Question

Describe the structure of lampbrush chromosomes. Where are they located?

Short answer

Answer: The primary function of lampbrush chromosomes during the meiotic prophase of oocyte nuclei is to synthesize large amounts of RNA required for the early development of the embryo after fertilization.

Step-by-step solution

1. Definition of Lampbrush Chromosomes

Lampbrush chromosomes are a specific type of chromosome found during the meiotic prophase of oocyte nuclei in animals. They are named "lampbrush chromosomes" due to their appearance, which is similar to a test tube brush or a lamp cleaner.

2. Structure of Lampbrush Chromosomes

Lampbrush chromosomes consist of chromatin fibers that are organized into loops called chromomeres. These chromomeres extend out from the chromosome axis, forming a brush-like structure. Each chromomere loop consists of DNA, RNA, and proteins. In each loop, transcription takes place, meaning that the DNA in the loop is used as a template to synthesize RNA. This process produces numerous RNA transcripts along the loop, which leads to the formation of structures called RNP-matrix. The RNP-matrix consists of RNA and proteins and is responsible for the lampbrush appearance.

3. Loops and Chromomeres

Loops of lampbrush chromosomes can be categorized as either simple or complex loops. Simple loops consist of a single chromomere, while complex loops are composed of two or more chromomeres. The size and shape of the loops can vary, with some being short and thick, and others being long and thin.

4. Functions of Lampbrush Chromosomes

Lampbrush chromosomes play a significant role in the synthesis of RNA during the meiotic prophase of oocyte nuclei. They enable the oocyte to produce vast amounts of RNA that will be required for the early development of the embryo after fertilization. This high level of transcriptional activity is unique to lampbrush chromosomes compared to other types of chromosomes.

5. Location of Lampbrush Chromosomes

Lampbrush chromosomes are located within the oocyte nucleus during the meiotic prophase I in the germinal vesicle of animals, including amphibians, birds, and some mammals. They are not present in somatic cells, and their appearance is mostly limited to oocytes that are in the process of development.