Question

In two spindle bodies in metaphase II, chromosome at equator have .......... and ..................

• A. One chromatid and one centromere.
• B. Two chromatids and two centromeres.
• C. Two chromatid and one centromere.
• D. One chromatid and two centromeres.

Answer 1

The correct option is C Two chromatid and one centromere.

Homologous chromosomes pair during prophase stage of meiosis I. In the prophase stage of meiosis I, when homologous chromosomes pair, structures called as bivalents are produced which comprise of two homologous chromosomes each. Each chromosome of each bivalent structure, in turn comprises of two sister chromatids joined at the centromere. Thus, each bivalent is actually a tetrad of chromatids - two sister and two non-sister chromatids. Two chromatids joined together at the centromere are called sister chromatids and two chromatids which are not joined at the centromere, nevertheless are a part of same bivalent are called non-sister chromatids. Next event after pairing is crossing over after which homologous chromosomes separate and move to opposite poles. In this manner in meiosis I, there is no splitting of centromere. In the next division meiosis II, at the metaphase stage only a single chromosome is arranged at the equator, its other homologue has passed on to another pole and will undergo a similar division there. In metaphase stage of second division, the chromosomes at the equator will comprise of two sister chromatids joined at the centromere. The centromere will split in metaphase II and two chromatids shall migrate to opposite poles.