Further scrutiny of members of this family reveals the following: 1) The disease
ID: 100360 • Letter: F
Question
Further scrutiny of members of this family reveals the following: 1) The disease's degree of expression varies among individuals, with some mildly affected, others moderately affected and still others severely affected: and 2) Individual III-14 was previously married. Her ex-husband is phenotypically normal, with no history of the disease in his family going back ten generations. He has custody of the couple's two children, a girl and a boy, both of whom are affected with the disease. The partial pedigree is shown below (the "slash" represents separation or divorce) b. Do these findings eliminate any of the remaining "likely or unlikely" modes of inheritance listed in part (a)? Are any of these modes of inheritance still possible? If so, which one(s) and why? c. Is mitochondrial inheritance a likely, unlikely or an impossible mode of inheritance for this disease? Does it provide an explanation for the disease's variable expressivity? d. How can mitochondrial inheritance explain individual III-14?Explanation / Answer
c. Yes It is likely mitochondrial inheritence. Mitochondria is a double membrane organelle present in the cell's cytoplasm. It is responsible for cellular respiration. ATP generation takes place in the mitochondria. Mitochondria contains its own DNA which encodes many important protein. Mitochondrial replication does not depends on cell cycle. Mitochondria divide continually in the cell. Number of mitochondria cell to cell can vary according to energy need of the cell.
In Human, During reproduction mitochondrial DNA is inherited from the mother because the cytoplasmic factors are contributed by the oocyte only. Father do not pass mitochondria to offspring it only transmit nuclear genes.
In this pedigree, Disease is only passing to next generation when mother is affected. Father is not contributing this trait to affected offspring. Its is evident from the third generation where 4th and 10th father are affected while their offsprings are unaffected.
As the no. of mitochondria can vary cell to cell. When the egg is developing their normal and mutant mitochondria can present. Its depends on the no. of mutant mitochondria present in that cell which leads to variable expression of the disease in the individual.
d. As previously explained, the no. of mutant mitochondria can vary with the cell. During gamete development of III-14, their may be less no. mutant mitochondria are present. As the some proportion of mutant mitochondria can be tolerated in the cell this progeny appears to be normal.
As the III-14 individual contains mutant mitochondria and the gametes of III-14 with more no. of mutant mitochondria will have affected offspring so IV-15 and IV-16 are affected.
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