Q.(a) Bring out the inheritance of chloroplast gene with an example. OR

(a) Chloroplast (cytoplasmic) inheritance is illustrated by maternally-inherited leaf variegation in Mirabilis jalapa; (b) single cell protein serves as a protein-rich food/feed supplement.

(a) Inheritance of the chloroplast gene

Chloroplasts, like mitochondria, carry their own small DNA genome and are inherited independently of the nuclear (Mendelian) genes, through a phenomenon called cytoplasmic (extranuclear/organelle) inheritance. The classic example, first studied by Carl Correns in 1908, is leaf variegation in the four o'clock plant, Mirabilis jalapa. This plant naturally produces branches bearing leaves of three types: fully green (normal chloroplasts), fully white/pale (defective, non-pigmented plastids), and variegated (a patchy mixture of green and white sectors).

When reciprocal crosses were made -- using flowers on branches of each leaf-colour type as either the female (egg-bearing) or male (pollen-bearing) parent -- the colour of the offspring's leaves was found to depend entirely on which branch supplied the female (ovule/egg) parent, regardless of which branch supplied the pollen:

• Female parent from a green branch -> all offspring green, whatever the pollen source.
• Female parent from a white branch -> all offspring white (often unable to survive long, lacking chlorophyll), whatever the pollen source.
• Female parent from a variegated branch -> offspring show a mixture of green, white, and variegated types, in varying proportions.

This result showed that the trait is transmitted only through the maternal (egg) parent, never through the pollen -- because during fertilisation, the pollen (male gamete) contributes essentially only its nucleus, while chloroplasts are carried in the cytoplasm of the much larger egg cell. Since chloroplasts (containing their own DNA and hence the genes for pigmentation) are passed on almost exclusively via the egg's cytoplasm, this is a clear example of maternal, non-Mendelian (cytoplasmic) inheritance, distinct from the biparental inheritance pattern of nuclear genes.

(b) Applications of single cell protein (SCP)

Single Cell Protein (SCP) refers to the dried, protein-rich cellular biomass obtained by cultivating microorganisms -- algae (e.g. Spirulina, Chlorella), yeasts (e.g. Candida utilis, Saccharomyces), bacteria (e.g. Methylophilus methylotrophus), or fungi -- on an industrial scale, often using cheap, renewable substrates such as molasses, whey, agricultural or food-processing waste.

Applications include: …