Ch 5Molecular Basis of Inheritance — Class 12 Biology, concept-first.

Every cell that has ever existed arose from a pre-existing cell, and every offspring resembles its parents far more closely than it resembles an unrelated member of the same species.

The first experimental clue to the identity of the genetic material came not from any deliberate search for it, but from a study of pneumonia in mice carried out by the British medical officer Frederi…

Griffith's 1928 experiment had proved that a "transforming principle" existed and could convert harmless R-strain bacteria into virulent S-strain bacteria, but it left the chemical identity of that su…

Even after Avery, MacLeod and McCarty's 1944 biochemical proof, a substantial part of the scientific community remained unconvinced that DNA, rather than protein, was the genetic material — the doubt…

Once the three landmark experiments of Griffith, Avery-MacLeod-McCarty, and Hershey-Chase had jointly established that DNA is the molecule of heredity, the next essential question was structural: what…

Ribonucleic acid, or RNA, is chemically very similar to DNA but differs from it in three important structural respects.

A single human cell contains roughly two metres of DNA in total, yet this enormous length must somehow be folded and compacted to fit inside a nucleus only a few micrometres across — a packaging probl…

Every time a cell divides, its entire DNA content must first be duplicated, so that each of the two resulting daughter cells receives a complete, identical copy of the genetic material — this copying…

DNA replication is a highly coordinated process carried out by a large team of specific enzymes and proteins working together at a structure called the replication fork — the Y-shaped point where the…

Having established that DNA is the genetic material, that it is structured as a double helix, and that it replicates semiconservatively to be faithfully passed from one generation of cells to the next…

Transcription is the process by which the genetic information encoded in a specific segment of DNA (a gene) is copied into a complementary strand of RNA.

In bacteria, because there is no nuclear membrane separating the DNA from the ribosomes, the mRNA transcript produced by RNA polymerase is generally translated at the ribosome directly and immediately…

Once a gene's information has been transcribed into mRNA, the cell faces a further, purely informational problem: mRNA is written in an alphabet of just four different nucleotide bases, while a protei…

Translation is the process by which the coded sequence of codons carried by an mRNA molecule is used to direct the synthesis of a specific polypeptide (protein) chain, with each codon specifying one p…

A cell contains many more genes than it needs to have switched on at any given moment, and expressing every gene constantly, regardless of whether its product is actually needed, would be a wasteful u…

The Human Genome Project (HGP) was an ambitious, internationally coordinated scientific effort, formally launched in 1990 and largely completed by 2003, with the overarching goal of determining the co…

DNA fingerprinting is a molecular biology technique that identifies and compares specific, highly variable regions of an individual's DNA, producing a distinctive banding pattern unique (or very nearl…

This chapter traced the complete molecular story of heredity, from the search for the identity of the genetic material to its structure, its copying, its expression, its regulation, and its most conse…

Sample papers and previous-year board questions for this subject.