1. MEIOSIS
Slide show modified from Kelly Riedell, Tracy Jackson and Kim Foglia

2. Asexual vs. Sexual Reproduction
In asexual reproduction
One parent produces genetically identical offspring by mitosis
Ex: budding, binary fission, spores
Parent
Bud
0.5 mm

3. ADVANTAGES OF ASEXUAL REPRODUCTION
Can make offspring faster
Don’t need a partner; only 1 “parent” needed

4. DISVANTAGES OF ASEXUAL REPRODUCTION
ALL ALIKE (“clones”)
Species usually CAN’T change and adapt
One disease can wipe out whole population

5. SEXUAL REPRODUCTION
Combines genetic material from 2 parents (sperm & egg)
Offspring are genetically different and unique from parents

6. ADVANTAGES OF SEXUAL REPRODUCTION
Allows for variation in population
Individuals can be different
Provides foundation for EVOLUTION
Allow species adapt to changes in their environment

7. baby would have too many chromosomes!
EGG +
SPERM 
If egg and sperm had same number of
chromosomes as other body cells (2n) . . .
baby would have too many chromosomes!

8. MEIOSIS is the way…
to make cells (gametes) with ½ the number of chromosomes
for sexual
reproduction

9. DIPLOID HOMOLOGOUS CHROMOSOMES All BODY (________ ) cells are diploid
Most cells have 2 copies of each chromosome = ______________
(one from mom; one from dad)
All BODY (________ ) cells are diploid
DIPLOID 2n
HOMOLOGOUS CHROMOSOMES
SOMATIC

10. Chromosomes that determine the sex of an organism = _________________
All other chromosomes that do NOT determine gender = __________
Sex chromosomes
autosomes
Humans have two sex chromosomes (1 pair), which are NOT homologous
and _____ autosomes XX
or XY 44

11. Sex cell has MANY chromosomes including 1 sex chromosome
Sex chromosomes vs. Sex cell…NOT the same!!!
X or Y= sex chromosome
Sex cell has MANY chromosomes including 1 sex chromosome

12. HAPLOID
Some cells have only one copy of each chromosome = _____________
All sperm and egg cells
are haploid
HAPLOID 1n

13. Review…MITOSIS
Makes ___ cells genetically _________ to parent cell & to each other
Makes ___ cells
Makes __________
Used by organisms to: increase size of organism, repair injuries, replace worn out cells 2
identical 2n
SOMATIC (body)

14. MEIOSIS 4 1n Gametes (sperm & eggs)
Makes ____ cells genetically different from parent cell & from each other
Makes _____ cells
Makes ______________
Used for ____________ 1n
Gametes
(sperm & eggs)
Sexual reproduction

15. WHAT MAKES MEIOSIS DIFFERENT FROM MITOSIS ?
2 divisions instead of 1
Meiosis I and Meiosis II (PMATc I & PMATc II)
SYNAPSIS & CROSSING OVER (PROPHASE I)
INDEPENDENT ASSORTMENT (METAPHASE I) and SEGREGATION (ANAPHASE I)
4 cells are made and they are haploid
Daughter cells are genetically DIFFERENT

16. WHAT MAKES MEIOSIS DIFFERENT FROM MITOSIS?
Homologous chromosomes pair up during ________________
= ______________
PROPHASE I
called SYNAPSIS
This group of FOUR (4)
chromatids is called a
_________________
TETRAD
Images modified from:

17. WHAT MAKES MEIOSIS DIFFERENT FROM MITOSIS?
Exchange of DNA between homologous pairs = _____________ during PROPHASE I
CROSSING OVER
Allows shuffling of genetic material called genetic recombination
Place(s) where crossing over
happens
= ____________________
CHIASMATA

18. Allows for_________________ in different combinations
CROSSING OVER
rearranging of DNA
Allows for_________________
in different combinations
After crossing over, chromatid arms are________________ anymore
NOT IDENTICAL

19. STARTS WITH A DIPLOID (2n) CELL CALLED A “GERM LINE CELL”
**only 2n cell that undergoes meiosis
2 karyokinesis events occur in meiosis!

20. INDEPENDENT ASSORTMENT the random alignment of homolgous chromosomes at metaphase plate (Metaphase I)

21. SEGREGATION separating of doubled chromosomes (Anaphase I)

22. GENETIC RECOMBINATION comes from:
Before gametes meet…
Crossing over
Segregation
Independent assortment
After gametes meet…
Random fertilization

23. MITOSIS vs. MEIOSIS INTERPHASE INTERPHASE I
2n cell
2n cell
DNA is spread out as chromatin
Nuclear membrane/nucleolus visible
DNA is copied during S phase
Makes stuff new cell needs in G2
Cell Grows
SAME AS
MITOSIS

24. MITOSIS vs. MEIOSIS PROPHASE PROPHASE I
2n cell
2n cell
DNA packs into chromosomes
Nuclear membrane/ nucleolus disappear
Spindle fibers appear and attach to chromosomes
Centrosomes migrate to poles
Same as mitosis EXCEPT:
SYNAPSIS OCCURS  TETRADS FORM and CROSSING OVER OCCURS

