The Molecular Basis Of Inheritance

Answer (a) m-RNA

Genetic or DNA fingerprinting, DNA testing or DNA profiling is the technique used to distinguish between individuals of the same species using only samples of their DNA. It was invented by Sir Alec . Jeffreys. Variable Number of Tandem Repeat (VNTR) polymorphism is the basis of DNA fingerprinting which are short nucleotide repeats. The location and repetition in VNTR is so unique that no two individuals are alike. During DNA fingerprinting special DNA probes (single stranded labelled DNA rands) which with known sequences of probes complementary to these on VNTRs are used which bind to these VNTRs and make . them radiolabelled and thus observable. DNA fingerprinting may also use RFLP. DNA of each organism has specific sequences calle restriction fragments that can be cleaved by restriction endonuclease enzymes to produce fragments of different lengths. Occurrence of different lengths of cleaved DNA sequences is referred to as restriction fragment length polymorphism (RFLP).

Eukaryotes have three RNA polymerases. RNA polymerase I is located in the nucleolus and transcribes for rRNAs. RNA polymerase II is localized to the nucleo- .plasm and used for hnRNA, mRNA. RNA� polymerase Ill, is localized to the nucleus, possibly the nucleolar-nucleoplasm interface and transcribes for tRNA, 5srRNA and snRNAs. Prokaryotes have only one RNA polymerase which synthesizes all types of RNAs

Temin and Baltimore (1970) reported that double stranded RNA of Rous Sarcoma Virus (RSV) operates a central dogma reverse (inverse flow of information). RNA of these viruses first synthesises DNA through reverse transcription or teminism. DNA then transfers information to RNA which takes part in translation of coded information to form polypeptide. The mechanism is characteristic of retroviruses, e.g., HIV. Reverse transcription is aided by the enzyme known as reverse transcriptase (RNA dependent DNA polymerase) enzyme.

In eukaryotes, the termination of polypeptide chain during translation is brought about by the termination codons. These are UAG, UAA and UGA and these are called as amber, ochre and opal respectively. These codons are also called as nonsense codons as they do not code for any amino acid. AUG is the initiation codon. It codes for (methionine) amino acid.

Transduction, discovered by Zinder and Lederberg in 1952, in Salmonella hjphimurium is a method of genetic recombination in which genetic material is transferred from one bacterium (the donor) to another bacterium (the recipient) by a bacterial virus called a bacteriophage.

A transcription unit is a segment of DNA that takes part in transcription. It has three components: (i) a promoter (ii) a structural gene and (iii) a terminator. Besides a promoter, eukaryotes also ? require an enhancer. Promoter is located upstream of structural gene (at 5' end of coding strand). Terminator region is present downstream at ?3 end. Transcription factors attach at promoter region.