Rare Inheritance Pattern Every Medical Student Should Know

In vertebrates, inheritance of mitochondria is thought to be predominantly maternal, and mitochondrial DNA analysis has become a standard taxonomic tool. In accordance with the prevailing view of strict maternal inheritance, many sources assert that during fertilization, the sperm tail, with its mitochondria, gets excluded from the embryo. This is incorrect. In the majority of mammals—including humans—the midpiece mitochondria can be identified in the embryo even though their ultimate fate is unknown. The “missing mitochondria” story seems to have survived—and proliferated—unchallenged in a time of contention between hypotheses of human origins, because it supports the “African Eve” model of recent radiation of Homo sapiens out of Africa. Most human anatomy textbooks correctly report that in mammals the entire sperm cell, including the mitochondria and flagellum, enters the egg at fertilization. However, these facts appear to have been ignored by some scholars of anthropology and human evolution. There have been many faulty iterations that the sperm tail (including the midpiece) plays no part in development. This error has even crept into standard texts on biochemistry. The misconception that all mtDNA inheritance must be maternal threatens future research. For example, Cann et al. give several reasons to establish the suitability of mtDNA for their study, one being, “… because mtDNA is inherited maternally and does not recombine, it is a tool for relating individuals to one another.” They claim “Molecular biology is now a major source of quantitative and objective information about the evolutionary history of the human species.” This error of obligatory maternal inheritance of mtDNA in humans appears to arise entirely from approaches using restriction fragment analysis. However, Gyllensten et al., using the PCR, detected paternally inherited mtDNA molecules in mice at a frequency of 1 in 10,000 , relative to the maternal contributions. They concluded: “Paternal inheritance of mtDNA also means that mtDNA phylogenies are not exclusively matriarchal.” Note that the paternal inheritance rate of 1 in 10,000. The myth of the missing midpiece seems to have been well established by the mid 1980s. In a review of the evolution of mtDNA in primates Spuhler declares: “Most models for the evolutionary genetics of mtDNA in mammalia assume that inheritance is strictly maternal. Although the sperm of vertebrates may contain hundreds of mitochondria in the middle-piece, usually that structure does not enter the fertilized egg, and if paternal mitochondria do enter, seemingly few, if any, survive the first equational cell division.” This is clearly incorrect. Indeed, the paper by Wilson et al. to which Spuhler refers neither provides concrete information nor gives any reason to explain why mtDNA inheritance should be strictly maternal. #sperm #Mitochondria #Dna #mtDNA #fertilization #MolecularBiology #cellDivision #Mutation #Genetics #biology #eggCell #TedEd #crashCourse #KhanAcademy #ShomusBiology #iBiology #MITOpenCourseWare #amoebaSisters #Osmosis #BozemanScience #OrganicChemistryTutor #PedigreeAnalysis #pedigreeAnalysisPractice #pedigreeAnalysisGenetics #pedigreeAnalysisProbability #pedigreeAnalysisAnswers #pedigree #pedigreeCharts #solvePedigreeProblems #analyzingPedigree