Why is mitochondrial DNA inherited only from the mother?

Why is mitochondrial DNA inherited only from the mother?

• A. Mitochondria are inherited through the egg; sperm mitochondria are not transmitted
• B. Mitochondria are encoded in the nucleus
• C. Sperm contributes all mitochondria
• D. Mitochondria are inherited from both parents equally

Answer: (A)

Mitochondrial DNA is inherited through the mother because the embryo’s mitochondria come almost entirely from the egg’s cytoplasm. The egg provides a large pool of mitochondria and mtDNA to the zygote, while the sperm’s mitochondria (located mainly in the tail) are not transmitted to the embryo or are actively degraded after fertilization. Since mitochondria carry their own circular genome, inheritance is cytoplasmic rather than following Mendelian nuclear inheritance. In humans, paternal mitochondria are typically tagged for destruction, so the maternal line remains the source of mtDNA. The other statements don’t fit because mitochondria do have their own genome, paternal mitochondria are not normally transmitted, and mtDNA is not inherited equally from both parents.

Mitochondrial DNA is inherited through the mother because the embryo’s mitochondria come almost entirely from the egg’s cytoplasm. The egg provides a large pool of mitochondria and mtDNA to the zygote, while the sperm’s mitochondria (located mainly in the tail) are not transmitted to the embryo or are actively degraded after fertilization. Since mitochondria carry their own circular genome, inheritance is cytoplasmic rather than following Mendelian nuclear inheritance. In humans, paternal mitochondria are typically tagged for destruction, so the maternal line remains the source of mtDNA. The other statements don’t fit because mitochondria do have their own genome, paternal mitochondria are not normally transmitted, and mtDNA is not inherited equally from both parents.