Test: Nucleus & Chromosomes (May 20) - NEET MCQ

Secondary constriction II of chromosome is generally concerned with the synthesis of rRNA. Secondary constriction is seen at the chromosome in addition to primary constriction or centromere. Chromosome can bend only at the site of primary constriction during anaphase.

The chromosome that remains condensed during interphase is X chromosome of Barr body. A Barr body is the inactive X chromosome in a female somatic cell, rendered inactive in a process called lyonization. In humans with more than one X chromosome, the number of Barr bodies visible at interphase is always one less than the total number of X chromosomes. 

Dr. Hammerling began acetabularia in laboratories in 1930.He determine the nucleus control the development of organisms by containing hereditary information or DNA from his grafting experimentation on the Green algae.

Diplotene chromosomes are the lampbrush chromosomes. Lampbrush chromosomes are a special form of chromosome found in the growing oocytes (immature eggs) of most animals, except mammals. Chromosomes transform into the lampbrush form during the diplotene stage of meiotic prophase I due to an active transcription of many genes. They are highly extended meiotic half-bivalents, each consisting of 2 sister chromatids.

A swelling in the band of a polytene chromosome is an indication of gene action. Polytene chromosomes are very large chromosomes. These are developed from the specialized cells which undergo many rounds of DNA replication without cell division forming a giant polytene chromosome. Polytene chromosomes are formed when replication produce many sister chromatids that remain synapsed together. Polytene cells have multiple copies of genes permits a high level of gene expression. 

Thus, the correct answer is option A. 

A nucleoside triphosphate (NTP) is a molecule containing a nucleotide bound to three phosphates. These NTPs include ATP, GTP, CTP, UTP. They generally provide energy and the phosphate group for phosphorylation. They are stored in the nucleus.
Thus, the correct answer is option (D), 'CTP and all the above'.

• Nucleus Structure:




• The nucleus is a two-layered structure consisting of the nuclear envelope and nucleoplasm.




• Nuclear Envelope:




• It consists of two membranes - the inner and outer nuclear membranes.


• These membranes enclose the nucleus and separate its contents from the cytoplasm.




• Nucleoplasm:




• It is a gel-like substance within the nucleus that contains chromatin (DNA and proteins).


• Various nuclear bodies and organelles are found in the nucleoplasm.




• Function of the Nucleus:




• The nucleus serves as the control center of the cell, containing the cell's genetic material and regulating gene expression.


• It is responsible for cell growth, metabolism, and reproduction.

In human being secondary constriction II found on Acrocentric chromosomes. It have a centromere which is severely offset from the center leading to one very long and one very short section. Human chromosomes 13,15, 21, and 22 are acrocentric.

Chromosomes can be defined as thread-like structure which contains DNA and proteins which are found in the nucleus of most living cells.

They carry the genetic information in the form of genes.

The word chromosome is derived from the Greek word chroma meaning "colour" and soma meaning "body".

The term was coined by von Waldeyer-Hartz in relation to the term chromatin which was introduced by Walther Flemming.

So, the correct answer is 'Waldeyer'.

Nucleus of a cell was discovered by Scottish botanist Robert Brown in 1831. The presence of a nucleus in an atom was discovered and proved by Nobel Laureate Dr. Ernest Rutherford through his gold leaf scattering experiment.