Question

A chromosome with a centromere near the middle is known as
a. Metacentric
b. Submetacentric
c. Acrocentric
d. Telocentric

Answer 1

Chromosomes are present in the nucleus, thread-like structures, which carries genetic information from one generation to another. A centromere is a constricted region of DNA or a structure in a chromosome, which plays an essential role in the segregation of chromosomes during the process of the cell cycle in eukaryotic cells.

Complete answer:
Centromeres are the compressed region or a part of elongated chromosomes. It is the specialized DNA sequence in the chromosomes. It links or holds together the pair of sister chromatids. The centromeres are involved in separating the chromosome into a short arm and a long arm.
Centromeres are not located exactly in the center but at the end of chromosomes. This organelle is also called as the chromosome’s arms as they are present on either side of the centromere.

• Telocentric chromosome:
It is a rod-like chromosome with centromere present on the proximal end. No ‘p’ arm (short arm) present. Telomeric chromosomes are not found in humans

• Acrocentric chromosome:
It is a rod-like, centromere present at one end giving rise to one very short arm and an exceptionally long arm

• Submetacentric chromosome:
It is an L-shaped or J-shaped, with a centromere near the middle of the chromosome giving rise to two unequal arms.

• Metacentric chromosome:
It is a X-shaped chromosome with a centromere at the center of the chromosome giving rise to two equal arms. The chromosomes are almost equal in length. In a normal human karyotype, five chromosomes are metacentric: chromosomes 1, 3, 16, 19, and 20.

Hence, the correct answer is option (B).

Note: Metacentric chromosomes are those who have centromere in the middle of the chromosome with two equal arms of the chromosomes. A chromosome is considered as metacentric if its two arms are roughly equal in length. Five chromosomes are considered metacentric, in a normal human karyotype.