Embryo Project Encyclopedia

All cells that have a nucleus, including plant, animal, fungal cells, and most single-celled protists, also have mitochondria. Mitochondria are particles called organelles found outside the nucleus in a cell's cytoplasm. The main function of mitochondria is to supply energy to the cell, and therefore to the organism. The theory for how mitochondria evolved, proposed by Lynn Margulis in the twentieth century, is that they were once free-living organisms. Around two billion years ago, mitochondria took up residence inside larger cells, in a process called endosymbiosis, becoming functional parts of those cells. Within each mitochondrion is the mitochondrial DNA (mtDNA), which is different from the DNA in the cell's nucleus (nDNA). Organisms inherit their mitochondria only from their mothers via egg cells (oocytes). Mitochondria contribute to the development of oocytes, the release of the oocyte from the ovary (ovulation), the union of oocyte and sperm (fertilization), all stages of embryo formation (embryogenesis), and growth of the embryo after fertilization.

Lysogenic bacteria, or virus-infected bacteria, were the primary experimental models used by scientists working in the laboratories of the Pasteur Institute in Paris, France, during the 1950s and 1960s. Historians of science have noted that the use of lysogenic bacteria as a model in microbiological research influenced the scientific achievements of the Pasteur Institute's scientists. Francois Jacob and Jacques Monod used lysogenic bacteria to develop their operon model of gene regulation, to investigate the cellular regulatory mechanisms of the lysogenic life cycle, and to infer the process of cellular differentiation in the development of more complex eukaryotes.