Q.(a) What is crossing over ? Give the diagrammatic representation of crossing over. OR

(a) Crossing over exchanges segments between non-sister chromatids at a chiasma during meiosis I; (b) single cell protein is microbial biomass used as a cheap, protein-rich food/feed supplement.

(a) Crossing over -- definition and diagrammatic representation

Crossing over is the process by which genetic material is exchanged between two non-sister chromatids of a pair of homologous chromosomes, occurring during the pachytene stage of prophase I of meiosis, after the homologous chromosomes have paired up (synapsis) to form a bivalent/tetrad. This exchange results in genetic recombination -- chromatids carrying new combinations of alleles that differ from either parental chromosome.

Since an actual diagram cannot be drawn here, its representation is described element by element: two homologous chromosomes are shown paired closely together (synapsed), each consisting of two sister chromatids joined at a common centromere, so that the paired structure (a bivalent) shows four chromatids in total. At one or more points along the length of the bivalent, two of the chromatids -- one from each homologous chromosome, i.e. non-sister chromatids -- physically cross over each other, forming an X-shaped point of contact called a chiasma. At the chiasma, the DNA of the two crossing chromatids is broken and reunited in a new combination, so that beyond the chiasma point, each of those two chromatids now carries a segment originally belonging to the other homologue. After the bivalent separates, this produces two recombinant chromatids (with a new mix of parental alleles) alongside the two original, unchanged parental (non-recombinant) chromatids.

(b) Single cell protein (SCP) -- definition and applications

Single cell protein (SCP) refers to the dried, protein-rich cellular biomass obtained by culturing microorganisms -- algae (e.g. Spirulina, Chlorella), bacteria, yeasts or other fungi -- on an inexpensive growth substrate (such as molasses, whey, agricultural residues or industrial waste), harvested and processed as a rich source of protein for consumption.

Applications:

1. Human food supplement: SCP (e.g. Spirulina) is used as a nutritional supplement, being very rich in protein, vitamins and minerals, and is promoted as a way to combat protein-energy malnutrition. …