[...]... hill-climbing, in which the best phenotype is reached by a series of steps, each step leading to a type that is fitter than the previous one (the precise meaning of `fit' is discussed in Chapter 3) Applied to the vitro in experiment just described, this concept of hill-climbing implies the following The process started with a short random sequence A, and ended with a unique sequence Z that is replicated... started with a short random sequence A, and ended with a unique sequence Z that is replicated particularly rapidly For this to happen, there must be a series of intermediates, A-B-C- .-M-N- .-Z, such that: 1 Each stepjor example, M-Nfan arise by a single mutation}hat is, a base substitution, deletion, or duplication 2 Each step increases replication rate There could be some debate about whether a... `heredity': that is, like begets like The essential feature of heredity is illustrated in Fig 1.1 Notice that heredity can be defined only for entities that both multiply and vary We do not think of a rock, which is the same today as it was yesterday, as having heredity, because it does not multiply But multiplication and variation are not sufficient Fire multiplies, provided that fuel is supplied,... that will replicate RNA RNA molecules are added as a seed (S) to the first tube After 30 min, a drop of solution is taken from the first tube, and added to the second (T); after a further 30 min, a drop is taken from the second tube, and added to the third, and so on works well in vitro, and will replicate almost any RNA molecule in a test-tube, if it is provided with the four necessary monomers from which... transmitted to new DNA molecules in the process of replication, and which specifies the amino-acid sequence of proteins in the process of translation It is important to be clear about what is being asserted by the central dogma It is not true that DNA can replicate without proteins: enzymes are needed Further, changes in enzymes can alter the way in which a particular DNA sequence is translated What... no long-term evolutionary effects The rest of this book is based on the assumption that this neo-Darwinist picture is correct But first, I review some contexts in which the assumptions are dubious, or actually false 1 Cell differentiation.The cells of higher organisms are differentiatedjor example, fibroblasts, epithelial cells, leucocytes, and so on The differences between these cells are hereditary,... enabling a parent plant to produce seedlings adapted to a changed environment Until we know more of the molecular mechanisms involved, it is hard to decide how common processes of this kind may prove to be However, if the morphological change is indeed adaptive, the genetic system responsible for the gene amplification and its transmission must itself have evolved by natural selection There remains... repeatedly lead to the same end-point can be taken as evidence that, in this case, the three necessary conditions do hold However, it is worth noticing that the end-pointjor example, the molecule of Fig 1.3ray not be, as implied above, the uniquely best sequence Thus it may be that, starting from A, there is an uphill path to Z, but that there is some other molecule, say OPT, which is replicated even... continue indefinitely What is needed if this is to be so? This question is harder than it looks: it will be discussed briefly in the last chapter A more immediate limitation lies in the absence of a clear distinction between phenotype and genotype, and of a process of development In a sense, the genotype of an RNA molecule is its base sequence, and its phenotype is its three-dimensional structure The analogue... that the universe is expanding by saying that it has an inherent tendency to get bigger The Lamarckian theory of the inheritance of acquired characters was A explicitly rejected by August Weismann (183 4-1 914) He claimed (Fig 1.4 ) that, starting from the fertilized egg, there are two independent processes of cell division, one leading to the body or `soma', and the other}he `germ line'qeading to the . is doing what it is intended to do. Page ix Background Knowledge I have assumed some knowledge of genetics, mathematics, and statistics, as follows. Genetics Mendelian genetics, the chromosome. chapters, I have suggested a few computer projects. All these (with one exception that is indicated) can be carried out in BASIC on a micro-computer. I have used many of them as final-year assessment. associated companies in Berlin Ibadan Oxford is a trade mark of Oxford University Press Published in the United States by Oxford University Press Inc., New York John Maynard Smith, 1998, reprinted