Chromosome Numbers and Cell Cycle
The math of chromosomes is super important! In normal body cells, humans have 46 chromosomes. During mitosis, DNA duplicates during interphase, and then each daughter cell receives 46 chromosomes—keeping the count consistent for body cells.
In meiosis, the goal is reduction of chromosome number. You start with 46 chromosomes, but after Meiosis I, each cell has just 23 chromosomes. After Meiosis II, you still have 23 chromosomes per cell, but now in four separate cells. This half-set is exactly what's needed for reproduction!
The cell cycle consists of Interphase (G1, S, G2 phases) and cell division mitosis/meiosis+cytokinesis. Interestingly, cells spend about 90% of their time in Interphase, preparing for division, and only 10% actually dividing. Key structures involved include the centrioles, which help organize the division process, and the cytoplasm, which divides during cytokinesis.
Fun Fact: If you stretched out all the DNA from a single human cell, it would measure about 6 feet long! The incredible packaging of DNA into chromosomes is like fitting a 6-foot string into a space smaller than the period at the end of this sentence.