Lampbrush Chromosome Structure and Function

In this lampbrush chromosome structure and function post we have briefly explained about lampbrush chromosome definition, lampbrush chromosome diagram, lampbrush chromosome structure and function.

Lampbrush Chromosome Definition

History of Lampbrush Chromosome

Lampbrush Chromosome Structure

Functions of Lampbrush Chromosome

Lampbrush Chromosome Definition

Lampbrush Chromosome definition as type of chromosome that is found in the developing oocytes (immature eggs) of all animals except mammals. Walther Flemming described them for the first time in 1882. 

The lampbrush chromosomes of tailed and tailless amphibians, birds, and insects are best described. Because of active transcription of many genes, chromosomes transform into the lampbrush form during the diplotene stage of meiotic prophase I.

History of Lampbrush Chromosome

They were first of all reported by Walther Flemming (German biologist and a founder of cytogenetics) in 1882 in Salamander (Ambystoma mexicanum). Ten years later they were described in the oocytes of a dogfish by Ruckert (1892) and named them lampbrush.

Lampbrush chromosomes

Lampbrush Chromosome diagram A. Enlarged view of a part of lampbrush chromosome, B. Single loop of lampbrush chromosome

Lampbrush chromosomes have been best characterized in tailed and tailless amphibians, insects and birds. Lampbrush chromosomes are found at diplotene stage of meiotic prophase in primary oocytes and also in spermatocytes of many invertebrates and vertebrates.

In meiotic prophase, they are present in the form of bivalents in which the maternal and paternal chromosomes are held together by Chiasmata and each bivalent has four chromatids. Beside animals lampbrush chromosomes are also found in few plants such as Acetabularia. Lampbrush chromosomes of different species are almost similar in structure and function however loop length is species specific i.e., it may vary from species to species.

Lateral loops give the appearance of a lampbrush (Diagram of lampbrush chromosome:1). Lateral loops extrude in pairs from each sister chromatid. Loops are symmetrical; each loop is a single linear thread of DNA that runs through each chromatid.

The loops are extruded part of DNA which is being actively transcribed, therefore they are surrounded by matrix of ribonucleoproteins (RNP). These chromosomes are quite long in length, their length may range between 800-1000µ. They are the largest known chromosomes. Later they revert back to their normal size.

Lampbrush Chromosome Structure

Each lampbrush chromosome consists of two homologous chromosomes (lampbrush chromosome diagram:1). Each homologue has two chromatids. Both the homologous chromosomes are joined to one another at several points called Chiasmata. Otherwise they are separated.

Lampbrush chromosomes appear brush like because of threads that loop out from two chromatids (lampbrush chromosome diagram:1). These loops always occur in pairs. Loops in lampbrush chromosomes are made up of DNA associated with RNA and ribosome and also act as site of transcription.

It has been experimentally proved that each loop is made up of single DNA double helix. Chromosomal axis bears string of fine chromatin granules known as chromomeres. One or many pairs of loops arise from each chromomere.

Functions of Lampbrush Chromosome

There are two main functions of Lampbrush chromosomes one being synthesis of RNA and other formation of yolk material.

RNA synthesis: Through the loop region of Lampbrush chromosome, synthesis of RNA (transcription) occurs. One end of loop of Lampbrush chromosome is thin while the other end is thick. Most of the RNA synthesis occurs at thin ends of loop however, there is little or no RNA synthesis at thicker end of loops. Formation of yolk material: Lampbrush chromosome are believed to help in formation of yolk material in egg.

The answer to the question of structure and function of lampbrush chromosome has been found. You can learn more about chromosomes and functions at NotesHippo.com