Trends in genetics--before the molecular era.

Molecular techniques and biochemical questions came to dominate genetic research during the later half of the 1900th century. This does not mean that earlier achievements have lost their importance. In this review the trends in classic genetics are followed from the beginning in 1900 until the molecular aspects took over, and it is shown how they form the basis for many trains of thought in present day genetics.

Old and new ideas about genes and behaviour.

Genetic factors have long been recognized as contributors to variantion in behaviour both within the normal span and as mental diseases. The first attempts to make behaviour the subject of scientific genetic studies used likeness between twins and other relatives to confirm heredity. Later heritability has been used as a quantitative estimate of the genetic part of the variance.

Genealogy and gene trees.

Heredity can be followed in persons or in genes. Persons can be identified only a few generations back, but simplified models indicate that universal ancestors to all now living persons have occurred in the past. Genetic variability can be characterized as variants of DNA sequences.

Fluctuating asymmetry--indicator of what?

In a population the optimal phenotype is promoted by buffering mechanisms that keep inter- and intra-individual variation low. A link exists between canalization, that controls phenotypic variation, and developmental stability, mostly measured as fluctuating asymmetry of bilateral traits (FA). Both types of variation are associated with the functional importance of a trait, and both are increased by stress of various kinds.

Review. The genotype-phenotype link.

The basic knowledge which has opened for the new discipline of functional genomics stems from one hundred years of debates and experimentation among devoted geneticists, who tried to understand the processing of gene expression into phenotypic design without the molecular tools that are now available. Here I recapitulate some old and some newer results from this research, which illustrate the ways in which changes in genetic variation can be induced, how it can be kept latent or, when needed, be expressed in the phenotype.