Cells and Molecules - Brutes or Angels: Human Possibility in the Age of Biotechnology - page 20

fig. 1.9. life cycle of humans and other sexually reproducing organisms. The fertilized
egg and the cells arising from it by mitosis are diploid, having two copies of each type
of chromosome. meiosis produces haploid eggs and sperm with just one copy of each
type of chromosome. Union of egg and sperm regenerates the diploid state, allowing
the next generation of individuals to grow via mitosis.
Cell Division and the Chain of life
There is an unbroken chain of life, linked by DnA replication and cell di-
vision, from the first cells some 3.8 billion years ago to us. All life forms
come from ancestral life forms, and all cells come from pre-existing cells.
These foundational principles of biology depend upon the replication of
genetic material and cell division. here we examine two distinct types of
cell division in eukaryotic cells: mitosis and meiosis. Appreciating the differ-
ences between mitosis and meiosis is important for understanding certain
biotechnologies, particularly stem cell technologies (chapter 2) and clon-
ing (chapter 7).
mitosis produces two new cells genetically identical to the parent cell,
whereas meiosis produces cells with half the genetic content of the parent
cell (fig. 1.9). Through mitosis, fertilized single eggs give rise to the tril-
lions of cells in multicelled organisms like human beings and giant red-