Question

A probe is used in which stage of genetic engineering?

Answer 1

A probe is used in screening stage.

Probes are always single-stranded, and can be made of DNA or RNA. If a probe is added to a mixture of different pieces of DNA (e.g. restriction fragments) it will anneal (base pair) with any lengths of DNA containing the complementary sequence. These fragments will now be labelled and will stand out from the rest of the DNA. DNA probes have many uses in genetic engineering:

To identify restriction fragments containing a particular gene out of the thousands of restriction fragments formed from a genomic library. This use is described in shotguning below. To identify the short DNA sequences used in DNA fingerprinting. To identify genes from one species that are similar to those of another species. Most genes are remarkably similar in sequence from one species to another, so for example a gene probe for a mouse gene will probably anneal with the same gene from a human. This has aided the identification of human genes. To identify genetic defects. DNA probes have been prepared that match the sequences of many human genetic disease genes such as muscular dystrophy, and cystic fibrosis. Hundreds of these probes can be stuck to a glass slide in a grid pattern, forming a DNA microarray (or DNA chip). A sample of human DNA is added to the array and any sequences that match any of the various probes will stick to the array and be labelled. This allows rapid testing for a large number of genetic defects at a time