- During the process of growth cells divide by mitosis. Two daughter cells are formed with the same number of chromosomes as the parent cell
- At the resting stage or interphase, the strands of genetic material double while they prepare for division
- Mitosis has four stages. During the first stage (prophase), the nuclear membrane disintergrates and spindle forms and strands of chromatin condense forming chromosomes. Each chromosome is composed of two chromatids connected by a centromere. In the second stage (metaphase), the chromosomes line up in the centre of the spindle. During the third stage (anaphase), the centromeres split and the chromatids (now called chromosomes) separate and move to opposite ends of the cell. At the fourth stage (telophase), the chromosomes unwind and form strangds. The nuclear membrane re-forms and division of the cytoplasm occurs. In plant cells a new cell wall forms between the groups of chromosomes. Animal cells pinch in between the groups of chromosomes and form a new cell membrane between them.
- There is a type of cell division that halves the chromosome number. It is called meiosis and occurs in gamete formation. The gametes contain one member of each homologus pair, in contrast to body cells, which contain matched pairs of chromosomes, called homologues. In the animals, gamaetes are produced in the gonads. The typical chromosome number (diploid) is restored at fertilisation when two gametes, each with half the number of chromosomes (haploid), fuse.
- In interphase of meiosis the chromosomes replicate and therefore consist of two chromatids connected by a centromere. There are two cell divisions in meiosis. During the first prophase, the chromatin forms chromosomes, the nuclear membrane disintegrates and the spindle starts to form. In contrast to mitosis, the homologeous pairs of chromosomes, each consisting of two chomatids pair up exactly allele to allele. Portions of DNA can be exchanged between homologues during a process called crossing over. This produces essential genetics variation. During…