Lampborstel-chromosomen

Amphibians, like many other vertebrates, produce female gametes, or ova, which mature and develop within the ovary. 

At one particular developmental stage, meiotic prophase-I, homologous replicated chromosome pairs display a distinct morphology- an enormously extended structure, so gigantic that it can be easily observed under a light microscope

These very unusual chromosomes are called ‘lampbrush chromosomes’ due to their resemblance to the brushes used in earlier times to clean kerosene lamps. Due to their enormous size, they are ideal models for studying chromosomes.

These giant chromosomes are organized into a series of large lateral, uncoiled DNA loops all along the chromosome axis. In addition to these extended loops, dense, thick coiled loops are observed along the chromosomal axis, which constitute the majority of DNA. 

These two domains also differ greatly in the level of transcriptional activity. The genes in the lateral loops are actively transcribed, which gives them a fine fibrillar appearance. 

In contrast, the genes on the condensed chromosome axis are generally not expressed. 

Although they were first described in amphibians, these looped chromatin domains are now believed to occur in the interphase chromosomes of all eukaryotes. 

Due to their small size and fragile nature, the looped chromatin can’t be observed using a light microscope in most eukaryotes. Their presence has been inferred using modern DNA technologies such as ‘Chromosome Conformation Capture.'