Tag: nucleus and chromosome

The late prophase or metaphase chromosome has two similar threads or chromatids attached to each other by a narrow non stainable area called as centromere. The two parts of the chromatids on either side of centromere are called as arms. Centromeres bind to spindle fibres and help in movement of chromosomes to opposite poles.

• The kinetochore is a disc-shaped protein complex associated with the centromere of a chromosome during cell division, to which the microtubules of the spindle attach.
• It forms on a chromatid during cell division.
• Hence Kinetochore is the protein disc near the centromere.
• So, the correct answer is 'Protein disc near centromere'.

Acentric chromosomes may be lost during cell division. An acentric fragment is a segment of a chromosome that lacks a centromere. Because the centromere is the point of attachment for the mitotic apparatus, acentric fragments are not evenly distributed to the daughter cells in cell division. As a result, one of the daughters will lack the acentric fragment. Lack of the acentric fragment in one of the daughter cells may have deleterious consequences, depending on the function of the DNA in this region of the chromosome

'L' shaped chromosomes that appear during anaphase are sub-metacentric. According to the position of the centromere, the metacentric chromosomes are X shaped and due to the unequal length of the arms of the chromosomes, they become L shaped and are called sub-metacentric.

The arm ratio in metacentric condition is 1:1. These are X-shaped chromosomes, with the centromere in the middle, so that, the two arms of the chromosomes are almost equal. A chromosome is metacentric, if its two arms are roughly equal in length. In a normal human karyotype, two chromosomes are considered metacentric: chromosomes 1 and 3. In some cases, a metacentric chromosome is formed by balanced translocation: the fusion of two acrocentric chromosomes to form one metacentric chromosome.

Chromosome with centromere at one end is telocentric. A telocentric chromosome's centromere is located at the terminal end of the chromosome. Telomeres may extend from both ends of the chromosome. Humans do not possess telocentric chromosomes.

A chromosome present in addition to the normal chromosome complement is called as a supernumerary chromosome, also known as accessory chromosome. These chromosome does not produce any detectable phenotypic expression in an organism. These chromosomes are not essential for the life of a species, and are lacking in some (usually most) of the individuals. Thus a population would consist of individuals with 0, 1, 2, 3 (etc.) supernumeraries.

The rod-like chromosomes which have the centromere on the proximal end are known as the telocentric chromosomes. Humans do not possess telocentric chromosomes but they are found in other species such as mice. Thus, the correct answer is option A.