Define a cistron . Giving examples differentiate between monocistronc and polycistronic unit.

Explanation

Cistron represents the fragment of DNA which forms a single polypeptide and is equivalent to structural gene. Transcription unit is monocistronic (with single structural gene) e.g., eye colour in Drosophila and height in pea plants.
Transcription unit is polycistronic (with many structural genes) e.g., lac operon, trp operon, ara operon, his operon. Monocistronic unit is common in eukaryotes and polycistronic units are common in prokaryotes.