The Watson-Crick model of DNA has been the basis for further work on DNA replication, mutation and recombination. Much evidence exists to establish the validity of this model. Nevertheless, the model has been scrutinized by other workers, and from time to time other models have been suggested by Wu (1970), Arnott (1968), Wang (1979) and a few others. Wang's model [...]
The following point highlight the five main types of structural variation in chromosomes. The types are: 1. Deletion or Deficiency 2. Duplications 3. Translocations 4. Inversions 5. B-Chromosomes. Type # 1. Deletion or Deficiency: A deficiency means deletion of a small portion of a chromosome resulting in loss of one or more genes. A deficiency originates from breakage occurring at [...]
The work of J. Cairns demonstrated DNA replication in bacteria in an elegant way. He used high resolution autoradiography for observing the distribution of radioactive label in the "chromosomes" of dividing E. coli cells. The bacterial cells were grown on a medium containing tritiated thymidine. The labelled DNA was extracted from the cells and spread on EM grids. A very [...]