CoachThe genetic information of a cell is the set of instructions, transmitted from a cell to its daughter cells and from parents to offspring, that determines the traits of the organism and the proteins its cells can make. In every living thing it is carried by molecules of DNA (deoxyribonucleic acid), packed with proteins into the chromosomes — in the nucleus of a eukaryotic cell, free in the cytoplasm of a bacterium.
Examples
Example 3.3 (Where the DNA is)
A dye specific for DNA stains the nucleus of a cheek cell and nothing else in the cytoplasm; in a dividing cell it stains the compact chromosomes. A bacterium takes up the dye in a central region without an envelope. In both, the amount of DNA doubles before each division and is halved between the two daughter cells — the behaviour expected of information that must be copied and shared.
Example 3.6 (Chargaff’s rule in numbers)
Human DNA: A 30.9%, T 29.4%, G 19.9%, C 19.8% — AT and GC to within the precision of the measurement, and A+T . E. coli: A 24.7%, T 23.6%, G 26.0%, C 25.7%, A+T . Yeast: A+T . If a DNA sample contains 32% of A, complementarity predicts 32% of T and each of G and C.
Example 3.10 (Numbers)
The human genome — one complete set of chromosomes — carries base pairs and about genes; genes occupy only a few per cent of the sequence. A cell of E. coli carries one circular DNA molecule of base pairs and about 4300 genes. Two unrelated humans differ at roughly one base in a thousand: some three million positions, most of them outside genes and of no consequence, a few of them alleles that change a trait.