what is knob heterochromatin?
Here's a good summary of knobs, which says that they are &quot;typically telomeric,&quot; &quot;tandemly repeated DNA sequences [that] appear as distinct, heteropycnotic regions located at certain sites on specific chromosomes and look much like beads on a string&quot; and are involved in:

increased recombination
neocentromere activity
preferential segregation
chromosome breakage and chromatin loss
sex differences in recombination

The introduction to this paper gives some of the same information.