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Allele – any of two or more alternative forms of a gene that occupy the same locus on a chromosome.

Amino acids – a group of 20 different organic molecules when link together in various ways make up proteins. Each possesses both carboxyl and amino groups.

Anal stenosis – a narrowing or stricture of the anus.

Anemia - a reduction in the amount of oxygen-carrying red blood cells in hemoglobin or in total volume. The most common is a lack of iron in the body. It is also known as iron-poor blood

Aneuploidy - a chromosome problem that happens when one or more whole chromosomes either are missing or are present in
more than the typical number of copies.

Antisense – the complementary strand of DNA or RNA coding sequence, which pairs with a specific messenger RNA blocking it from being translated into protein and serving to inhibit gene function.

Aorta - the large artery that receives blood from the left ventricle and carries that blood to the branch arteries for distribution to the body.

Aortic valve - the semilunar valve between the left ventricle and the aorta. It prevents blood from flowing back into the ventricle. It consists of three flaps, or cusps.

Arrhythmia (Dysrhythmia) - an abnormal rhythm of the heart either in time or force. It is caused by disturbances in the movement of electrical impulses through the heart.

Artery - any one of a series of elastic walled vessels that carry blood from the heart to the body.

Atresia - the absence or closure of a normal opening in the body

Atrium - either one of the two upper chambers of the heart. Blood collects here before being passed to the ventricles. Also known as auricle.

Atrial fibrillation - rapid, uneven contractions in atria, which causes a lack of synchronism between heartbeat and pulse beat .

Autosomal dominant- a person who is affected possesses one copy of a normal allele and one copy of a mutant allele. This person has a 50-50 chance of passing along the mutant allele


Base pair – one of a pair of nucleotide bases (a purine and pyrimidine) on complementary strands of DNA or RNA. (ex. A-T or G-C pairs)

Bifid uvula – a disfiguration (usually cleft or split) of the uvula, the small mass that hangs at the back of the soft palate.

Birth defect- any defect present at birth; sometimes referred to as congenital.

Blood pressure - the pressure exerted by the heart in pumping blood; pressure of the blood in the arteries


Calcium – the most abundant mineral in the body. It is an essential element taken in through the diet. It is has several functions in the body, such as muscle contraction, heart function, and bone strength.

Candidate gene - a gene that is thought to cause or play a part in a disease.

Cardiac - pertaining to the heart.

Cardiac arrest - when the heart stops beating, either temporarily or permanently

Cardiologist - a doctor who diagnoses and treats heart problems.

Cardiology - the study of the heart and its functions in health and disease.

Cardiovascular - pertaining to the heart and blood vessels.

Carrier - an individual who carries a pathogen or a gene that causes a disease, but does not display symptoms of that diseases. This person may pass on the pathogen or gene thereby infecting another individual.

Cell - the smallest building unit of the animals, plants, and human beings.

Chromosome - Chromosomes carry the genetic material of most organisms and are organized into a number of linear structures.

Codon – any 3 bases (nucleotides) in a strand of DNA or mRNA that make up an amino acid or a termination signal. The basic unit of the genetic code.

Congenital - any trait or condition (mental or physical traits, diseases, anomalies, malformations, etc.) existing at birth. May be inherited or the result of an occurrence during the time of gestation up to birth.

Constipation – infrequent or abnormally delayed movement of the bowels. The feces is often dry and hardened

Coronary arteries - two arteries arising from the aorta that arch down over the top of the heart, branch out and provide blood to the working heart muscle.


Deletion - a chromosome alteration resulting in the loss of a piece of the genetic material, and therefore, the genetic information the segment contains.

DNA (deoxyribonucleic acid) - Genetic information is coded in the DNA. The DNA carries all the instructions for life and development. For example, DNA controls how many fingers we have, where our legs are placed on our body, and the color of our skin.

Dominant – a gene that almost always results in a specific characteristic, even when the person’s genome only contains one copy.

Dominant allele – In a heterozygote, the allele that is fully expressed in the phenotype.

Duplication - occurs when there are two copies of the same genetic material in a genome, this can be a gene or and entire chromosome.

Diastolic pressure - the pressure of blood inside arteries when the heart is at rest. In a blood pressure reading, it is the bottom number.


Ear infection – a blockage of the auditory tube in the middle ear that causes bacteria to build up and resulting in an infection. Usually treated with antibiotics.

Encopresis - involuntary bowel movement

Enuresis - involuntary urination

Exon – the part of a DNA sequence that codes for MRNA translation into a protein. Exons are flanked by introns.


Facial features - pertaining to parts that make up the face, such as the nose, lips, eyes, etc.

Family history - includes the medical history of a person’s immediate family. It is often used in an attempt to sort out possible hereditary tendencies toward a particular disease

Feeding - eating, giving food or nourishment.

FISH (Fluorescent In-Situ Hybridization) - a technique that uses fluorescent markers to detect changes in the genetic material.

Function – the specific action or physiological property of an organ or part of the body.


Gene - portion of DNA that determines a characteristic of an organism. Human beings have around 100,000 genes.

Gene amplification – selective synthesis of DNA, causing multiple copies of a single gene to be made, thereby enhancing expression.

Gene expression – the detectable effect of a gene, an appearance of an inherited trait.

Genetic map – the position of known genes on a chromosome.

Genetic screening – testing an individual or group of people to see if they carry a particular gene or genes.

