1. Do Now!! 
How many chromosomes are in human non-sex cells? How about human sex cells?
Where do we get those chromosomes from??

2. Meiosis!!
Chapter 10

3. Meiosis Purpose: to make sex cells Male gamete= sperm
Gamete: sex cell
Male gamete= sperm
Female gamete= egg (ovum)

4. Let’s define the following words…
Meiosis:
Sexual reproduction- production of gametes
Gamete:
Sex Cells (egg and sperm)
Derived from germ cells
Somatic Cells:
Body Cells (non-sex cells)

5. Haploid: Diploid: Fertilization: Zygote:
Half the chromosome number (n)
Cells with 1 of each pair of chromosomes (23)
Ex: Gametes
Diploid:
2 of each type of chromosome (2n)
Cells with twice the haploid number (46)
Ex: Somatic cells
Fertilization:
Sperm enters egg
Zygote:
Fertilized egg (diploid)

6. Chromosomes and Chromosome Number
Homologous chromosomes —set of chromosomes with same genes in same locations:
Get one from each parent
Same length
Somatic cells: 46 chromosomes
Gametes: 23 chromosomes

8. Karyotype Organized profile of a person’s chromosomes
Autosomes (non-sex chromosomes): #’s 1-22
Sex chromosomes: #23
Monosomy: missing one chromosome
Trisomy: 3 copies instead of 2

10. Do Now!! 
If an organism is 2n=46, how many chromosomes are in the sex cells?
What is monosomy? Trisomy?
Define homologous chromosomes.

11. somatic cells (2n)
gametes (n)

12. Meiosis Produces 4 daughter cells (NOT genetically identical!!!!!!)
Like mitosis (PMAT), but 2 divisions:
Meiosis I (separation of homologous chromosomes)
Meiosis II (separation of sister chromatids)
Produces 4 daughter cells (NOT genetically identical!!!!!!)

13. Interphase Same as Mitosis (G1, S, G2) DNA- Chromatin
Centrioles- located near the nucleus
Nucleolus is present

14. Prophase I
Pairing of homologous chromosomes occurs forming a tetrad (Synapsis)
The nuclear envelope breaks down/nucleolus gone
Spindles form
Crossing over takes place

15. Crossing over Homologous chromosomes exchange genetic material
Recombination of genes between chromosomes
How is crossing over related to genetic variation?

16. Metaphase I Chromosome centromeres attach to spindle fibers
Homologous chromosomes line up at the equator

17. Anaphase I
Homologous chromosomes separate and move to opposite poles

18. Telophase I The spindles break down
Chromosomes uncoil, 2 new nuclei form
The cell divides

19. Prophase II A second set of phases begins Chromosomes condense again
Spindles form in each new cell

20. Metaphase II
Chromosomes line up at metaphase plate of each cell

21. Anaphase II
The sister chromatids are pulled apart at the centromere by spindle fibers
Move toward the opposite poles of the cell

22. Telophase II
The chromosomes reach the poles and the nuclear membrane and nuclei reform
Spindles break down

23. Cytokinesis Cytokinesis results in four haploid cells (gametes)
Each with n number of chromosomes.
*So… if the original diploid cell has 10 chromosomes, how many will each gamete have?
*Why are the gametes NOT genetically identical?

26. Do Now!! 
Match the description to the phase of meiosis.
1. Sister chromatids are pulled apart. _____
A. Prophase I
2. Homologous chromosomes line up in the middle of the cell._____
B. Metaphase I
3. 2 daughter cells are formed ____
C. Telophase I
4. Nuclear membrane disappears__
D. Anaphase II
5. Nuclear membrane reforms around 4 cells ____
E. Anaphase I
6. Homologous chromosomes are pulled apart ____
F. Telophase II

27. Crash course biology!!

28. Spermatogenesis vs oogenesis

29. Genetic Variability
Depending on how the chromosomes line up at the equator, four gametes with four different combinations of chromosomes can result.
Genetic variation also is produced during crossing over and during fertilization, when gametes randomly combine.

30. Label the phases of meiosis