Question

In Neurospora crassa, a mutation in the poky gene results in slow growth (poky). The results of four crosses are given:
(1) wild-type ♀ × wild-type ♂ → All progeny wild-type
(2) wild-type ♀ × poky ♂ → All progeny wild-type
(3) poky ♀ × wild-type ♂ → All progeny poky
(4) poky ♀ × poky ♂ → All progeny poky
Which one of the following explains the inheritance mode of poky?

• A. Episomal inheritance
• B. Mendelian inheritance
• C. Mitochondrial inheritance
• D. X-linked inheritance

Hint:

If progeny always show the mother's phenotype regardless of the father, the inheritance is almost certainly mitochondrial.

Answer 1

The Correct Option is C

The key to determining inheritance mode is examining how the phenotype depends on the mother versus the father.

Step 1: Analyze the crosses.
- In cross (2), wild-type ♀ × poky ♂ → all progeny are wild-type. This indicates that the father's phenotype does NOT influence the progeny.
- In cross (3), poky ♀ × wild-type ♂ → all progeny are poky. This indicates that the mother's phenotype alone determines progeny phenotype.

Step 2: Identify the inheritance pattern.
A pattern where ONLY the mother determines the phenotype is a classic signature of cytoplasmic inheritance. In Neurospora, the poky mutation is famous for being inherited through mitochondrial DNA.

Step 3: Exclude other possibilities.
- Not Mendelian: Mendelian inheritance would follow predictable dominant–recessive patterns independent of sex of parent.
- Not X-linked: Neurospora is haploid during most of its life cycle and does not show X-linked patterns.
- Not episomal: episomal inheritance would not strictly depend on the mother.

Step 4: Conclusion.
The pattern fits mitochondrial inheritance, since mitochondria—and their DNA—are inherited maternally.