. A form of adenine called adenosine triphosphate (ATP) serves as an energy storage molecule and is used to power many chemical reactions within the cell.
Alternate forms or varieties of a gene. The alleles for a trait occupy the same locus or position on homologous chromosomes and thus govern the same trait. However, because they are different, their action may result in different expressions of that trait.
Small molecules that are the components of proteins. There are 20 different kinds of amino acids in living things. Proteins are composed of different combinations of amino acids assembled in chain-like molecules. Amino acids are primarily composed of carbon, oxygen, hydrogen, and nitrogen.
Transabdominal or transuterine aspiration of amniotic fluid usually performed during the second trimester of pregnancy, for instance in the process of prenatal diagnosis of a genetic disease.
Situation when one or more chromosomes, missing or in excess of the normal modal number, is considered a deviation from the 2n ratio.
A chromosome not involved in sex determination. The diploid human genome consists of 46 chromosomes, 22 pairs of autosomes, and 1 pair of sex chromosomes: the X and Y chromosomes.
The first breast cancer genes to be identified. Mutated forms of these genes are believed to be responsible for about half the cases of inherited breast cancer, especially those that occur in younger women. Both are tumour suppressor genes.
A base pair is two chemical bases bonded to one another forming a "rung of the DNA ladder." The DNA molecule consists of two strands that wind around each other like a twisted ladder. Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups. Attached to each sugar is one of four bases--adenine (A), cytosine (C), guanine (G), or thymine (T). The two strands are held together by hydrogen bonds between the bases, with adenine forming a base pair with thymine, and cytosine forming a base pair with guanine.
Bioinformatics is a subdiscipline of biology and computer science concerned with the acquisition, storage, analysis, and dissemination of biological data, most often DNA and amino acid sequences. Bioinformatics uses computer programs for a variety of applications, including determining gene and protein functions, establishing evolutionary relationships, and predicting the three-dimensional shapes of proteins.
A set of biological techniques developed through basic research and now applied to research and product development. In particular, the use by industry of recombinant DNA, cell fusion, and new bioprocessing techniques.
Cancer is a group of diseases characterized by uncontrolled cell growth. Cancer begins when a single cell mutates, resulting in a breakdown of the normal regulatory controls that keep cell division in check. These mutations can be inherited, caused by errors in DNA replication, or result from exposure to harmful chemicals. A cancerous tumor can spread to other parts of the body and, if left untreated, be fatal.
A cell is the basic building block of living things. All cells can be sorted into one of two groups: eukaryotes and prokaryotes. A eukaryote has a nucleus and membrane-bound organelles, while a prokaryote does not. Plants and animals are made of numerous eukaryotic cells, while many microbes, such as bacteria, consist of single cells. An adult human body is estimated to contain between 10 and 100 trillion cells.
A chromosome anomaly can be constitutional, acquired, homogenous, mosaic, numerical, structural.
A chromosome is an organized package of DNA found in the nucleus of the cell. Different organisms have different numbers of chromosomes. Humans have 23 pairs of chromosomes--22 pairs of numbered chromosomes, called autosomes, and one pair of sex chromosomes, X and Y. Each parent contributes one chromosome to each pair so that offspring get half of their chromosomes from their mother and half from their father.
Cytoplasm is the gelatinous liquid that fills the inside of a cell. It is composed of water, salts, and various organic molecules. Some intracellular organelles, such the nucleus and mitochondria, are enclosed by membranes that separate them from the cytoplasm.
Cytosine (C) is one of four chemical bases in DNA, the other three being adenine (A), guanine (G), and thymine (T). Within the DNA molecule, cytosine bases located on one strand form chemical bonds with guanine bases on the opposite strand. The sequence of four DNA bases encodes the cell’s genetic instructions.
DNA (deoxyribonucleic acid) is a large organic molecule that stores the genetic code for the synthesis of proteins. DNA is composed of sugars, phosphates and bases arranged in a double helix shaped molecular structure. Segments of DNA in chromosomes correspond to specific genes.
DNA sequencing is a laboratory technique used to determine the exact sequence of bases (A, C, G, and T) in a DNA molecule. The DNA base sequence carries the information a cell needs to assemble protein and RNA molecules. DNA sequence information is important to scientists investigating the functions of genes. The technology of DNA sequencing was made faster and less expensive as a part of the Human Genome Project.
