Q.Name the two purine and three pyrimidine nitrogenous bases found across DNA and RNA.

The cistron is the functional unit of a gene - the stretch of DNA that codes for one complete polypeptide chain.

Benzer's model breaks the gene down into three functional units based on what change in the DNA they measure:

• CISTRON - the unit of FUNCTION: the smallest segment of DNA that must be intact to produce one functional polypeptide. This is the working definition of "one gene" in the classical sense.
• MUTON - the unit of MUTATION: the smallest segment of DNA whose alteration (even a single base change) can produce a mutant phenotype - as small as a single nucleotide pair.
• RECON - the unit of RECOMBINATION: the smallest segment of DNA that can be exchanged/recombined between homologous chromosomes without breaking apart - also as small as a single base pair. …

Among the options, DNA viruses are the exception where RNA is not the genetic material.

Every cellular organism (bacteria, algae and all higher organisms) uses DNA as hereditary material but always synthesises and uses RNA (mRNA, tRNA, rRNA) for gene expression. Certain viruses such as TMV (Tobacco Mosaic Virus) use RNA itself as their genome. DNA viruses, however, carry DNA as thei …