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Which of the following transmission patterns is most consistent with this female patients family history? (LQ)

A Autosomal recessive
B Autosomal dominant

C X-linked recessive
D Mitochondrial

Ans. D Mitochondrial (Robbins 8th Ed, pp 164165, 1287)

a. Almost all genes occur on chromosomes within the nucleus.

b. There are a few genes, however, that are located within the mitochondria.

c. These mitochondrial genes are found on mitochondrial DNA (mtDNA).

d. These genes are all of maternal origin, possibly because ova have mitochondria within the large amount of cytoplasm while sperm do not.

e. This maternal origin means that mothers transmit all of the mtDNA to both male and female offspring, but only the daughters transmit it further.

f. No transmission occurs through males.

g. Example: One disease associated with mitochondrial inheritance is Leber hereditary optic neuropathy (LHON), which is characterized by progressive bilateral loss of central vision and usually occurs between 15 and 35 years of age.