Fundamental interest in the molecular mechanisms involved in the evolution and function of developmental processes in mammals has led to two lines of research: the first, the t haplotype variant of mice and the second, gene conversion in mice. The t mutant has about 15 centiMorgans of chromosome 17 which contains multiple conversions relative to wild type mice and which is transmitted to nearly all offspring in a phenomenon called transmission ratio distortion. One of the most important of the genes in this complex has been cloned in this laboratory and it is being characterized by transgenic experiments. The second area of interest is being approached by an attempt to determine the frequency of intra- and interchromosomal meiotic gene conversion. Alternate promoters will be use to investigate the frequency of this form of recombination in various somatic cells in mice. These approaches represent new avenues for exploration of complex and important genetic events in mammals.***