Question

Number of chromosome groups at the equatorial plate of metaphase1 of plants having 2n = 60 chromosomes will be?
A. 60
B. 120
C. 180
D. 30

Answer 1

Hint: Meiosis is a type of cell division where a single parent cell divides twice. It produces four cells containing half of the original amount of chromosomes or genetic information. Hence it is also called the reductive cell division.

Complete Answer:
The reproductive cells undergo meiotic cell division where the parent cell divides twice to produce four daughter cells having half of the original number of chromosomes or genetic information and hence it is also called as reductive cell division. During metaphase1 of meiosis, after the spindle formation, the chromosomes arrange themselves on the equatorial plane. Hence if 2n =60 is the number of chromosomes in the equatorial plane, then the number of chromosomes will be 30.

Therefore, the correct answer is, (D) 30.

Additional information: There are two phases in meiosis. They are meiosis 1 and meiosis 2. These two phases are further divided into four substages each. So totally there are 8 stages in meiosis.
1. Meiosis 1
- Prophase 1: in this phase, the nuclear membrane or envelope breaks, the chromosomes will condens and the crossing over takes place.
- Metaphase 1: the pairs of homologous chromosomes move towards the equator and align themselves on the equatorial plane.
- Anaphase 1: homologous chromosomes split resulting in the formation of sister chromatids and then they move towards the opposite poles of the cell.
- Telophase 1 and cytokinesis: in this stage, the chromosomes are gathered at the poles and the cytoplasm divides.

2. Meiosis 2
- Prophase 2: in this phase, a new set of spindle fibres are formed around the chromosomes.
- Metaphase 2: the chromosomes align themselves at the equator.
- Anaphase 2: spindle fibers pull the chromosomes towards the pole. As a result, the centromere divides and the chromatids move toward the opposite poles.
- Telophase 2 and cytokinesis: in this stage, the cytoplasm divides as the nuclear membrane is formed around each set of chromosomes.

Note: The major difference between mitosis and meiosis 2 is that mitotic cell division occurs in a diploid cell whereas meiosis 2 occurs in a haploid cell which has half the number of chromosomes as somatic cells.