De novo mutation
Spontaneously occurring mutation.
Deletion is a type of mutation involving the loss of genetic material. It can be small, involving a single missing DNA base pair, or large, involving a piece of a chromosome.
Double helix is the description of the structure of a DNA molecule. A DNA molecule consists of two strands that wind around each other like a twisted ladder. Each strand has a backbone made of alternating groups of sugar (deoxyribose) and phosphate groups. Attached to each sugar is one of four bases: adenine (A), cytosine (C), guanine (G), or thymine (T). The two strands are held together by bonds between the bases, adenine forming a base pair with thymine, and cytosine forming a base pair with guanine.
Down syndrome is a genetic disease resulting from a chromosomal abnormality. An individual with Down syndrome inherits all or part of an extra copy of Chromosome 21. Symptoms associated with the syndrome include mental retardation, distinctive facial characteristics, and increased risk for heart defects and digestive problems, which can range from mild to severe. The risk of having a child with Down syndrome rises with the mother’s age at the time of conception.
Fetus before the end of the third month.
An enzyme is a biological catalyst and is almost always a protein. It speeds up the rate of a specific chemical reaction in the cell. The enzyme is not destroyed during the reaction and is used over and over. A cell contains thousands of different types of enzyme molecules, each specific to a particular chemical reaction.
Epigenetics is an emerging field of science that studies heritable changes caused by the activation and deactivation of genes without any change in the underlying DNA sequence of the organism. The word epigenetics is of Greek origin and literally means over and above (epi) the genome.
Fraternal twins are also dizygotic twins. They result from the fertilization of two separate eggs during the same pregnancy. Fraternal twins may be of the same or different sexes. They share half of their genes just like any other siblings. In contrast, twins that result from the fertilization of a single egg that then splits in two are called monozygotic, or identical, twins. Identical twins share all of their genes and are always the same sex.
units of inheritance usually occurring at specific locations, or loci, on a chromosome. Physically, a gene is a sequence of DNA bases that specify the order of amino acids in an entire protein or, in some cases, a portion of a protein. A gene may be made up of hundreds of thousands of DNA bases. Genes are responsible for the hereditary traits in plants and animals.
the study of gene structure and action and the patterns of inheritance of traits from parent to offspring. Genetic mechanisms are the underlying foundation for evolutionary change. Genetics is the branch of science that deals with the inheritance of biological characteristics.
The full genetic complement of an individual (or of a species). In humans, it is estimated that each individual possesses approximately 2.9 billion base units in his or her DNA.
Determination of the order in which the bases are arranged within a length of DNA or RNA or, the sequence of amino acids that make up a protein.
Genomics is a discipline in genetics that applies DNA sequencing methods, and bioinformatics to sequence, assemble, and analyze the function and structure of genomes.
The genetic makeup of an individual. Genotype can refer to an organism’s entire genetic makeup or the alleles at a particular locus.
Guanine (G) is one of four chemical bases in DNA, with the other three being adenine (A), cytosine (C), and thymine (T). Within the DNA molecule, guanine bases located on one strand form chemical bonds with cytosine bases on the opposite strand. The sequence of four DNA bases encodes the cell’s genetic instructions.
Human Genome Project
A multinational research effort designed to identify and map the location of all human genes. The idea of a Human Genome Project began at a 1984 international conference in Utah. Research to decode the human genome began in earnest in 1986, funded by the U.S. Department of Energy. The initial stage of discovering all human DNA codons was completed early in 2001 at a cost of 2.7 billion dollars. Completed in April 2003, data from the project are freely available to researchers and others interested in genetics and human health.
The process of joining two complementary strands of DNA or one each of DNA and RNA to form a double-stranded molecule.
IVF, in vitro fertilization
Fertilization of the ovum by a sperm outside of the living organism.
Identical twins are also known as monozygotic twins. They result from the fertilization of a single egg that splits in two. Identical twins share all of their genes and are always of the same sex. In contrast, fraternal, or dizygotic, twins result from the fertilization of two separate eggs during the same pregnancy. They share half of their genes, just like any other siblings. Fraternal twins can be of the same or different sexes.
A karyotype is an individual’s collection of chromosomes. The term also refers to a laboratory technique that produces an image of an individual’s chromosomes. The karyotype is used to look for abnormal numbers or structures of chromosomes.
