Maternal inheritance

Non-Mendelian inheritance is a general term that refers to any pattern of inheritance in which traits do not segregate in accordance with Mendel’s laws. These laws describe the inheritance of traits linked to single genes on chromosomes in the nucleus. In Mendelian inheritance, each parent contributes one of two possible alleles for a trait. If the genotypes of both parents in a genetic cross are known, Mendel’s laws can be used to determine the distribution of phenotypes expected for the population of offspring. There are several situations in which the proportions of phenotypes observed in the progeny do not match the predicted values.
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Diseases due to mutations in mtDNA are transmitted only by mothers because all mitochondria are inherited via the egg. Thus, all offspring of an affected female are at risk of inheriting the abnormality, whereas no offspring of an affected male are at risk. Clinical manifestations are variable and may be due to variable mixtures of mutant and normal mitochondrial genomes (heteroplasmy) within cells and tissues.