Question

The chromosome in which centromere is situated close to one end are
A. Metacentric
B. Acrocentric
C. Telocentric
D. Sub- metacentric

Answer 1

The centromere is the region of the chromosome that links the sister chromatids and also allows the attachment of spindle fibers through a kinetochore and signals the next phase of the cell cycle. There are 23 pairs of chromosomes in humans and every chromosome has a different shape based on the position of the centromere.

Complete answer: There are four shapes based on the situation of the centromere are as follows-
I. Acrocentric chromosomes: In acrocentric chromosomes, the centromere is located close to the p arm. The p arm looks very small but is present. Acrocentric chromosomes form an ‘i’ shape. Acrocentric chromosomes are located around the nucleolus and due to less chromosome density, they are prone to translocations and can cause defects at times like aneuploidy and cancer. The six out of 23 chromosomes that are acrocentric are chromosome 13, chromosome 14, chromosome 15, chromosome 21, chromosome 22, and a Y chromosome.
II. Metacentric chromosomes: Chromosomes have two arms: ‘p’ arm which is a short arm and ‘q’ arm which is a long arm from the centromere. The metacentric chromosome is an ‘M’ shaped chromosome. The centromere is located exactly in the middle of the p and q arms and the arms look of equal length. The five out of 23 chromosomes that are metacentric type are chromosome 1, chromosome 3, chromosome 16, chromosome 19, and chromosome 20.
III. Telocentric chromosomes: In the telocentric chromosome, the centromere is located at one end of the arm and thus it has only one arm. Telocentric chromosomes are not present in humans.
IV. Sub-metacentric chromosomes: In the sub-metacentric chromosome, the centromere is located as such that p arm and q arm are in unequal length. It forms an ‘L’ shape. Chromosomes number 2, 4, 5, 6, 7, 8, 9, 10, 11, 12, 17, 18, and X chromosome are sub-metacentric chromosomes in humans.
Hence, the correct answer is option (B).

Note: The chromosome types are classified based on the position of the centromere in the anaphase. Karyotyping is used to see the position, size, and shape of the chromosome. Y, M, L, such types of shapes are found in chromosomes.