In polytene chromosomes, deficiency loops allow one to determine the size of the segment missing. The illustration above shows a portion of the X chromosome from the nucleus of a salivary gland cell of a Drosophila larva structurally heterozygous for a deficiency. Note that bands C2–C11 are missing from the lower chromosome.
Deficiency loop. From Principles of Human Genetics, 2nd ed., by Curt Stern. © 1960, 1973, 1980. Used with permission of W. H. Freeman and Company.
Subjects: Genetics and Genomics.