1. DNA Replication and Chromosomes

2. DNA REPLICATION The process by which DNA makes a copy of itself This has to happen before to cell division

3. Steps in DNA Replication Step 1: Unzipping The two sides of DNA unwind and separate (unzip) Step 2: Base pairing The nitrogen bases find their match on each half of the DNA molecule

4. DNA Replication – Animations http://www.hhmi.org/biointeractive/paired-dna-strands http://www.hhmi.org/biointeractive/dna-replication-schematic Students can do this one at home: http://www.lpscience.fatcow.com/jwanamaker/animations/DNA%20Replication%20- %20long%20.html http://www.lpscience.fatcow.com/jwanamaker/animations/DNA%20Replication%20- %20long%20.html

5. Cells and Inheritance 1903: Walter Sutton studied grasshoppers Hypothesized that chromosomes were the key to understanding how offspring have traits similar to those of their parents Said that genes are carried from parents to offspring on chromosomes

6. Chromosome Pairs We receive half of our chromosomes from each parent Through sex cells: sperm and eggs All human body cell have 46 chromosomes (23 pairs) Except for sperm and egg They each have 23 chromosomes (half of original cell) Why? When a sperm fertilizes an egg, the resulting embryo has a total of 46 chromosomes

7. Meiosis Process of creating sex cells, the number of chromosomes needs to be cut in half Resulting sex cells have only half as many chromosomes as the other cells (body cells) in the organism. Each sex cell has one chromosome from each original pair.

8. Mitosis vs. Meiosis