One is unequal crossing over, in which recombination happens between different positions on chromosomes that are misaligned during meiosis. 

Another is replication slippage, in which the DNA polymerase loses its place and copies a segment of chromosome twice.

TLS Online TPP Program

#Id: 4625

#Unit 13. Methods in Biology

The interaction between antibody and a particulate antigen results in visible clumping called agglutination. Antibodies that produce such reactions are called agglutinins.

TLS Online TPP Program

#Id: 4626

#Unit 13. Methods in Biology

Agglutination reactions are similar in principle to precipitation reactions they depend on the crosslinking of polyvalent antigens. Just as an excess of antibody inhibits precipitation reactions, such excess can also inhibit agglutination reactions; this inhibition is called the prozone effect.

TLS Online TPP Program

#Id: 4627

#Unit 13. Methods in Biology

A modification of the agglutination reaction, called agglutination inhibition, provides a highly sensitive assay for small quantities of an antigen. For example, one of the early types of home pregnancy test kits included latex particles coated with human chorionic gonadotropin (HCG) and antibody to HCG.

TLS Online TPP Program

#Id: 4628

#Unit 13. Methods in Biology

Enzyme-linked immunosorbent assay, commonly known as ELISA (or EIA), is similar in principle to RIA but depends on an enzyme rather than a radioactive label. 

TLS Online TPP Program

#Id: 4629

#Unit 13. Methods in Biology

A number of enzymes have been employed for ELISA, including alkaline phosphatase, horseradish peroxidase, and -galactosidase. These assays approach the sensitivity of RIAs and have the advantage of being safer and less costly.

TLS Online TPP Program

#Id: 4630

#Unit 13. Methods in Biology

 Antigen can be detected or measured by a sandwich ELISA .In this technique, the antibody (rather than the antigen) is immobilized on a microtiter well. 
A sample containing antigen is added and allowed to react with the immobilized antibody. After the well is washed, a second enzyme- linked antibody specific for a different epitope on the antigen is added and allowed to react with the bound antigen
After any free second antibody is removed by washing, substrate is added, and the colored reaction product is measured.