Q.85 Which one of the following statements is NOT correct?
(A) During metaphase, the 2 copies of chromosomal DNA are held together at the centromere
(B) The short arm of chromosomes is referred to as 𝑝 and the long arm is referred to as 𝑞
(C) The terminal structures at the end of the chromatids are referred to as telomeres
(D) The terms heterochromatin and euchromatin refer to the active and repressed regions of the
chromosome respectively

During metaphase of mitosis, chromosomes align at the cell’s equator with sister chromatids held together, but one option misstates this process. This MCQ tests core knowledge of chromosome anatomy and cell division stages.

Correct Answer

Option (A) is NOT correct. The two copies of chromosomal DNA (sister chromatids) remain held together at the centromere during metaphase and only separate in anaphase.

Option (A) Explanation

In metaphase, replicated chromosomes condense and line up at the metaphase plate, with sister chromatids joined at the centromere where spindle fibers attach. Separation of these chromatids occurs later in anaphase when cohesin proteins degrade, pulling them to opposite poles. This statement wrongly implies separation happens in metaphase.

Option (B) Explanation

Chromosomes have a short arm denoted as p (from petite) and a long arm as q (from queue or French for tail). The centromere divides the chromosome into these arms, a standard cytogenetic notation used in karyotyping.

Option (C) Explanation

Telomeres are repetitive DNA sequences (e.g., TTAGGG in humans) with protective proteins at the ends of chromatids, preventing end-to-end fusion and degradation. They shorten with each cell division, linking to aging and cancer.

Option (D) Explanation

Euchromatin represents transcriptionally active, loosely packed regions allowing gene expression, while heterochromatin is densely packed and repressed, silencing genes. Constitutive heterochromatin stays condensed (e.g., centromeres), and facultative can switch states.