A locus is the specific physical location of a gene or other DNA sequence on a chromosome, like a genetic street address. The plural of locus is "loci".
A lymphocyte is a type of white blood cell that is part of the immune system. There are two main types of lymphocytes: B cells and T cells. The B cells produce antibodies that are used to attack invading bacteria, viruses, and toxins. The T cells destroy the body’s own cells that have themselves been taken over by viruses or become cancerous.
Mapping is the process of making a representative diagram cataloging the genes and other features of a chromosome and showing their relative locations. Cytogenetic maps are made using photomicrographs of chromosomes stained to reveal structural variations. Genetic maps use the idea of linkage to estimate the relative locations of genes. Physical maps, made using recombinant DNA (rDNA) technology, show the actual physical locations of landmarks along a chromosome.
Unit of length for DNA fragments equal to 1 million nucleotides and roughly equal to 1 cM.
Inheritance patterns which can be explained by simple rules of dominance and recessiveness of genes.
Messenger RNA (mRNA) is a single-stranded RNA molecule that is complementary to one of the DNA strands of a gene. The mRNA is an RNA version of the gene that leaves the cell nucleus and moves to the cytoplasm where proteins are made. During protein synthesis, an organelle called a ribosome moves along the mRNA, reads its base sequence, and uses the genetic code to translate each three-base triplet, or codon, into its corresponding amino acid.
Mitochondrial DNA is the small circular chromosome found inside mitochondria. The mitochondria are organelles found in cells that are the sites of energy production. The mitochondria, and thus mitochondrial DNA, are passed from mother to offspring.
Mitosis is a cellular process that replicates chromosomes and produces two identical nuclei in preparation for cell division. Generally, mitosis is immediately followed by the equal division of the cell nuclei and other cell contents into two daughter cells.
Study of molecules carrying the hereditary message, DNA, RNA structure, synthesis, modifications or transformations.
Branch of genetics concerned with the molecular structure and activities of the genetic material, including the replication of DNA, the transcription into RNA and the translation of RNA to form proteins.
Monosomy is the state of having a single copy of a chromosome pair instead of the usual two copies found in diploid cells. Monosomy can be partial if a portion of the second chromosome copy is present. Monosomy, or partial monosomy, is the cause of some human diseases such as Turner syndrome and Cri du Chat syndrome.
A mutation is a change in a DNA sequence. Mutations can result from DNA copying mistakes made during cell division, exposure to ionizing radiation, exposure to chemicals called mutagens, or infection by viruses. Germ line mutations occur in the eggs and sperm and can be passed on to offspring, while somatic mutations occur in body cells and are not passed on.
Nanotechnology is the science of manipulating matter on the atomic and molecular scales to solve problems. Nanotechnology is a developing applied science that has the potential to make significant contributions to many fields, including engineering, computer science, and medicine.
A nucleus is a membrane-bound organelle that contains the cell’s chromosomes. Pores in the nuclear membrane allow for the passage of molecules in and out of the nucleus.
An oncogene is a mutated gene that contributes to the development of a cancer. In their normal, unmuted state, oncogenes are called proto-oncogenes, and they play roles in the regulation of cell division. Some oncogenes work like putting your foot down on the accelerator of a car, pushing a cell to divide. Other oncogenes work like removing your foot from the brake while parked on a hill, also causing the cell to divide.
An organelle is a subcellular structure that has one or more specific jobs to perform in the cell, much like an organ does in the body. Among the more important cell organelles are the nuclei, which store genetic information; mitochondria, which produce chemical energy; and ribosomes, which assemble proteins.
Personalized medicine is an emerging practice of medicine that uses an individual’s genetic profile to guide decisions made in regard to the prevention, diagnosis, and treatment of disease. Knowledge of a patient’s genetic profile can help doctors select the proper medication or therapy and administer it using the proper dose or regimen. Personalized medicine is being advanced through data from the Human Genome Project.
A phenotype is an individual’s observable traits, such as height, eye color, and blood type. The genetic contribution to the phenotype is called the genotype. Some traits are largely determined by the genotype, while other traits are largely determined by environmental factors.
A polygenic trait is one whose phenotype is influenced by more than one gene. Traits that display a continuous distribution, such as height or skin color, are polygenic. The inheritance of polygenic traits does not show the phenotypic ratios characteristic of Mendelian inheritance, though each of the genes contributing to the trait is inherited as described by Gregor Mendel. Many polygenic traits are also influenced by the environment and are called multifactorial.
