Biological Systems MCAT Practice Exam

Which of the following is true regarding mitochondrial linked traits?

1. Inherited only from the father

2. Inherited only from the mother

3. Exclusively affects males

4. Passed down equally from both parents

The correct answer is: Inherited only from the mother

Mitochondrial linked traits are indeed inherited only from the mother. This is because mitochondria, the energy-producing organelles within cells, are primarily passed down through the oocyte (egg) during fertilization. The sperm contributes very little to the zygote's mitochondrial content, resulting in maternal inheritance for mitochondrial DNA. Mitochondria have their own distinct DNA, which is separate from nuclear DNA, and this mitochondrial DNA (mtDNA) is inherited from the mother. Consequently, any mutations or traits associated with mitochondrial DNA will be expressed in offspring derived from the maternal lineage. This pattern of inheritance accounts for certain genetic disorders that can be traced through maternal lines, affecting both males and females who inherit these traits. The other response options misinterpret the principles of mitochondrial inheritance: paternal inheritance would suggest that traits could be passed down from fathers, but this is not the case with mitochondrial DNA. Similarly, the notion that these traits exclusively affect males or are passed down equally from both parents contradicts the understanding of maternal inheritance. Thus, the clarity and specificity of maternal inheritance make the choice regarding inheritance strictly through the mother the correct one.