The inheritance of acquired epigenetic variations.

There is evidence that the functional history of a gene in one generation can influence its expression in the next. In somatic cells, changes in gene activity are frequently associated with changes in the pattern of methylation of the cytosines in DNA; these methylation patterns are stably inherited. Recent work suggests that information about patterns of methylation and other epigenetic states can also be transmitted from parents to offspring.

Précis of Evolution in Four Dimensions.

In his theory of evolution, Darwin recognized that the conditions of life play a role in the generation of hereditary variations, as well as in their selection. However, as evolutionary theory was developed further, heredity became identified with genetics, and variation was seen in terms of combinations of randomly generated gene mutations. We argue that this view is now changing, because it is clear that a notion of hereditary variation that is based solely on randomly varying genes that are unaffected by developmental conditions is an inadequate basis for evolutionary theories.

The evolution of information in the major transitions.

Maynard Smith and Szathmáry's analysis of the major transitions in evolution was based on changes in the way information is stored, transmitted and interpreted. With the exception of the transition to human linguistic societies, their discussion centred on changes in DNA and the genetic system. We argue that information transmitted by non-genetic means has played a key role in the major transitions, and that new and modified ways of transmitting non-DNA information resulted from them.

The changing concept of epigenetics.

We discuss the changing use of epigenetics, a term coined by Conrad Waddington in the 1940s, and how the epigenetic approach to development differs from the genetic approach. Originally, epigenetics referred to the study of the way genes and their products bring the phenotype into being. Today, it is primarily concerned with the mechanisms through which cells become committed to a particular form or function and through which that functional or structural state is then transmitted in cell lineages.

The DNA content of polytene nuclei in midgut and Malpighian tubule cells of adultDrosophila melanogaster.

The amounts of DNA in midgut and Malpighian tubule cells of adult maleDrosophila melanogaster have been determined by Feulgen-DNA cytophotometry. The DNA values fall into discrete classes reflecting different levels of polyteny. The maximum level is 64C in the midgut, 256C in Malpighian tubules, and the modal values are 32C and 128C respectively.