Ch 4Molecular Basis of Inheritance — Class 12 Biology, concept-first.

Nucleic acids were identified well before their genetic role was understood. In 1869, the Swiss biochemist Friedrich Miescher isolated a phosphorus-rich, acidic substance from the nuclei of white bloo…

By the early 1900s geneticists knew that genes control inherited traits, that genes sit on chromosomes, and that chromosomes are made mainly of DNA and protein -- but most researchers initially assume…

The DNA double helix in a typical mammalian cell is roughly 2.2 metres long, yet it must fit inside a nucleus only about a micrometre (10^-6 m) across; the 2.2 m figure is simply the total number of b…

Packaging in Prokaryotes: Bacteria such as E. coli have no nuclear membrane or nucleolus; instead their DNA exists as a small, circular, highly folded structure called the nucleoid. In E.

Packaging in Eukaryotes: Eukaryotic cells have a well-organised nucleus with a nuclear membrane, a nucleolus, and thread-like chromosomes in which DNA is associated with histone and non-histone protei…

Heterochromatin and Euchromatin :

The DNA molecule regulates and controls all the activities of the cell; because of its unique structure it controls the synthesis of the cell's other molecules, and when the cell reproduces the DNA mu…

Proteins act as structural components, enzymes and hormones, and cells must continually synthesise new ones.

A. Transcription: During transcription, only one strand of a gene's DNA -- the template (antisense) strand -- is copied into RNA, a reaction catalysed by the enzyme RNA polymerase.

Genetic Code: DNA is the master molecule of the cell: it initiates, guides, regulates and controls protein synthesis, so it must carry the information for the synthesis of proteins within itself.

t-RNA - the adapter molecule: Scientists reasoned that there must be a mechanism by which tRNA reads the codon and at the same time binds the amino acid, since an amino acid has no special capacity to…

Genes of a cell are expressed to perform different functions. For example E. coli synthesises the enzyme beta-galactosidase, which hydrolyses lactose into galactose and glucose:

The operon is a transcriptional control mechanism of gene regulation. Francois Jacob and Jacques Monod (1961) explained that metabolic pathways are regulated as a unit.

The genome (a term introduced by H. Winkler in 1920) is the total genetic constitution of an organism -- a complete copy of its genetic information (DNA), or equivalently one full haploid set of its c…

The Human Genome Project (HGP) was a multinational effort, initiated in 1990 under the international administration of the Human Genome Organization (HUGO) and coordinated by the US Department of Ener…

Genes present on chromosomes determine the characters of an organism and their inheritance. Because of the recombination of paternal and maternal genes we differ from our parents, and differences also…

Q.1 of the textbook exercise (p92): ten multiple-choice questions on the chapter.

Q.2 of the textbook exercise (p92): nine very-short-answer questions.

Q.3 of the textbook exercise (p92): four short-answer questions (printed as an unnumbered list; numbered 1 to 4 here in printed order).

Q.4 of the textbook exercise (pp92-93): the book's second 'Short Answer Questions' group - five questions, two of them on labelled diagrams and one a match-the-columns.

Q.5 of the textbook exercise (p93): six long-answer questions; question 5 has four statements (i-iv) to justify or correct, and question 6 is a table to complete.

The textbook's end-of-chapter Project (p93): collect information about the B and Z forms of DNA, sketch them and write their differences. A guided approach is given.

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