Glossary

A congenital disorder in which part of the colon lacks nerve cells and therefore is unable to relax. The result is chronic constipation and distention of the abdomen. The disorder affects about one in 5000 U.S. newborns but can be treated with surgery.

The degree to which tissue from one organism will be tolerated by the immune system of another organism.

An antigen that causes the rejection of grafted material from an animal different in genotype from the host animal.

The collection of genes coding for peptides present on the surface of nucleated cells; these peptides are responsible for the differences between genetically non-identical individuals that cause rejection of tissue grafts between such individuals. These peptides were originally called histocompatibility antigens. They are now called histoglobulins, reflecting their structural similarity to immunoglobulins.

Control subjects (followed at some time in the past or for whom data are available through records) who are used for comparison with subjects being treated concurrently. The study is considered historically controlled when the present condition of subjects is compared with their own condition on a prior regimen or treatment.

Documents representing a point-in-time (“snapshot”). These are not updated continuously.

Human Immunodeficiency Virus

Human-Machine Interface

Hazardous Materials Regulations

Hazardous Materials Transportation Act

High Molecular-Weight High Density Polyehtylene

Hydrogenated Nitrile Rubber

The volume of liquid remaining in a vessel or piping system after it has been allowed to drain.

Considering the whole system or process and its interdependencies rather than addressing separate parts in isolation.

A tube of a porous material, having an internal diameter of a fraction of a millimeter, and so its ratio of surface area to internal volume is very large. This has had two types of application. Firstly, hollow fibres can be used as filters. Because they have a huge surface area, they take much longer to clog up than normal filters. Secondly, they are used in the hollow fibre bioreactor, in which cells are kept inside the hollow, porous fibers, and the culture medium is circulated outside the reactor. The fibers let nutrients in and products out (as they are in solution), but do not allow the passage of cells. Hollow fiber bioreactors are very effective for maintaining mammalian cells in culture because they have a very large surface area for the cells to grow on without needing a large reactor to hold them, and because the nutrient reaching the cells can be kept fresh. The reactor also provides an easy way of removing the product that the cells are making: such as monoclonal antibodies. Hollow fiber reactors are less use when the cells themselves have to grow, because it is hard to get at the inside of the fiber to remove surplus cells.

A birth defect where the forebrain does not separate properly into two halves during early fetal life. The disorder results in mild to severe brain malformation and is sometimes fatal. It may be caused by environmental or genetic factors. Holoprosencephaly affects between 1 in 5,000 and 1 in 10,000 live births.

A DNA sequence found in several genes that are involved in the specification of organs in different body parts in animals; they are characteristic of genes that influence segmentation in animals. The homeobox corresponds to an amino acid sequence in the polypeptide encoded by these genes; this sequence is called the homeodomain.

A member of a chromosome pair in diploid organisms or a gene that has the same origin and functions in two or more species.

From the same source, or having the same evolutionary function or structure.

Chromosomes that occur in pairs and are generally similar in size and shape: one comes from the male parent and the other from the female. Such chromosomes contain the same linear array of genes.

Genes with similar structures and functions.

The exchange of pieces of DNA during the formation of eggs and sperm. Recombination allows the chromosomes to shuffle their genetic material, increasing the potential of genetic diversity. Homologous recombination is also known as crossing over.

The degree of identity between individuals, or characters. The degree of identity between the nucleotide sequences of two nucleic acid molecules or the amino acid sequences of two protein molecules. Although sequence determination is the ultimate test of homology, useful estimates can be provided by either DNA-DNA or DNA-RNA hybridization.