Sugarcane smut (also known as culmicolous smut or whip smut) is caused by the basidiomycete fungus Sporisorium scitamineum (synonym: Ustilago scitaminea Sydow). The hallmark symptom is the transformation of the terminal shoot/growing point into a long, curved, black, whip-like unbranched structure (sorus) covered by millions of dark teliospores.

All the genes located linearly on a single chromosome are physically linked and tend to be inherited together as a unit known as a linkage group. Because homologous chromosomes contain corresponding allelic loci, a homologous chromosome pair constitutes a single linkage group. Therefore, the total number of linkage groups in an organism corresponds precisely to its haploid (gametic) chromosome number ($n$). For instance, garden pea ($2n=14$) has 7 linkage groups, and maize ($2n=20$) has 10 linkage groups.

In eukaryotic cells, RNA Polymerase II transcribes protein-coding structural genes into an immediate, primary transcript called heterogeneous nuclear RNA (hnRNA) or pre-mRNA. This nascent hnRNA contains both protein-coding exons and intervening non-coding introns. Before exporting to the cytoplasm as functional, translatable mRNA, hnRNA must undergo extensive post-transcriptional processing: 5'-capping (7-methylguanosine), 3'-polyadenylation, and spliceosome-mediated intron splicing.