LAMPBRUSH CHROMOSOME

What is Lampbrush chromosome? 

 

Giant  chromosome - 

 Some cells at certain particular stages contains large nuclei with giant or large sized chromosome. 

                   The giant chromosome are the polytene and Lampbrush chromosome. 

  

- It found in certain tissue eg. Salivary gland of larvae, gut epithelium, malphigian tubules and some fat bodies, some Diptera ( Drosophilla, sciara, Rhyncosciara) 

- These chromosome are very long and thick (up to 200 times of their size during mitotic metaphase in the case of Drosophilla.) 

- Hence they are known as Giant chromosome. 

Lampbrush chromosome:-

- It is similar in appearance to the brush used to clean lamp chimney in past century. 

- Frist observed by Flemming in 1882 . 

 ( salamander egg cell - Amblystoma maxicanum  ). 

- The name Lampbrush was given by Ruckert in 1892.

- Also found in plants, but most experiment in oocytes. 

 Structure of Lampbrush chromosome-

1) Lampbrush chromosome are intermediate structure present during the frist mitotic division. 

2) They are present in the form of bivalent in which the maternal and paternal chromosome are held together by Chismata. 

3) Central axis consist of two bivalent homologous chromosome each with two chromatid so all together there are four chromatid. 

4) From each chromosome, a pair of loops emerges in opposite directions vertical to the main chromosomal axis. 

5) Usually, 1-9 loops may arise from each chromosome. 

6) The lateral loops contains a fully extended DNA duplex. They are believed to be formed by Uncoiling of the sister chromatid. 

7) Lateral loops contains bundle of sub microscopic fibrils. 

8) Both the central axis and the loop axis are formed of Deoxyribose protein. It may me coated with matrix of RNA and protein. 

9) The lateral loops are active site of RNA synthetis and each loop may contain one or more transcription unit. 

10) Newly synthesized RNA molecule associated with protein and form a ribonucleoprotein. 

11) Lampbrush chromosome are up to 800 um

Long, thus they provide very favorable material for cytological studies. 

- It used to studying transcription. 

- Room temperature 21-24°c have larger loops in frog. 

- At higher temperature 28-32 °c helped to bring about the maximal expansion of the loop. 

- The size of the loop may be ranging the average of 9.5 um to about 200 um.

 

12) Lampbrush chromosome are belived to govern the synthetmsis activity of growing oocytes. 

13) Lampbrush chromosome are also show the possible way of the gene amplification which required during the growth phase of oocytes.