Genome – all of the DNA contained in an organism.

Genotype- the genetic make up of an organism.

Growth – the process by which an organism or any of its parts increases in sizes.

Growth delay – occurs when the process through which an organism increases in size is abnormal and behind.


Heart valve - one of the four structures in the heart that control the flow of blood to and from the heart.

Heterozygous – having 2 different alleles of a gene at one locus, one inherited form each parent.

Homozygous – having 2 alleles of a gene that are the same.


Immune system - the system in the body that protects itself from foreign substances, such as bacteria and viruses.

Inherited – passed on to an individual through the parent’s genetic code

Insertion – a piece of genetic material inserted into an existing gene sequence, often causing a mutation.

Interrupted aortic arch – part of the aorta is missing. This can lead to severely reduced blood flow to the lower part of the body.

Introns – a portion of DNA that lies between the exons. It is spliced out in MRNA and does not get translated into protein.



Kidney – one of a pair of organs located on the right and left side of the abdomen. Its function is to filter blood in the body and clear it from poisons. It is also responsible for excreting the end products of the body’s metabolism in the form of urine which is eliminated from the body during urination. It also regulates acid concentration in the body


Linkage – the relationship between 2 or more non- allelic genes on the same chromosome that causes them to be inherited together.

Locus – the position of a gene on a chromosome.


Mitral valve - the valve between the left atrium and left ventricle. Prevents blood from flowing back into the atrium from the ventricle. It consists of two flaps, or cusps.

Monosomy – having only one copy of a particular chromosome instead of the usual 2 copies.

Mutation- any detectable and heritable change in the genetic material.


Newborn – recently born; generally pertaining to the first four weeks of life.



Parathyroid - the gland behind the thyroid gland. It is responsible for calcium regulation as well as secreting a hormone that regulates calcium and phosphorus metabolism.

Pediatrician – a physician who specializes in the care of infants and children.

Pedigree –chart, diagram or list that depicts an individual’s ancestors, used in genetics to analyze patterns of inheritance.

Phenotype – the characteristics of an individual that are produced by the interaction of genotype and environment.

Polymorphism – the simultaneous occurrence in the population of genomes showing allelic variations (e.g. as seen in alleles producing different phenotypes)

Promoter - a region of DNA that RNA polymerase binds to in order to initiate transcription of DNA into RNA.

Protein - chemical substance produced by the DNA. Proteins determine what job a cell will do.

Pulmonary artery - the large artery that receives blood from the right ventricle and carries it to the lungs.

Pulmonary valve - the heart valve between the right ventricle and the pulmonary artery. It consists of three flaps, or cusps.



Recessive – mutation or disorder that is only expressed when a mutant allele it is paired in a homozygous form. It is obscured by the dominant allele in the heterozygous form.

Recurrent infection – an infection in the body that returns after being absent or in remission for a period of time.

RNA (ribonucleic acid) - RNA is very similar to DNA. However, RNA function is different from that of DNA. It is involved in
processing the information from the DNA to make proteins.


Septum - one of the muscular walls dividing the two chambers on the left side of the heart from the two chambers on the right.

Sex chromosome – a chromosome (X or Y) that determines the sex of an individual. Females have two X chromosome and males have an X and Y.

Sex-linked – a genetics disorder that is linked with one of the sex chromosomes

Side effect - any reaction that results from a medication or therapy.

Single gene disorders - hereditary disorders caused by a single gene.

Sporadic- not inherited, occurring occasionally, in irregular instances

Stenosis - the narrowing or constriction of an opening

Structure – the arrangement of the components that make-up a part of the body, e.g. the heart.

Syndrome - a set of characteristics that are seen together more frequently than by chance alone.

Systolic pressure - the pressure of blood inside arteries when the heart contracts. In a blood pressure reading, this is the top number.


Teratogens - any substance that can cause a birth defect.

Trait – a qualitative characteristic. An attribute of phenotype, not genotype.

Translocation - a chromosome alteration involving a change in position of a chromosome piece (or pieces) and the gene sequences it contains.

Tricuspid valve - the heart valve between the right atrium and right ventricle. It resembles the mitral valve, but has three flaps, or cusps.

Trisomy – having an extra chromosome, possessing three copies of a particular chromosome instead of the normal two.


Urinary tract infection – a bacterial infection that affects any part of the urinary tract. This includes the urethra, bladder, and kidneys. Usually treated with antibiotics.


Valve - an opening, covered by membrane flaps, between two chambers of the heart or between a chamber of the heart and a blood vessel.

Vascular - pertaining to the blood vessels.

Vein - any one of a series of vessels that carry blood from various parts of the body back to the heart.

Ventricle - one of the heart's two lower chambers that receive blood from the atria

Velopharyngeal - referring to the soft palate and pharynx region.

Velopharyngeal incompetence - a disorder of the soft palate and pharynx (throat) in which the muscular portion in the soft palate and throat fail to close completely during normal speech.





The following websites are also a good resources for definitions:
Multilingual Glossary of Medical Terms
NHGRI glossary (National Human Genome Research Institute)
Genetic Alliance Glossary


Campbell, N. Biology, 4th ed. The Benjamin/Cummings Publishing Co, Inc. Menlo Park, CA 1987

Lewin, B. Genes, 6th ed. Oxford University Press, Inc. New York, NY. 1997


Last Update 4-15-05