Biology Class 10 Cell Cycle and Cell Division

 Lesson-1    Cell Cycle and Cell Division

                       SYNOPSIS

• The sequence of events by which a cell duplicates its genome and synthesises all other cell contents and eventually divides into two daughter cells is called the cell cycle.

•Interphase involves a series of changes which take place in a newly formed cell and its nucleus

before it gets ready for division again. It is also called intermitosis. It is further divided into

✓First gap or G1 phase: Interval phase between mitosis

and the initiation of DNA replication. The cell grows

to its maximum size to prepare for DNA replication.

✓Synthetic or S phase: Synthesis or replication of DNA

occurs on the template of the existing DNA strand.

The amount of DNA per cell doubles, but there is no

change in the chromosome number of the cell.

✓Second gap or G2 phase: Synthesis of RNA and

proteins continues. Spindle protein synthesis and

aster formation take place.

Phases of Mitosis

 Phases of Meiosis

✓Meiosis-I or Heterotypic Division

✓Meiosis-II or Homotypic Division

• In this division, the two chromatids of each chromosome separate from each other and go to

separate daughter cells.

• The number of chromosomes remains the same as produced by meiosis-I.

• Meiosis-II consists of four stages—prophase-II, metaphase-II, anaphase-II and telophase-II.

• Cytokinesis follows karyokinesis of meiosis-II.

• At the end of cytokinesis, two daughter cells are formed, each with half the number of

chromosomes and half the amount of nuclear DNA of the parent cell.

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