1. Meiosis
Chapter 10.1 and 11.3

2. Do Now
How is a baby made?
On the cellular level, draw how a baby is made. (NO PHALLIC SYMBOLS PLEASE!)

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. Karyotype

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

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

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

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

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

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

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

22. Telophase I The spindles break down.
Chromosomes uncoil and form two nuclei.
The cell divides.

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

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

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

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

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

28. 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.

29. Genetic Variability Animation

30. Do Now: Label the phases of meiosis

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

32. Think – Pair - Share
Draw out the stages of meiosis using the following cell. Make sure you draw the cell with crossing over of only one pair of homologous chromosomes! (use colored pencils)

33. Do Now: Label the phases of meiosis

34. Do Now A. Prophase I 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

37. Review
How does meiosis promote genetic variability? List 3 reasons why.

38. Review Spermatogenesis and oogenesis

39. Do Now
If a hamster has 44 chromosomes in G1 phase of the cell cycle, then…
How many chromatids are in G2 Phase?
How many chromosomes are in the G2 Phase?
How many chromosomes will be in each cell after it has gone through mitosis?

40. Do Now What two divisions do your cells undergo?
What are the differences between the two?

45. Animations on Meiosis