1. MEIOSIS
Making gametes…

2. ASEXUAL REPRODUCTION
Produces cells that are IDENTICAL copies of parent cell; can’t adapt/change EX: Binary fission, budding & regeneration
Planaria animation:

3. SEXUAL REPRODUCTION
Family image from:
Combines genetic material from sperm & egg; offspring are
genetically different

4. ADVANTAGES OF SEXUAL REPRODUCTION
Allows for variation in population
Allow species adapt to
changes in
their environment

5. Think-Pair-Share
Human body cells contain 46 chromosomes 1. How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis?

6. Think-Pair-Share
2. If a sperm containing 46 chromosomes fused with an egg containing 46 chromosomes, how many chromosomes would the resulting fertilized egg contain? Do you think this would create any problems in the developing embryo?

8. Think-Pair-Share
3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have?

10. DIPLOID VS HAPLOID
Body cells (somatic cells) have 2 copies of each chromosome = DIPLOID (2n) (one from mom; one from dad)

11. DIPLOID & HAPLOID Sex cells have only one copy of each chromosome =
All sperm and egg cells
are haploid
HAPLOID
(1n)

12. MITOSIS CREATES DIPLOID BODY CELLS
Makes 2 cells genetically identical to parent cell & to each other
Used by organisms to: grow, repair injuries, replace cells

13. MEIOSIS CREATES HAPLOID SEX CELLS
Makes 4 cells genetically different from parent cell & from each other
Used for sexual reproduction

14. HOMOLOGOUS CHROMOSOMES
SAME SIZE & SHAPE
CARRY GENES for the SAME TRAITS
BUT NOT IDENTICAL!

15. Stages of Meiosis

16. Meiosis

17. Meiosis takes place in two series of steps
Meiosis I I, P, M, A, T +
Meiosis II P, M, A, T
Which means…no DNA replication before meiosis II
No second “I”

18. Interphase I
DNA replicates creating homologous chromosomes

19. PROPHASE I Homologous chromosomes pair up = SYNAPSIS
TETRAD = group of FOUR (4)
chromatids
Images modified from:

20. Exchange of DNA between homologous pairs
2. CROSSING OVER
Exchange of DNA between homologous pairs
After crossing over, chromatid arms are NOT IDENTICAL anymore

21. Metaphase I
Tetrads line up in the middle

22. Anaphase I- Tetrads pull apart to opposite ends of the cell.

23. Telophase I- Cell separates into two new cells

24. No Interphase II = chromosomes are NOT copied again.
Meiosis II
No Interphase II = chromosomes are NOT copied again.

25. Prophase II ~ TWO cells begin meiosis II

26. Metaphase II chromosomes line up in the middle of the cell

27. Anaphase II -chromosomes are pulled to opposite ends of the cell

28. Telophase II / Cytokinesis ~ The 2 cells divide to form 4 genetically different cells (gametes)

30. End Result of Meiosis Four new cells
Half # chromosomes as parent cell - haploid (n)
Humans – 23 chromosomes

31. MAKING SPERM & EGGS

32. ___________________= MAKING MATURE SPERM
SPERMATOGENESIS
___________________= MAKING MATURE SPERM
Mature & grow flagella

33. CYTOPLASM DIVIDES UNEVENLY; POLAR BODIES DEGENERATE (DIE)
OOGENESIS
__________________ =
MAKING a MATURE EGG
Produces:
1 “good” egg 3
POLAR BODIES
CYTOPLASM DIVIDES UNEVENLY;
POLAR BODIES DEGENERATE (DIE)

34. Sperm donates mostly DNA
WHY MAKE ONLY ONE “GOOD” EGG?
Sperm donates mostly DNA
Most of the cell parts and nutrients needed for baby come from EGG!

35. What are the major differences between Mitosis and Meiosis?

36. Mitosis Meiosis Body cells (Somatic) Sex cells (Gamete)
2 daughter cells same as parent cell (diploid – 2n)
4 daughter cells w/half chrom. (haploid – 1n)
Asexual reproduction
Sexual reproduction