Lamp brush chromosomes were observed
in Salamander (amphibian) oocytes in 1882. Lamp brush
chromosomes are look like the brushes which were used for cleaning purpose. Lamp
brush chromosomes occur at the diplotene stage of meiotic prophase in the
primary oocytes and spermatocytes of many vertebrates and invertebrates. They
were observed even in some plants like Acetabularia.
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| Lamp Brush Chromosomes |
A lamp brush chromosome actually
contains two homologous chromosomes. The two homologous have separated except at
several joined points chiasmata. Each homologue at this stage has two
chromatids. The lamp brush appearance of the two homologues in a chromosome is
the result of the threads that loop out from its two chromatids. The loops occur
in pairs. The loops are made up DNA with associated RNA and ribosomes, and are
sites of transcription. The axis of the chromosome consists of a string of fine
chromatin granules called chromomeres. One or many pairs of loops extend from
each chromomere. In this arrangement each chromatid consists of a sting of
chromomeres with attached loops.
Since the two chromatids are tightly
opposed to each other, the chromosome axis is probably by fused pairs of
chromomeres. Experimental evidences show that each loop is single DNA double
helices.
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ReplyDeletegood explanation THANKU
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