Genetic marker		a gene located on an Y chromosome.
Down syndrome		the counseling of individuals with established or potential genetic problems, concerned with inheritance patterns and risks to future offspring.
Sex influenced trait		a cell that's constantly mutating and changing.
Germ cell mutation		a gene that under certain conditions causes the death of an organism.
Genetic counseling		a federally funded U.S. scientific project to identify both the genes and the entire sequence of DNA base pairs that make up the human genome.
Polygenic trait		a pathological condition caused by an absent or defective gene or by a chromosomal aberration. Also called hereditary disease, inherited disorder.
Recombinant DNA		a measure of distance between two linked genes corresponding to a recombination frequency of one percent.
Y linked gene		an individual possessing an unexpressed, recessive trait.
Monosomy		an ancestral line; line of descent; lineage; ancestry.
Chromosome map		of or relating to an inheritable character that is controlled by several genes at once; of or related to or determined by polygenes.
Carrier		in genetics, a diagram showing the relative positions of the chromosome genes
Lethal mutation		a type of chromosomal aberration in which a segment of the chromosome is removed or lost.
Nondisjunction		an association between genes in sex chromosomes such that the characteristics determined by these genes appear more frequently in one sex than in the other.
Amniocentesis		a mutation in a DNA chain that occurs when the number of nucleotides inserted or deleted is not a multiple of three
Sex linkage		a change in a single base in a nucleotide sequence
Genetic engineering		a type of chromosomal aberration in which the position of a segment of the chromosome is changed in such a way that the linear order of the genes is reversed.
Deletion		a group of genes in a chromosome that tends to be inherited as a unit.
Linkage group		a chromosomal landmark or allele that allows for the tracing of a specific region of DNA, as in the study of recombination.
Genetic disorder		a surgical procedure for obtaining a sample of amniotic fluid from the amniotic sac in the uterus of a pregnant woman by inserting a hollow needle through the abdominal wall, used in diagnosing certain genetic defects or possible obstetric complications.
Pedigree		the failure of chromosomes to separate and segregate into daughter cells at division.
Frame shift mutation		the development and application of scientific methods, procedures, and technologies that permit direct manipulation of genetic material in order to alter the hereditary traits of a cell, organism, or population.
Inversion		a genetic disorder, associated with the presence of an extra chromosome 21, characterized by mild to severe mental retardation, weak muscle tone, a low nasal bridge, and epicanthic folds at the eyelids.
Point mutation		A chromosome having no homologue, especially an unpaired X-chromosome.
Map unit		DNA in which one or more segments or genes have been inserted, either naturally or by laboratory manipulation, from a different molecule or from another part of the same molecule, resulting in a new genetic combination.
Human genome project		Traits that appear more of time in one sex than in the other.