Q.47 An ideal cybrid should have
(A) both nuclear genome and cytoplasmic genome equally from both the parents
(B) nuclear genome from one of the parents and cytoplasmic genome from other parent
(C) nuclear genome predominantly/exclusively from one of the parents and cytoplasmic genome
equally from both the parents
(D) nuclear genome equally from both the parents and cytoplasmic genome predominantly/
exclusively from one of the parents

Correct Answer: (B) nuclear genome from one of the parents and cytoplasmic genome from other parent

An ideal cybrid, or cytoplasmic hybrid, combines the complete nuclear genome from one parent with the cytoplasmic genome (mitochondria and chloroplasts) from the other parent. This asymmetric fusion allows targeted transfer of cytoplasmic traits like male sterility or disease resistance without mixing nuclear genomes, which is key in plant breeding.

Option Analysis

(A) both nuclear genome and cytoplasmic genome equally from both the parents: This describes a somatic hybrid from symmetric protoplast fusion, not a cybrid, as it mixes both genomes fully and often leads to instability.

(B) nuclear genome from one of the parents and cytoplasmic genome from other parent: Correct for ideal cybrids; the recipient protoplast provides the nucleus, while the donor (often irradiated) contributes cytoplasm, ensuring exclusivity.

(C) nuclear genome predominantly/exclusively from one of the parents and cytoplasmic genome equally from both the parents: This reverses the cybrid goal; equal cytoplasmic mixing defeats the purpose of isolating one parent’s organelles.

(D) nuclear genome equally from both the parents and cytoplasmic genome predominantly/exclusively from one of the parents: This mixes nuclei while segregating cytoplasm, which is inefficient and not the standard cybrid definition.

An ideal cybrid should have nuclear genome from one parent and cytoplasmic genome from other, enabling precise transfer of traits like herbicide tolerance via protoplast fusion in biotechnology. This technique bypasses sexual incompatibility in plants, revolutionizing breeding programs.

Cybrid Formation Process

Cybrids form through asymmetric fusion:

• Donor protoplasts are irradiated to destroy the nucleus.

• Recipient protoplasts retain their nucleus.

• Fusion yields cells with recipient nucleus and donor cytoplasm.

Key Applications

• Cytoplasmic male sterility (CMS) transfer for hybrid seeds.

• Disease or pest resistance from wild relatives.

• Organelle genetics studies in research.

Advantages Over Hybrids

Cybrids maintain nuclear stability while isolating cytoplasmic effects, unlike somatic hybrids prone to chromosome elimination.