Extrachromosomal Inheritance Questions and Answers

Answer: D

Cytoplasmic male sterility arises from the interaction of the nucleus and mitochondria.

CMS is caused by rearranged, chimeric open reading frames in the mitochondrial genome that disrupt pollen development. Whether the plant is actually male sterile depends on its nuclear genotype: dominant nuclear restorer-of-fertility (Rf) genes can suppress the mitochondrial defect. This nucleo-mitochondrial interplay is what makes CMS useful in hybrid seed production of maize, rice and sunflower.

Plastids and the Golgi are not the source of the sterility factor, so the options pairing the nucleus with them, or mitochondria with plastids, are wrong.

Answer: D

RuBisCO is encoded by Nuclear DNA and Chloroplast DNA.

Plant RuBisCO has eight large and eight small subunits. The large subunit, which carries the catalytic site, is encoded by the chloroplast gene rbcL and made on chloroplast ribosomes. The small subunit is encoded by a family of nuclear rbcS genes, made in the cytosol with a transit peptide and imported into the chloroplast, where the two are assembled.

The mitochondrial genome encodes respiratory chain and ribosomal components, not RuBisCO, so every option mentioning mitochondrial DNA is wrong. 'Plastid DNA' is right for the large subunit only, which is why the option pairing it with mitochondrial DNA fails.

Answer: A

Cytoplasmic inheritance involves the mitochondria.

Mitochondria contain their own circular DNA. Because the egg contributes nearly all the cytoplasm of the zygote, mitochondrial genes are passed on through the mother, giving maternal inheritance. Chloroplasts in plants are the other classic example.

The Golgi body, lysosomes and endoplasmic reticulum have no genome of their own, so they cannot carry heritable genes, even though they too are passed on in the egg's cytoplasm.