Lampbrush chromosome

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A Lampbrush chromosome(first seen by flemming) is a large chromosome (largest) found especially in the oocytes (immature eggs) of amphibians, birds and other animals. Lampbrush chromosomes occur during the diplotene stage of meiosis I. Lampbrush chromosomes are meiotic bivalents, each consisting of 2 sister chromatids. Each halve-bivalent is represented by two long strands that form many brushlike loops along the main axis of the chromosome. The outgrowths make DNA available for transcription during the maturation of the egg. Usually there is a little gene expression at meiosis, so it is not so easy to identify the activities of individual genes. Giant chromosomes in the lampbrush form can solve this problem, since they allow the individual transcription units to be examined. Lampbrush and chromosomal puffs in a cell indicate that the transcription of mRNA is taking place.

For more information see http://www.projects.ex.ac.uk/lampbrush/