Question

Draw and label the structure of lampbrush chromosomes.

Answer 1

Hint: Lampbrush chromosomes are transcriptionally active chromosomes. They are found in prophase 1 of the meiotic division. They represent the most active transcriptional state that can be achieved by cells that would give rise to diploid progeny. They are transformed during the diplotene stage of meiotic prophase- 1.

Complete answer:
Lampbrush chromosomes are found in growing oocytes (immature eggs) of most animals. Chromosomes transform into a lampbrush during the diplotene stage of meiotic prophase - 1. They are transcriptionally active chromosomes.
- Lampbrush chromosomes were described by Walther Flemming in 1892. They are highly extended meiotic half bivalents, both consisting of two sister chromatids each. They are clearly visible under the light microscope.
- It is named as lampbrush chromosome because when it is seen under a light microscope it appears as a lampbrush.
- It is formed as a normal chromosome and during transcription, it is transformed into a lampbrush chromosome during meiotic prophase- 1 in the diplotene stage.
- Lampbrush chromosomes are seen in growing oocytes of animals- basically amphibians (not in mammals) lower vertebrates and invertebrates.
- RNA synthesis (i.e., transcription process) takes place within the two chromatid loops. Within the DNA strand, chromomere is present. Chromomere is the point where two chromatid sisters are fused. Within the chromatid loop, RNA synthesis (i.e., the transcription process) takes place.
- Lampbrush chromosomes are widely used for high- resolution mapping of DNA sequences and in the construction of detailed cytological maps of individual chromosomes.
- It also helps in understanding the chromosomal organization, genome organization, and gene expression.

Note: Lampbrush chromosomes are not found in mammals, they are found in growing oocytes of amphibians. They represent active chromosomes. They are not produced as such rather they are formed as normal chromosomes and these normal chromosomes transform into lampbrush chromosomes during the meiotic prophase- 1 stage.