Polymerase Chain Reaction
Polymerase chain reaction (PCR) is a laboratory technique used to amplify DNA sequences. The method involves using short DNA sequences called primers to select the portion of the genome to be amplified. The temperature of the sample is repeatedly raised and lowered to help a DNA replication enzyme copy the target DNA sequence. The technique can produce a billion copies of the target sequence in just a few hours.
Precision medicine is a field of medicine that entails predicting the probability of disease and instituting preventive measures in order to either prevent the disease altogether or significantly decrease its impact upon the patient (such as by preventing mortality or limiting morbidity).
Any of a large number of complex organic molecules that are composed of one or more chains of amino acids. Proteins can serve a wide variety of functions through their ability to bind to other molecules. Proteins may be enzymes, hormones, antibodies, structural components, or gas-transporting molecules.
RNA (Ribonucleic Acid)
Ribonucleic acid (RNA) is a molecule similar to DNA. Unlike DNA, RNA is single-stranded. An RNA strand has a backbone made of alternating sugar (ribose) and phosphate groups. Attached to each sugar is one of four bases--adenine (A), uracil (U), cytosine (C), or guanine (G). Different types of RNA exist in the cell: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). More recently, some small RNAs have been found to be involved in regulating gene expression.
A ribosome is a cellular particle made of RNA and protein that serves as the site for protein synthesis in the cell. The ribosome reads the sequence of the messenger RNA (mRNA) and, using the genetic code, translates the sequence of RNA bases into a sequence of amino acids.
A sex chromosome is a type of chromosome that participates in sex determination. Humans and most other mammals have two sex chromosomes, the X and the Y. Females have two X chromosomes in their cells, while males have both X and a Y chromosome in their cells. Egg cells all contain an X chromosome, while sperm cells contain an X or Y chromosome. This arrangement means that it is the male that determines the sex of the offspring when fertilization occurs.
Shotgun sequencing is a laboratory technique for determining the DNA sequence of an organism’s genome. The method involves breaking the genome into a collection of small DNA fragments that are sequenced individually. A computer program looks for overlaps in the DNA sequences and uses them to place the individual fragments in their correct order to reconstitute the genome.
Susceptibility is a condition of the body that increases the likelihood that the individual will develop a particular disease. Susceptibility is influenced by a combination of genetic and environmental factors.
A syndrome is a collection of recognizable traits or abnormalities that tend to occur together and are associated with a specific disease.
Thymine (T) is one of four chemical bases in DNA, the other three being adenine (A), cytosine (C), and guanine (G). Within the DNA molecule, thymine bases located on one strand form chemical bonds with adenine bases on the opposite strand. The sequence of four DNA bases encodes the cell’s genetic instructions.
Tumor suppressor gene
A tumor suppressor gene directs the production of a protein that is part of the system that regulates cell division. The tumor suppressor protein plays a role in keeping cell division in check. When mutated, a tumor suppressor gene is unable to do its job, and as a result uncontrolled cell growth may occur. This may contribute to the development of a cancer.
A virus is an infectious agent that occupies a place near the boundary between the living and the nonliving. It is a particle much smaller than a bacterial cell, consisting of a small genome of either DNA or RNA surrounded by a protein coat. Viruses enter host cells and hijack the enzymes and materials of the host cells to make more copies of themselves. Viruses cause a wide variety of diseases in plants and animals, including AIDS, measles, smallpox, and polio.
The X chromosome is one of two sex chromosomes. Humans and most mammals have two sex chromosomes, the X and Y. Females have two X chromosomes in their cells, while males have X and Y chromosomes in their cells. Egg cells all contain an X chromosome, while sperm cells contain an X or a Y chromosome. This arrangement means that during fertilization, it is the male that determines the sex of the offspring.
The Y chromosome is one of two sex chromosomes. Humans and other mammals have two sex chromosomes, the X and the Y. Females have two X chromosomes in their cells, while males have X and Y chromosomes in their cells. Egg cells contain an X chromosome, while sperm cells contain an X or a Y chromosome. This arrangement means that during fertilization, it is the male that determines the sex of the offspring.
*Reference: National Human Genome Research Institute