1. HOW CELLS ARE MADE
Chapter 4

2. Cell Divison
Each somatic cell has 46 chromosomes (half from mother, half from father)
Remember, mitosis replicates somatic cells and meiosis replicates gametes
Gametes don’t divide: only somatic cells do
Also remember when cell division begins, the DNA replicates itself. This results in the chromosomes condensing and becoming visible.

3. Remember…
What is always the first step in cell divison?

4. Remember… What is always the first step in cell divison?
DNA Replication!

5. Mitosis Begins immediately after fertilization
Embryo continues dividing into identical cells that eventually become specialized
Mitosis continues during life, for growth and healing
Mitosis begins with somatic cells that have 46 chromosomes and the end result is 2 identical diploid daughter cells, each with 46 chromosomes and a complete DNA blueprint
Several stages, outlined on pages 66

7. Meiosis Comes from the Greek meaning to reduce Production of gametes
End results is production of haploid gametes (with 23 chromosomes) that carry genetic info and introduce variability
Primary oocytes are specific cells that produce egg cells and primary spermatocytes produce sperm cells

8. Meiosis There are 2 meiotic divisions
Meiosis I reduces the number of chromosomes from 46 in the parent cell to 23 in the daughter cells
Meiosis II pulls chromatids apart and pinches into new cells
Most important thing to remember is the end result of each part of the process, as well as that chromosomes will “reshuffle,” or exchange pieces to ensure variability

9. Meiosis
Look at pages 68-69

10. Key Points Focus on: Where the chromosomes originally came from
What happens to those maternally and paternally derived chromosomes during this process
How many chromosomes are present in the parent and daughter cells after meiosis

11. Chromosomal Aberrations
More about chromosomal mutations
Common cause is failure of chromosomes to separate property during cell division
Separation of chromosomes during anaphase is disjunction; failure to separate correctly is nondisjunction
If nondisjunction occurs, all cells will have the wrong number of chromosomes

12. Assignment Mitosis and Meiosis WS in groups Lab 4.1 #3 and 4
Self-Test 4.1
On the self-test, the first circles are cells that have already had DNA replication