"Until about 1925, geneticists were mainly concerned with the demonstration, confirmation, modification and extension of Mendel's laws, and with their bearing on the problem of evolution. The genes were thought of as discrete units, and interest was focussed mainly on their identification and localization on the chromosomes, and the way in which they were combined, segregated and transmitted through the germ cells. More recently the attention of geneticists has turned more and more from what Goldschmidt (1938) terms the 'static' towards the 'dynamic' aspects of genetic research; namely, the causal relationships existing between the genotype and the phenotype. It is realized that, in most cases at least, the primary action of the gene is connected with its phenotypic effect by a long series of developmental reactions, and that each series affects and is affected by many similar series stemming from other genes, so that the pattern of development is determined by an intricately branched and interlacing network of gene-initiated reaction chains. Two fundamental questions must be answered: (1) what is the nature of the gene, and (2) what is its mode of action? [...]" --

"The term "crossing-over" is used to denote the exchange of pieces or segments between homologous chromosomes. The mechanism by which this exchange is brought about has constituted one of the major fields of genetical and cytological research for many years. The early work on crossing over was done by genetical methods which provided the means of analysis of the organization of linkage-groups--an analysis which was fundamental to the chromosome theory of heredity. Among the important discoveries resulting from the study of crossing-over were: (1) the linear arrangement of the genes (Sturtevant, 1913a), (2) the occurrence of interference between the crossing-over of nearby segments (Muller, 1916), and (3) proof that crossing-over occurs in the "4-strand stage" (Bridges, 1916; Bridges and Anderson, 1925; etc.). It was not until 1931, however, that Stern (1931), working with Drosophila, and Creighton and McClintock (1931) and Brink and Cooper (1935), working with Zea mays, demonstrated that crossing-over actually is an interchange of parts between homologous chromosome. [...] The present study was undertaken to determine whether there is also a relationship between the effect on crossing-over in a non-homologous chromosome and the length and position of the inversion by which it is affected. [...]" --

Due to the recent advances in genetic knowledge, your family history has become far more crucial to understanding your health than simply for tracing your ancestry. Author Clarke Fraser, Canada's first medical geneticist, uses his extensive knowledge, wisdom, and wit to show the relationship between your genealogy and genetic diseases. Your Genealogy Affects Your Health: Know Your Family Tree itemize the genetic and environmental factors that increase or reduce the risks for common familial disorders. Most genealogists do not record the important facts, like what diseases people had. Fraser tells how becoming familiar with your family's history of disease shows what steps you can take to reduce your risk of getting a close relative's particular disorder. He offers timely information on topics such as: how genes work how to draw a pedigree how DNA is used to trace your ancestry how normal traits such as handedness, baldness and intelligence run in families how common disorders such as cancer, obesity, coronary disease, alcoholism and schizophrenia run in families Invest in your future health by researching your past with the help of Your Genealogy Affects your Health