Practice question

A merodiploid is a partially diploid bacterium possessing complete chromosome plus additional homologous DNA fragment introduced via F-prime plasmid conjugation, specialized phage transduction, or transformation. Jacob and Monod constructed F' lacI+ lacO+ lacZ+ / chromosome lac mutants to test dominance relationships and cis versus trans action of alleles. Recipient cell maintains overall haploid background but becomes heterozygous specifically for lac region, allowing complementation analysis of diffusible repressor protein versus non-diffusible operator DNA sites. Merodiploidy provided critical experimental tool establishing negative control, operator as cis-acting regulatory element, and foundations of operon theory.