<prompt> Genes with purely or predominantly matrilineal inheritance without recombination are present in:X chromosomeY chromosomeMitochondrial chromosomeAll of the above  <response>: Ans. c Mitochondrial chromosome. Ref. Harpers Biochemistry 26th ed. 323; Ganong 22nd ed. 11, 27Inherited mitochondrial disorders are transmitted in a matrilineal fashion; all children from an affected mother will inherit the disease, but it will not be transmitted from an affected father to his children. Heterogeneity in the proportion of mitochondria with and without a mutation is referred to as heteroplasmia and underlies the phenotypic variability that is characteristic of mitochondrial diseases.MITOCHONDRIAL DNA mtDNA It is small circular, double-stranded, and composed of heavy and light chains. One percent of cellular DNA is in mitochondria. High mutation rate 5-10 times more than nuclear DNA. Genetic codes differ slightly from the standard code:- UGA standard stop codon is read as Trp.- AG A and AGG standard codon for Arg are read as stop codons.Diseases transmitted by mitochondrial inheritance: Lebers hereditary optic atrophy, Leigh disease, Familial progressive external ophthalmoplegia, MERRF syndrome, MEALS syndrome, Succinic dehydrogenase complex-II deficiency and Cytochrome C oxidase complex-IV dt. 