Methods of setting automatic digital computers to simulate the algebraic aspects of reproduction, segregation, and selection are discussed. The application of these methods to the problem of the importance of linkage in multifactorial inheritance is illustrated by results from the SILLIAC.

No abstract

Rates of progress of single populations under selection pressure have been simulated by an automatic electronic computer. Varying intensities of selection and tightness of linkage are compared, showing that linkage produces no qualitative effect on the rates of advance at values greater than 0�005, i.e. 0�5 per cent. recombination.

SummarySelection for extrascutellar bristles has resulted in two main levels of selection response, in several sets of lines. Crosses between these lines have shown that there are two genetic systems controlling the number of scutellar bristles.Two components of the selection advance have been compared at different levels of the background genotype, and one, the A9 component, shows a marked correlation of its effect with deviation from the norm of four bristles, having little if any effect at the norm and a marked effect at a mean of six bristles. The other component (the A15 component) did not show such a correlation.

A series of experiments of selection of scutellar bristles in D. melanogaster is described. The evidence suggest that there are three levels at which artificial selection is relatively ineffective and that these levels are not necessarily a function of homozygosity but rather of natural selection maintaining the line at a new equilibrium value. Crosses between the initial set (A set) of selection lines led to the conclusion that there is a consistent dominance of the parent with the lower scutellar value.Inversion-marked chromosomes were used to determine the location of selection advance on chromosomes I, II, and III. In the lines which had reached the highest level of selection advance the most effective chromosomes were chromosomes I and III or a combination of each of these. The lines which had reached the second level showed a marked heterogeneity of response, which included large negative components resulting from interchromosomal interactions.