dnatools

(or words that I have collected that I think are useful in the language of DNA/Genetics)

AFP (a-fetoprotein): A protein made by the fetus, but present in very small amounts in adults. Increased amounts are found in amniotic fluid of fetuses with anencephaly or spina bifida.

Amino acids: Small chemical building blocks that join together to form proteins. Three-letter codes inDNA specify the amino acids in proteins.

Amnion: The thin tissue of fetal origin that lines the fluidfilled cavity containing the fetus within the uterus.

Anencephaly: One of a series of defects in which the tube of tissue destined to form the brain and spinal cord fails to close, in this case resulting in absence of brain, skull cap, and scalp.

Autosome: A nonsex chromosome; one of those numbered 1-22, rather than the X or Y sex chromosomes.

Carrier: A person who has one normal and one abnormal recessive gene at a locus; a heterozygote.

Chorionic villus sampling (CVS): Obtaining fetal tissue (chorion frondosum) sestined to develop into the placenta, performed at 9-11 weeks using a thin plastic tube inserted through the birth canal.

Chromatid: Each of two duplicate strands of a chromosome seen during cell division and destined to separate into each daughter cell.

Chromosome: Rod-shaped dark-staining structures visible during cell division containing genes encoded in DNA lined up like beads on a string.

Compound heterozygote: Having two different genes at a locus, both genes being different from each other and different from the normal, e.g., Hemoglobin SC.

Congential: Present at birth, not necessarily inherited.

Consanguineous: Related by having a common ancestor.

Crossing Over: The normal process of exchange of parts of the two chromosomes of a homologous pair during meiosis.

Cytogenetics: Microscopic study of chromosomes and how changes affect individulas.

DNA: Deoxyribonucleic acid, the chemical structure of genes within chromosomes.

DNA fingerprints: Fragments of DNA separated intoa pattern that is unique to an individual.

Dominant: A trait requiring only one gene for expression in a person.

Electrophoresis: Separation of molecules using an electric current.

Gene: Smallest unit of inheritance consisting of a segment of DNA coding for a chain of amino acids (a polypeptide or protein.)

Genetic code: Sequence of three bases (adenine, thymine, guanine, or cytosine) in DNA, specifying the amino acids in a protein and often written as a chain of letters, e.g., AATCGGCTT, and so forth.

Genetic counseling: Discussion of information with a person(s) about risks for, consequences of, and management of genetic disorders.

Germ cells: Gametes. Sperm in males, ova in females, each containing a single set of 23 chromosomes.

Hardy-Weinberg equation: p squared + 2pq + q squared; where p and q are ganes at a focus, then the three terms are the frequencies of homozygous normal (pp), carriers (2pq), and homozygous affected (qq). The carrier frequency can be calculated from the frequency of affected.

Hemoglobin: Oxygen-carrying proteins of red blood cells.

Heterozygous: Having two different genes at the corresponding loci on the two chromosomes of a pair.

Histocompatibility: Inherited differences in tissues that can cause transplanted organs to be rejected.

Homologous: Chromosomes or parts of chromosomes having the same genetic loci.

Imprinting: A reversible change in gene action rather than a change in the DNA code itself that may be transmitted from one generation to another.

Inherited: Transmitted from parent to child in the genes.

Inversion: A part of a chromosome with reversed gene order.

Karyotype: Picture of chromosomes from a single cell arranged in order from largest to smallest.

Klinefelter syndrome: A male with one Y and two or more X chromosomes, most often having 47 total chromosomes.

Linkage: Genes at loci so close on the same chromosome that they are not usually separated by the process of crossing over during germ cell formation.

Locus: The position of a specific gene on a chromosome.

Meiosis: One duplication of chromosomes followed by two cell divisions producing a germ cell with a single set of chromosomes.

Mithochondria: Small bodies in the cell cytoplasm that provide energy.

Mitosis: Process of cell division in somatic cells (cells other than germ cells) yielding two new cells each having an identical set of 46 chromosomes.

Mosaic: An idividual with two or more cell types difering in gene or chromosome content, e.g., 45, X / 46, XX in a person with Turner syndrome having only one X chromosome on some cells and two in other cells.

Multifactorial: Caused by added effects of multiple genes plus one or more environmetal factors.

Mutation: Change of an existing gene to a new gene by altered DNA coding.

Nondisjunction: Failure of the two chromatids of a chromosome to separate during cell division so that both go to the same daughter cell.

Oncogene: A normal animal gene that on transfer to a virus can have increased activity in cancers when reintroduced into animals.

Ovum: a female germ cell, or egg, containing a single (haploid) set of 23 chromosomes.

PCR: Polymerase chain reaction; a method for gene duplication in the laboratory providing a sensative, rapid method for study of genes for which the DNA code, or part of the code, is known.

Pedigree: Diagram of family relationships showing persons affected by a genetic disorder.

Polygenic: Caused by additive effects of multiple genes at different loci.

Polmorphism: Two or more different genes for a function occurring at a rate of one in a hundred or greater for the least common gene.

Polyploidy: Multiple sets of the number of chromosomes in germs cells (23) beyond the normal 46 for tissue other than germ cells, e.g., triploid = 69.

Propositus: Proband; person through whom the family is discovered.

Recessive: A trait expressed only when both genes are abnormal, either the same (homozygous) or two different genes, both abnormal (compound heterozygous).

Restriction endonuclease: An enzyme that cuts DNA only at sites for a specific short sequence of the DNA code.

RFLP: Restriction fragment length polymorphism; inherited variation in size of pieces of DNA detected after cutting with site- specific enzymes.

Sonography: Pictures made using echoes from very high frequency sound.

Sperm: Spermatozoa; male germ cells containg a single (haploid) set of 23 chromosomes.

Spina bifida: Open spine, one form of major central nervous system defect (see anencephaly.)

Syndrome: Agroup of features occurring together in a pattern sufficient to define a diagnosis, e.g., Down syndrome owing to Trisomy 21.

Teratogen: An agent thatcan cause birth defects by interfering withdevelopment during pregnancy to produce permanent change in an embryo or fetus.

Translocation: Joining of part of a chromosome to another.

Trinucleotide repeats: Long chains of three bases, e.g., CAG, CAG, CAG, . . .and so forth, in DNA.

Trisomy: Having three chromosomes instead of a pair.

Turner syndrome: A female with abnormal ovaries, short stature, and often other congenital abnormalities most oftencaused by having only one normal X chromsome, but sometimes other chromosome variations.

Twins: Two individuals resulting from a single pregnancy; fraternal (dizgotic) if from different fertilized eggs, identical (monozygotic) if derived from splitting of a single fertilized egg into two embryos.

X linked: See linked; genes on the X chromosome unpaired by the much shorter Y chromosome. One abnormal gene produces disease in males, e.g., hemophilia.