Journey Through The Cell

1. A prokaryotic genome is often a single long DNA molecule; eukaryotic genomes usually consist of several such molecules. A typical human cell has 3 meters of DNA. Before a cell can divide all of said DNA, it must be coiled and then apportioned to give each daughter cell a complete genome.
2. The replication and distribution of so much DNA is done because the DNA molecules are packaged into chromosomes. Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus. Reproductive cells, or gametes—sperm cells and egg cells—have half as many chromosomes as somatic cells (all body cells save gametes), or 23 chromosomes in humans.
3. In each generation of humans, meiosis reduces the chromosome number from 46 to 23. Fertilization joins gametes and doubles the chromosome number to 46 again and mitosis conserves that number in every somatic cell of the new individual. The role of meiosis in reproduction and inheritance will be discussed later on.
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