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
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
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
This is a preview of WHY SEX? -SEXUAL REPRODUCTION-TECHNICAL POINT OF VIEW FOR DISCUSSION.
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