1. Do Now Please hand your homework in the bin.
Then Answer in your notebooks:
How do we get half of our DNA from each parent, and still only have 46 chromosomes?

2. Meiosis
Chapter 10.1 and 11.3

3. Why does sex exist?
Sexual reproduction creates genetic variability

4. Let’s Brainstorm…
How do we get our different traits?

5. What is the difference between fraternal and identical twins?

6. Let’s define the following words…
Meiosis:
Sexual reproduction-production of gametes
Gamete:
Sex Cells (egg and sperm) haploid
Somatic Cells:
Body Cells - diploid

7. Haploid: Diploid: Fertilization: Zygote:
Half the chromosome number (n)
1 of each pair of chromosomes (23)
Diploid:
2 of each type of chromosome (2n)
Twice the haploid number
Fertilization:
Sperm enters egg
Zygote:
Fertilized egg (diploid)

8. Chromosomes and Chromosome Number
Human body cells have 46 chromosomes
Each parent contributes 23 chromosomes
Homologous chromosomes —one of two paired chromosomes, one from each parent

9. Homologous pair of chromosomes
Centromere
Figure 8.12 A homologous pair of chromosomes.
This figure shows a pair of homologous chromosomes in their duplicated state. Each homologue is represented as a pair of chromatids. These two contexts for the word pair often confuse students. It would be helpful to introduce the term tetrad at this point, to emphasize both uses of the term pair.
Sister chromatids
One duplicated
chromosome *

10. Homologous Chromosomes
Same length
Same centromere position
Carry genes that control the same inherited traits

11. Karyotype

12. Meiosis The sexual life cycle in animals involves meiosis
Meiosis produces gametes.
When gametes combine in fertilization, the number of chromosomes is restored.

14. Cell Cycle Prepare Growth Division 2N 2N Mitosis Meiosis 2N N
DNA Replication
Prepare
Growth
Division 2N 2N
Mitosis
Meiosis 2N N

15. Do Now
Label A, B, and C
(Hint same size, same shape…)

16. Do Now Please put phones on my desk.
Grab the worksheet, and a marker. Complete both sides
No Notes, or partners.
Yay BIO!! 

17. Meiosis 2 Divisions Meiosis I (separation of homologous chromosomes)
Meiosis II (separation of sister chromatids)

18. Interphase Same as Mitosis (G1, S, G2) DNA- Chromatin
Centrioles- located near the nucleus

19. Prophase I Pairing of homologous chromosomes occurs. (Synapsis)
Each chromosome consists of two chromatids.
The nuclear envelope breaks down.
Spindles form

20. Prophase I (cont.)
Crossing over produces exchange of genetic information.
Crossing over —chromosomal segments are exchanged between a pair of homologous chromosomes.

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

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

23. Telophase I/Cytokinesis
The spindles break down.
Chromosomes uncoil and form two nuclei.
The cell divides into two haploid cells

24. Prophase II
A second set of phases begins as the spindle apparatus forms and the chromosomes condense.

25. Metaphase II A haploid number of chromosomes line of at the equator
Sister chromatids line up

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

27. Telophase II
The chromosomes reach the poles, and the nuclear membrane and nuclei reform.

28. Cytokinesis Cytokinesis results in four haploid cells
Each with n number of chromosomes.

30. Do Now Phones on my desk, and take out your homework.
Then please grab the worksheet off my desk, and begin working on it (only the mitosis vs. meiosis side)

32. Genetic Variability
Depending on how the chromosomes line up at the equator during Metaphase I, four gametes with four different combinations of chromosomes can result. (Independent Assortment)
Genetic variation also is produced during:
crossing over (during Prophase I)
Fertilization (when gametes randomly combine)

33. Review Spermatogenesis and Oogenesis

34. Genetic Variability Animation

35. Do Now: Label the phases of meiosis

36. Do Now – Period 3 How many autosomes? How many sex chromosomes?
What is the sex of this patient?
Monosomy, Trisomy?
Is this individual normal?

37. Do Now Match the description to the phase of meiosis. A. Prophase I
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