Tag Archives: Cell division


Reasons for Cell Division

  • Cell division is required for:
    • a) growth
    • b) repair & replacement of damaged parts
    • c) reproduction of the species

In Cell Division Copies of the DNA Must Be Sent to Both New Cells

  • Since the instructions for making cell parts are encoded in the DNA, each new cell must get a complete set of the DNA molecules
  • This requires that the DNA be copied (replicated, duplicated) before cell division

Genetic Blueprints for Cells Are Organized Into Chromosomes

  • The plans for making cells are coded in DNA

Cells: Structure & Function

All Living Organisms are Made Up of Units Called Cells

  • Cell theory:
    • All living creatures are made from 1 or more cells
    • All cells are produced from previously existing cells (no spontaneous generation)
  • All cells appear to be descended from the first cell which existed about 4 billion years ago
  • For a species to exist its reproductive cells must be potentially immortal (no aging)
  • Our bodies start from a single cell and contain about 100,000,000,000,000 (10^13) cells at maturity

There Are 2 Basic Types of Cells: Prokaryotic and Eukaryotic


The sexual cycle
Image via Wikipedia

Sex is Very Costly

  • Large amounts of energy required to find a mate and do the mating: specialized structures and behavior required
  • Intimate contact provides route for infection by parasites (AIDS, syphillis, etc.)
  • Genetic costs: in sex you pass on only half your genes to your children
  • Males are an expensive luxury- in most species they contribute little to rearing offspring

But There are Some Advantages

  • More genetic diversity: more potential for survival of species when environmental conditions change
    • Shuffling of genes in meiosis
    • Crossing-over in meiosis