Cell Division

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All cells come from prexisting cells and since living things are made from cells, understanding how cells divide and the different types of cell division is fundamental to understanding how multicellular organisms such as humans reproduce, grow and maintain themselves.

Here we will examine cell division in prokaryotes and two types of cell division important in eukaryptes: mitosis and meiosis.

This image shows an onion root tip cell(left of arrow)during metaphase of mitosis. The blue black structures are chromosomes lined up in the center of the cell.

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Cell Division: An Introduction

As cell theory developed scientists noticed that there seem to be two types of cell division in eukaryotes.

Mitosis: In mitosis, two daughter cells are typically produced from an original parent cell and the two daughter cells have the same number of chromosomes as the original parent cell. Chromosomes (2) contain the DNA that makes up the genetic material of a cell. Mitosis occurrs in most of the cells of your body for growth, repair and replacement of damaged cells. The chromosome number of the daughter cells is the same as for the parent cell. In animals the organism's cells are typically diploid and daughter cells produced by mitosis will be diploid. In addition the daughter cells will be genetically identical to the parent cell.

Meiosis: In meiosis, four haploid daughter cells are typically produced. The daughter cells have half the number of chromosomes as the original parent cell. Also in meiosis, the cells produced by meiosis become what in animals are called sex cells or gametes. The male gamete is the sperm, the female gamete the ovum or egg. When the two gametes get together the resulting cell is called a zygote. Meiosis occurrs, not in the cells of your body as a whole, but in specialized cells in your reproductive organs.

Another thing that became clear is that the patterns of cell division and gamete formation differ among the three major kingdoms of multicellular organisms: the Fungi, Plantae and the Animalia. We will conclude our look at cell division by looking at cell division in the context of these kingdom's basic life cycles.

Summary of Mitosis and Meiosis in Animals.

Mitosis

Daughter cells

Meiosis

Daughter cells

Type of cells produced Somatic cells Gametes
Function of cells Growth/repair

Asexual reproduction

Sexual reproduction
Chromosome

number

Same as parent cell Reduce to haploid
Genetic material Identical to parent cell Half of genetic material and in new gene comibinations. Gametes not identica to either parent cell of each other.

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pgd created 1/10/00 revised 08/15/02