Ans: C (Transmit...) SINGLE-GENE DISORDERS WITH NONCLASSiC INHERITANCE Robbins 8th/l67It has become increasingly evident that transmission of certain single-gene disorders does not follow classic mendelian principles. This group of disorders can be classified into four categories:# Diseases caused by triplet-repeat mutationsDisorders caused by mutations in mitochondrial genesDisorders associated with genomic imprintingDisorders associated with gonadal mosaicismMitochondria DNA Harrison 17th /Part 18 e-39# The DNA sequence of mtDNA has been determined from a large number of organisms and individuals (including some organisms that are extinct), and the comparison of those DNA sequences represents a mainstay of phylogenetics, in that it allows biologists to elucidate the evolutionary relationships among species.Mothers transmit their mtDNA to both their sons and daughters, only the daughters are able to transmit the inherited mtDNA to future generations (Maternal inheritance)High somatic mtDNA mutation rate and the global effect on mitochondria! function counterbalance the reduced impact of the multiple copy number of each individual mtDNA mutation.This mtDNA sequence contains a total of 37 genes, of which 13 encode mitochondrial protein components of the ETC The remaining 22 tRNA- and 2 rRNA-encoding genes are dedicated to the process of translation of the 13 mtDNA- encoded proteins.The accumulation of functional mtDNA deletionsin a given tissue is expected to be associated with mitochondrial dysfunction, as reflected in an age-associated patchy and reduced cytochrome-c oxidase activity upon histochemical staining, especially in skeletal and cardiac muscle and brain.Table : (Harrison 17th /Part 18 e-39 ): Mitochondrial Diseases Due to mtDNA Point Mutations and Large-Scale RearrangementsDiseasePhenotypeLeber hereditary optic neuropathy (LHON)Loss of central vision leading to blindness in young adult lifeNARP, Leigh's diseaseNeuropathy, ataxia, retinitis pigmentosa, developmental delay, mental retardation, lactic acidemiaMELASMitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes: may manifest only as diabetesMERRFMyoclonic epilepsy, ragged red fibers in muscle, ataxia, increased CSF protein, sensorineural deafness, dementiaDeafnessProgressive sensorineural deafness, often induced by aminoglycoside antibiotics. Nonsyndromic sensorineural deafnessChronic progressive externalophthalmoplegia(PEO)Late-onset bilateral ptosis and ophthalmoplegia, proximal muscle weakness, and exercise intolerancePearson syndromePancreatic insufficiency, pancytopenia, lactic acidosisKeam-Sayre syndrome (KSS)External ophthalmoplegia, heart-block, retinal pigmentation, ataxia