Definition of Radiation Hybrid

According to Merriam-Webster Dictionary, "Hybrid means an offspring of two animals or plants of different races, breeds, varieties, species, or genera." The term "radiation hybrid" signifies for a hybridized cell that generally contains tiny fragments of irradiated chromosomes (generally human). These may also be referred to as "radiation reduced hybrids." Medical science has taken the advantage of radiation hybrid technology in localizing human disease genes in the genome.

Radiation Hybrid Mapping

• Radiation hybrid mapping is a genetic engineering process that was originally developed for constructing long-range maps of mammalian chromosomes and discovering the location of genetic markers relative to one another. Radiation hybrid mapping is rooted in a statistical model to measure the distances between deoxyribonucleic acid (DNA) markers and their order on the chromosomes. DNA markers are very short. Cyclic DNA sequences are contained within a genome. Radiation hybrid mapping has proven to be indispensable for localizing human disease genes in the genome. The relative location of these DNA markers can be coalesced into a physical map known as a genetic map.

Steps of Radiation Hybrid Technique

• The first step of the radiation hybrid technique involves amplification and purification of DNA similar to the first step in any sequencing project. Radiation is then employed to split the DNA into smaller segments and these segments are then incorporated into a hybrid cell. The radiation hybrid cell is then cultivated to be grown in large quantities. Polymerase chain reaction (PCR) and linkage analysis are used to resolve the distance between the DNA markers. You can easily check for the presence of various genetic markers. The closer the two genetic markers are to each other, the less is the likelihood to be separated by the DNA-splitting radiation.

Procedure/Technique

• The procedure of radiation hybrid technique involves the usage of two different cell lines that are incapable of survival in a toxic media. However, they contain genes that can resist the toxic media when combined into a single cell (due to production of a toxin resistant enzyme). The cell line under study is irradiated (usually by X-Rays), causing breaks in the DNA. This causes the chromosome to break into several segments that are subsequently fused or integrated with the other cell line, producing a hybrid. Since the hybrid has incorporated genes from both cell lines and can produce the required enzyme, it will survive in the toxic media.

Cultivation

• The hybrid cell that can survive is now cultivated in large quantities. This amplifies the DNA inherited from the irradiated cell line. The resulting sample is then subjected to PCR to amplify two specific genetic markers. By running the PCR products on a gel, it can be verified if that both markers are incorporated in the resulting cell line. The frequencies with which DNA markers are retained in each clone (cultivated sample) can be calculated using statistical methods.

Application

• The generated maps of chromosomes for the multiple species such as humans, rat, mouse and other genomes facilitate the generation of highly detailed and precise maps used to studying multi-factorial diseases. Other applications include determination of chromosome locations of 26 human novel full-length cDNAs (chromosomal DNA).