25. MITOSIS vs. MEIOSIS METAPHASE METAPHASE I
2n cell
2n cell
Chromosomes line up in middle in single file line
Chromosomes line up in middle with
homologous partner
Independent assortment occurs

26. MITOSIS vs. MEIOSIS ANAPHASE ANAPHASE I
2n cell
2n cell
Polar fibers lengthen cell
Chromatids split
Polar fibers lengthen cell
Chromatids stay together Homologous pairs split (SEGREATION OCCURS)

27. MITOSIS vs. MEIOSIS TELOPHASE TELOPHASE I
2n cell
n cell
See TWO nuclei
Nuclear membrane/ nucleolus return
DNA spreads out as chromatin
Spindle fibers disappear
SAME AS
MITOSIS
(except haploid # of chromosomes not diploid #)

28. MITOSIS vs. MEIOSIS CYTOKINESIS CYTOKINESIS I
2n cell
n cell
DIPLOID
HAPLOID
Cytoplasm splits
into 2 cells using
SAME AS
MITOSIS
(except haploid # of chromosomes not diploid #)

29. MITOSIS vs. MEIOSIS INTERPHASE II
2n cell
n cell
SKIP
INTERPHASE II  RESTING PHASE INSTEAD
DNA NOT COPIED BUT CENTROSOMES/CENTRIOLES ARE COPIED
DNA is spread out as chromatin
Nuclear membrane/nucleolus visible
DNA is copied during S phase
Makes stuff new cell needs in G2
Cell Grows

30. MITOSIS vs. MEIOSIS PROPHASE PROPHASE II
n cell
2n cell
DNA packs into chromosomes
Nuclear membrane/ nucleolus disappear
Spindle fibers appear and attach to chromosomes
Centrosomes migrate to poles
SAME AS MITOSIS
(but cell is now HAPLOID)

31. MITOSIS vs. MEIOSIS METAPHASE METAPHASE II
n cell
2n cell
Chromosomes line up in middle in a single file line
SAME AS MITOSIS
(but cell is now HAPLOID)

32. MITOSIS vs. MEIOSIS ANAPHASE ANAPHASE II
2n cell
n cell
Chromatids split and move apart
SAME AS MITOSIS
(but cell is now HAPLOID)

33. MITOSIS vs. MEIOSIS TELOPHASE TELOPHASE II
2n cell
n cell
See TWO nuclei
Nuclear membrane/ nucleolus return
DNA spreads out as chromatin
Spindle fibers disappear
SAME AS MITOSIS
(but cell is now HAPLOID)

34. MITOSIS vs. MEIOSIS CYTOKINESIS CYTOKINESIS II
RESULTS IN FOUR
n cell
RESULTS IN TWO
2n cell
Four cells are made NOT two cells
Cells are haploid NOT diploid
DNA is different in all cells
Cytoplasm splits

35. Ways Meiosis is different?
Meiosis I is VERY different
P1: Synapsis  Tetrad formation  Crossing over
M1: Independent Assortment
A1: Segregation
T/C1: 2 cells are made (LIKE MITOSIS) but HAPLOID (not diploid) cells are made
Meiosis II is EXACTLY the SAME as mitosis EXCEPT…
Occurs in HAPLOID cells throughout the process
4 cells are made (genetically DIFFERENT

36. Ways Meiosis is different?
2nd and 4th animations

37. MAKING SPERM & EGGS

38. 2 TYPES: Gametogenesis =
process of forming gametes (n) from diploid (2n) cells
2 TYPES:
Spermatogenesis = process of forming sperm cells
After division all 4 cells undergo differentiation to become sperm cells
The cells elongate and grow tail (a flagella)
Oogenesis = process of forming ovum (egg) cell and 3 polar bodies

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

40. Sperm provides DNA to the zygote.
All the starting nutrients, organelles, molecule building blocks, etc. have to come from the ovum (egg)

41. OOGENESIS __________________ = MAKING a MATURE EGG Produces:
1 “good” ovum (egg) 3
POLAR BODIES
CYTOPLASM DIVIDES UNEVENLY
Polar bodies are smaller and are later destroyed using APOPTOSIS

42. Putting it all together…
meiosis  fertilization  mitosis + development 46 46 23 46 46 46 46 46 23 46 46
egg 46 46
sperm

43. Abnormal Chromosome Number
When nondisjunction occurs
Pairs of homologous chromosomes do NOT separate normally during meiosis
Anaphase I or Anaphase II
Gametes contain 2 copies or NO copies of a particular chromosome

44. What happens when meiosis goes wrong?  NONDISJUNCTION!!!

45. Nondisjunction of sister chromatids in meiosis II
Figure 15.12a, b
Meiosis I
Nondisjunction
Meiosis II
Gametes
n + 1
n  1
n – 1
n –1 n
Number of chromosomes
Nondisjunction of homologous
chromosomes in meiosis I
Nondisjunction of sister
chromatids in meiosis II
(a)
(b)