1. B C A E D F Monday, 12/4/17 Correct Order: E, A, C, D, B, F Telophase
Metaphase
Prophase B C A
Interphase
Anaphase E
Cytokinesis D F

2. Today & Homework Today: 1.) Turn in your Chapter 8 Outline (finally)
2.) Meiosis Notes
Homework: 1.) PRINT a copy of “Meiosis Flipbook Instructions & Template” for your lab
activity on BLOCK DAYS (will be posted tonight under “Class Assignments,
Chapter 8”)
2.) Flipbook will be due on MONDAY, 12/11, which is also the day you will
have a Mitosis/Meiosis Quiz

3. Word of the Day Intersperse (verb)
To scatter here or there or place at intervals among other things
“Red flowers are interspersed throughout the lawn.”

4. Reminder…
The DNA is NOT copied during Prophase. It has been copied in INTERPHASE (specifically, during the Synthesis stage). During Prophase, the replicated chromatin is just condensed (coiled tightly) into chromosomes.

5. Important Vocabulary
Homologous Chromosomes: Chromosomes of the same type; for example, you have two copies of Chromosome 6…one from mom, one from dad. Homologous chromosomes have the same genes in the same location, but the VERSIONS (alleles) of the genes may be different. Maybe Chromosome 6 from mom has an allele for blue-eyes, but the one from dad has an allele for brown-eyes. Same gene (eye color), but different versions (blue vs. brown).
Non-Homologous Chromosomes: Chromosomes that are NOT the same type; for example, X and Y; Chromosome 1 and Chromosome 6, etc. Different genes.
Spermatogenesis: The production of sperm by the process of meiosis
Oogenesis: The production of ova (eggs) by the process of meiosis
Germ Cells: Sex cells (only egg and sperm)
Somatic Cells: Any body cell that is NOT a sex cell (skin, kidney, liver, heart, etc.)

6. Chromosome Characteristics
Diploid set for humans; 2n=46. “n” represents chromosome number. n = 23, but in our body (somatic) cells it is 2 x 23 = 46.
Autosomes = non sex-chromosomes; one from each parent (humans=22 pairs of 2).
Sex chromosomes (humans have 1 set; mom only gives an X, dad can give X or Y, which determines baby’s sex).
Female-sex chromosomes are homologous (XX).
Male-sex chromosomes are non-homologous (XY).

7. Meiosis in Overview
Produces four genetically different, haploid (n = 23) reproductive cells
Two cell divisions; eight steps
Reduces the number of chromosomes by half
When gametes unite during fertilization, the normal diploid (2n) number is restored
In testes- spermatogenesis  sperm
In ovaries – oogenesis  ova (egg cells)

8. Crossing-Over

10. Prophase I Each chromosome condenses, then pairs with its homologue
Spindle fibers appear
Nucleolus and nuclear membrane disassemble
CROSSING-OVER results in exchange of genetic material between homologous chromosomes – genetic recombination!!
Combined pairs of homologous chromosomes is called a tetrad
Pretend this is just chromosome #1. You have two of them…one red strand from mom, and one blue strand from dad. Each chromosome replicates and forms a sister chromatid, so now you have four total chromosomes. They come together to swap genetic info.

11. *You must know that CROSSING-OVER occurs in PROPHASE I of MEIOSIS
Remember, we have two copies of each chromosome; one from mom, one from dad
Each of those chromosomes replicates to form a sister chromatid, giving you four chromosomes
They form a tetrad, and crossing-over occurs. This gives GENETIC VARIATION.
Imagine that the cell on the right is a human cell and has 46 chromosomes, each of which replicates and creates sister chromatids. So there are 92 chromosomes total.

12. Metaphase I
Spindle fibers from one pole attach to the centromere of one homologous chromosome; spindle fibers from the opposite pole attach to the other homologous chromosome of the pair.
Homologues align randomly at spindle equator.
Equator (middle) of the cell
Kinetochore fibers
# of chromosomes = 92

13. Anaphase I
Each homologue is separated from its partner and moved to opposite poles of the cell
Random separation of the homologous chromosomes is called INDEPENDENT ASSORTMENT and results in GENETIC VARIATION (just like crossing-over)
**So far, TWO ways for genetic variation to occur:**
1.) Crossing-over during Prophase I
2.) Independent assortment during Anaphase I (due to random alignment during Metaphase I)
# of chromosomes = 92

14. Telophase I and Cytokinesis I
Homologous chromosomes are separated from each other and at opposite ends of the cell (Telophase I)
Sister chromatids are still attached to each other
During Cytokinesis I, the one original cell splits into two cells
# of chromosomes = 46
# of chromosomes = 46

15. Between Cytokinesis I and Prophase II, there is no DNA replication
This is the end result of Cytokinesis I of Meiosis I, and also the starting material for Prophase II of Meiosis II.
Two cells, each with 46 chromosomes
Homologous chromosomes were separated, but sister chromatids are still together
GENETICALLY DIFFERENT from EACH OTHER and the ORIGINAL CELL
# of chromosomes = 46
# of chromosomes = 46

16. Prophase II There is no DNA replication prior to Prophase II
Sister chromatids of each chromosome are still attached at the centromere
# of chromosomes = 46
# of chromosomes = 46

17. Metaphase II
Sister chromatids are aligned along the equator and attached to the kinetochore fibers
Again, alignment is RANDOM
# of chromosomes = 46
# of chromosomes = 46

18. Anaphase II
Sister chromatids in each of the two cells split apart and go to opposite poles of the cell
Since sister chromatids are now separated, the genetic information is now chromosomes
# of chromosomes = 46
# of chromosomes = 46

19. Telophase II and Cytokinesis II
# of chromosomes = 46
# of chromosomes = 23
In telophase, chromosomes start to decondense back into chromatin, then the cells finally split during cytokinesis. This makes FOUR haploid cells, each of which contain 23 chromosomes
# of chromosomes = 23
Genetically DIFFERENT from EACH OTHER and the ORIGINAL CELL
# of chromosomes = 23
# of chromosomes = 46
# of chromosomes = 23

20. Mitosis vs. Meiosis

21. Two genetically identical diploid (2n) cells
Mitosis
Four genetically different haploid (n) cells
Meiosis

22. Meiosis Summary & Key Points
Purpose: To create sex cells (egg and sperm) by reducing the number of chromosomes by HALF
Sex cells are HAPLOID; in humans, they only contain 23 chromosomes
Egg cell (23 chromosomes) + Sperm cell (23 chromosomes) = Zygote (46 chromosomes)
Allows for GENETIC VARIATION (unlike mitosis)
Crossing-Over during Prophase I
Independent Assortment during Anaphase I and II…due to random alignment along the equator