The pedigree is a diagram showing a subject trait as it is shown across generations of a family. In this diagram, males are represented by squares and females are represented by circles. The individuals who show the trait are shown as shaded shapes.
Given the information about mitochondrial inheritance as an example of extrachromosomal inheritance, answer the questions that follow.
- Mitochondria contain their own DNA
- The female gamete (egg) contains cytoplasm and mitochondria
- The male gamete (sperm) has no cytoplasm or mitochondria, and is streamlined to a nucleus and flagellum-like structure for motility
- Thus, mitochondrial inheritance of daughters and sons must be traced back through the matrilineal line (mothers only)
The pedigree in the figure below shows a family in which an inherited disease called Leber's opticatrophy is segregating. This condition causes blindness in adulthood. Studies have recently shown that the mutant gene causing Leber's optic atrophy is located in the mitochondrial genome.
Assuming II-4 marries a normal person, what proportion of his offspring should inherit Leber's optic atrophy?
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