- Definitions

Allele - One of the variant forms of a gene at a particular locus, or location, on a chromosome. Different alleles produce variation in inherited characteristics such as hair color or blood type. In an individual, one form of the allele (the dominant one) may be expressed more than another form (the recessive one).

Autosome - Any chromosome other than a sex chromosome. Humans have 22 pairs of autosomes.

Cancer - Diseases in which abnormal cells divide and grow unchecked. Cancer can spread from its original site to other parts of the body.

Centrioles - Pairs of cylindrical organelles located at the poles of the spindle in eukaryotic cells. They function in the organization/development of the spindle microtubles.

Centromere - The region where sister chromatids of a chromosome are joined and the spindle fibers attach.

Chromatids - One of the two identical DNA helices that comprise a metaphasic chromosome. The two chromatids result from the replication of the DNA during the S stage of the Cell Cycle.

Cytokinesis - Cytoplasmic division, begins during the last stage of mitosis (Telophase). The actual process of a cell dividing.

DNA Replication - DNA replicates by "unzipping" along the two strands, breaking the hydrogen bonds which link the pairs of nucleotides. Each half then serves as a template for nucleotides available in the cell which are joined together by DNA polymerase. The nucleotides are guanine, cytosine, adenine, thymine.

Gene - The functional and physical unit of heredity passed from parent to offspring. Genes are pieces of DNA, and most genes contain the information for making a specific protein

Genetic testing - the use of specific assays to determine the genetic status of individuals already suspected to be at high risk for a particular inherited condition. The terms genetic test, genetic assay, and genetic analysis are used interchangeably to mean the actual laboratory examination of samples.

Genotype - The allelic composition of an individual. Usually a literal listing of the alleles.

Heterozygous - Possessing two different forms of a particular gene, one inherited from each parent

Histones - Basic proteins that are found associated with DNA in the chromatin fiber.

Homologues - Chromosomes possessing the same types, or kinds, of genes. In Diploid organisms they come in pairs.

Homozygous - Possessing two identical forms of a particular gene, one inherited from each parent.

Kinetochore - The point of attachment for the spindle fibers onthe centromere of chromosomes during mitosis or meiosis.

Nucleus - The nucleus is the organelle of a cell that contains the chromosomes. The nucleus contains a cell's DNA.

Nucleolus - A spherical body located within the nucleus that contains primarily RNA and protein; in a nucleus there may be more than one nucleolus.

Microtubules - The microtubules are straight and undefinite in length. They contain an outside diameter of 200 to 270 A, and a dense wall of 50 to 70 A in thickness. Groups of such microtubules form the spindle apparatus of dividing cells and the marginal band of nucleated erythrocytes.

Microfilaments - A thin filaments about 60 A in thickness composed of actin. The contractile ring is composed of microfilaments.

Phenotype - The manifestation of the Genotype. It can be the individual's appearance or biochemical constitution.

Spindle fibers - Bundles of microtubules that form the visible fibers of mitotic or meiotic spindle apparatus.

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