Question

Give a brief note on lampbrush chromosomes.

Answer 1

Hint:Lampbrush chromosomes are the giant chromosome found only in the special tissues in the eukaryotic organisms. These chromosomes are larger in size and are found in growing oocytes of animals except mammals.

Complete Answer:
Lampbrush chromosomes were first discovered by Walther Flemming in 1882. The chromosomes transform into the lampbrush during the diplotene stage of meiotic prophase I. This transformation is due to the active transcription of many genes.
Structure-
They are meiotic half bivalents. It consists of 2 sister chromatids. As seen through the light microscope, they are arranged in a series of chromomeres having large extended chromatin loops. Each lateral loop has one or several transcription units, a coating of polarised RNP matrix over the DNA axis.
Function-
They can be easily isolated from the oocyte nucleus with a forceps or needle.
They are useful in studying the chromosome organisation, genome and gene expression during meiotic prophase.
They are widely used for high resolution DNA mapping and in constructing detailed cytological maps of individual chromosomes.

Additional Information:
Another giant chromosome called the polytene chromosome is present in the larvae of dipterans. They are relatively smaller than the lampbrush chromosomes. The polytene chromosomes have Balbiani rings. These are the active sites for RNA synthesis. It is present in the saliva And they synthesise unusually large proteins.

Note:The lampbrush chromosomes are majorly seen in the oocytes of the bird, lower vertebrates and invertebrates during the prophaseI of meiosis. They look similar to the bottle brush so they are called lampbrush chromosomes.