Question

Lampbrush Chromosomes are observed in-
a. Meiotic metaphase
b. Mitotic metaphase
c. Mitotic prophase
d. Meiotic prophase

Answer 1

Hint: Its formation occurs in a stage in which the CHROMATIDS becomes separated (except at the CHIASMATA), and the chromosomal material is contracting. The chiasmata normally specify that crossing over is taking place. In this stage, the two homologous chromosomes start to migrate away from each other with the 'synaptonemal complex' disintegrates between the two chromosomal arms and they begin to push back one another.

Complete answer:
Lampbrush chromosomes are mostly found in the growing oocytes of most animals, except mammals. The shape of LBCs is attained due to the active transcription of many genes during diplotene stages. They are hugely extended meiotic half-bivalents, each having 2 sister chromatids.

Chromosomes transform into the lampbrush form during the diplotene stage of the meiotic prophase I due to active transcription of many genes. They are highly extended meiotic half-bivalents; each comprises 2 sister chromatids.

In metaphase in mitosis and meiosis, the chromosomes compact and they become observable and noticeable during alignment at the middle of the dividing cell, to shape a metaphase plate at the center of the cell. Prophase is the initial phase of mitosis, the process that divides the duplicated genetic material carried in the nucleus of a parent cell into two identical daughter cells.

All other options are wide of the mark because during the chiasmata formation which occurs only in the Meiotic Prophase stage. By this, the recombination of paternal and maternal genes can be passed down to the progeny.

Hence, the correct answer is option (D).

Note: Lampbrush chromosomes are transcriptionally active chromosomes generally found in the germinal vesicle (GV) of large oocytes of several vertebrate and invertebrate animals. These cells are all present in prophase of the first meiotic division. Lampbrush Chromosomes (LBCs) provide unique opportunities to study thoroughly about reprogramming at the level of the individual transcription unit.