Interphase is of the longest duration. It has following events and is divided in the following phases

(a) $G_1$ phase (Gap 1) Corresponds to the interval between mitosis and initiation of DNA replication. Cell is metabolically active and continuously grows but does not replicate its DNA.

(b) S-phase (Synthesis phase) Marks the period during which DNA synthesis or replication takes place.

(i) Amount of DNA per cell doubles.

(ii) No increase in chromosome number.

(c) $\mathrm{G}_2$ Phase (Gap 2) Proteins are synthesised for the preparation of cell division, while cell growth continues.

Acetocarmine and Giemsa stain can be used to stain the chromosomes.

Meiosis is a special kind of cell division, also called as reduction division, which occurs in germ cells or sex cells of male and female reproductive organs of plants and animals. They produce male

and female gametes that take part in sexual reproduction.

1 hour 20 minutes

These are the 4 subsequent cell divisions to produce 16 cells and each division takes $=20 \mathrm{~min}$ Total time $=20 \times 4=80$ minutes or 1 hr 20 minutes

So, 1 cell produces 16 cells in 1 hour 20 minutes and 2 cells produces 32 cells in 1 hour 20 minutes.

All the cells in the human body are somatic cells except germinal cells in the male and female reproductive organs. The somatic cells divide by mitotic cell division for growth and regeneration. These can be used to demonstrate mitosis.