Unraveling Poky Mutation Inheritance in Neurospora crassa: Mitochondrial Genetics Explained

The poky mutation in Neurospora crassa causes slow growth and follows a non-Mendelian pattern where progeny phenotypes depend solely on the maternal parent, pointing to cytoplasmic inheritance via mitochondria.​

Correct Answer

The inheritance mode of poky is (C) Mitochondrial inheritance. Crosses show that all progeny inherit the poky phenotype from poky females regardless of the male parent, as seen in (3) poky ♀ × wild-type ♂ → all poky and (4) poky ♀ × poky ♂ → all poky, while wild-type females produce wild-type progeny even with poky males.​

Cross Results Analysis

In Neurospora crassa, female parents contribute most cytoplasm, including mitochondria, to zygotes. Thus, (1) and (2) yield wild-type due to normal maternal mitochondria, whereas (3) and (4) transmit defective mitochondrial ribosomes from poky mothers, causing slow growth.​

Option Breakdowns

Episomal Inheritance

Episomal inheritance involves plasmids or extrachromosomal elements that replicate independently but can integrate into nuclear DNA. Poky does not fit, as it strictly maternal and tied to stable mitochondrial genomes, not episomes.​

Mendelian Inheritance

Mendelian inheritance follows nuclear chromosomal segregation with 1:1 or 3:1 ratios in F1/F2. Poky ignores paternal input and shows 100% maternal transmission, ruling out nuclear genes.​

Mitochondrial Inheritance

Mitochondrial inheritance transmits via maternal cytoplasm, as egg cells provide nearly all organelles. Poky arises from mitochondrial rRNA gene mutations impairing ribosome assembly, matching the cross data perfectly.​

X-Linked Inheritance

X-linked traits show sex-biased patterns like criss-cross inheritance. Neurospora lacks sex chromosomes, and poky affects all progeny equally from affected mothers, excluding this option.​