1. Chromosomes
Gene – segment of DNA that carries instructions for a specific trait.
DNA in cells is usually spread out so transcription can take place.
During cell division, chromosomes form.
Chromosomes are DNA and protein (histones) coiled into a rod.
After DNA replicates, two chromatids are formed that attach at a point called a centromere.

3. Each organism has a certain number of chromosomes.
 Chromosomes occur in pairs called homologous chromosomes – each is same size and has same genes.
 Diploid – 2N – cell that has two of each homologous chromosome
Human is 46
 Haploid – 1N- only 1 of a homologous pair
23 is Human

4. DIPLOID CELLS Diploid Cells = Cells with the full set of chromosomes
Paired chromosomes
Half of our chromosomes come from each parent (23 from each parent)
Somatic (non-sex) cells are diploid
Created by mitosis
Ex: Skin, Muscle, Nerve, Blood Cells

5. HAPLOID CELLS
Haploid Cells = Cells with ½ the total number of chromosomes
Gametes (sex cells) are the only haploid cells
Ex: Sperm, Egg, Pollen
Created by meiosis
Chromosome number reduced by 1/2

6. Somatic Cells - regular body cells (diploid in humans)
Gametes - cells used in sexual reproduction, these cells are haploid.
Why do gametes have only 23?
if had 46, egg and sperm would unite during fertilization and new individual would have 92
Future generations would have an impossibly large amount.

7. Cell Division – Mitosis & Cell Division 
Interphase – G1 – growth – cell doubles in size
S - synthesis – DNA Replication
G2 – growth
Mitosis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
in plants,

9. Cell Division – Mitosis & Cell Division 
Interphase – G1 – growth – cell doubles in size
S - synthesis – DNA Replication
G2 – growth
Mitosis
Prophase
 chromosomes coil
 nuclear membrane disappears
 centrioles move to opposite ends
 spindle fibers form
Metaphase
 chromosomes line up in the middle
Anaphase
 chromatids move towards opposite poles
Telophase
 nuclear membranes form
Cytokinesis
 cytoplasm splits and forms two new cells
in plants, new cell wall forms

10. Interphase

11. Prophase

12. Metaphase

13. Anaphase

14. Telophase

15. Cytokinesis

16. Crash Course: MITOSIS (11 min)
STOP POINT MITOSIS

17. form of duplication using only mitosis.
Asexual Reproduction
form of duplication using only mitosis.
produces only genetically identical offspring called clones
it is rapid, allowing for quick spread of an organism
Examples: plant cuttings, Amoeba, bacteria,
Sexual Reproduction
new individual creates by fusing two haploid cells (fertilization), creates variation
Zygote – cell created when sperm and egg unite
contains two sets of chromosomes

18. Meiosis converts a diploid cell into a haploid gamete.
Before meiosis, cell goes through Interphase, duplicating its chromosomes

19. Meiosis I
Prophase I : chromatid pairs pair up with their homologous pair, forming a tetrad.

20. Meiosis I
Prophase I : chromatid pairs pair up with their homologous pair, forming a tetrad.
Crossing over - pieces of two homologous chromosomes, switch places and end up on the other chromosome
allows for genetic diversity

21. Meiosis I Metaphase I : Tetrads line up along the center.
Independent assortment – homologous chromosomes line up randomly
Anaphase I : tetrads split and move in opposite directions.
Telophase I/Cytokinesis: Two cells form. End product of Meiosis I is two haploid (n) cells.

22. Meiosis II Prophase II : chromatid pairs move toward the center
Metaphase II : The chromatid pairs line up along the center of the cell.
Anaphase II : The chromatid pairs split moving the individual chromosomes toward the opposite poles.
Telophase II/Cytokinesis : Each of the two cells splits. All are haploid

23. The haploid cells may develop into gametes
The haploid cells may develop into gametes. In most male animals, all four cells develop into sperm. In females, one develops into an ootid, and three into polar bodies.