is then reflected in quantitative (such as mtdna copy number and mtdna deletions), qualitative (such as mutations and strand breaks) and oxidative damage (such as dysfunctional mitochondria due to ros), which are not only relevant in ovarian aging, but perturb oocyte-cumulus crosstalk in the ovary, are linked to genetic disorders (such as fragile x) and can interfere with embryo selection. history the first observations of intracellular structures that probably represented mitochondria were published in 1857, by the physiologist albert von kolliker. richard altmann, in 1890, established them as cell organelles and called them "bioblasts". in 1898, carl benda coined the term "mitochondria" from the greek μίτος, mitos, "thread", and χονδρίον, chondrion, "granule". leonor michaelis discovered that janus green can be used as a supravital stain for mitochondria in 1900. in 1904, friedrich meves, made the first recorded observation of mitochondria in plants in cells of the white waterlily, nymphaea alba and in 1908, along with claudius regaud, suggested that they contain proteins and lipids. benjamin f. kingsbury, in 1912, first related them with cell respiration, but almost exclusively based on morphological observations. in 1913, particles from extracts of guinea-pig liver were linked to respiration by otto heinrich warburg, which he called "grana". warburg and heinrich otto wieland, who had also postulated a similar particle mechanism, disagreed on the chemical nature of the respiration. it was not until 1925, when david keilin discovered cytochromes, that the respiratory chain was described. in 1939, experiments using minced muscle cells demonstrated that cellular respiration using one oxygen molecule can form four adenosine triphosphate (atp) molecules, and in 1941, the concept of the phosphate bonds of atp being a form of energy in cellular metabolism was developed by fritz albert lipmann. in the following years, the mechanism behind cellular respiration was further elaborated, although its link to the mitochondria was not known. the introduction of tissue fractionation by albert claude allowed mitochondria to be isolated from other cell fractions and biochemical analysis to be conducted on them alone. in 1946, he concluded that cytochrome oxidase and other enzymes responsible for the respiratory chain were isolated to the mitochondria. eugene kennedy and albert lehninger discovered in 1948 that mitochondria are the site of oxidative phosphorylation in eukaryotes. over time, the fractionation method was further developed, improving the quality of the mitochondria isolated, and other elements of cell respiration were determined to occur in the mitochondria. the first high-resolution electron micrographs appeared in 1952, replacing the janus green stains as the preferred way to visualize mitochondria. this led to a more detailed analysis of the structure of the mitochondria, including confirmation that they were surrounded by a membrane. it also showed a second membrane inside the mitochondria that folded up in ridges dividing up the inner chamber and that the size and shape of the mitochondria varied from cell to cell. the popular term "powerhouse of the cell" was coined by philip siekevitz in 1957. in 1967, it was discovered that mitochondria contained ribosomes. in 1968, methods were developed for mapping the mitochondrial genes, with the genetic and physical map of yeast mitochondrial dna completed in 1976.