1. MEIOSIS Chapter 12 Honors Genetics
Slide show modified from Kelly Riedell, Tracy Jackson and Kim Foglia

2. BINARY FISSION & MITOSIS
Produces cells that are genetically __________ copies of parent cell
identical

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

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

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

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

7. 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

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

9. MEIOSIS is the way… to make cells with ½ the number of chromosomes
for sexual
reproduction

10. 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

11. 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

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. 2 karyokinesis events occur in meiosis!

16. 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 and SEGREGATION (ANAPHASE I)
4 cells are made and they are haploid
Daughter cells are genetically DIFFERENT

17. 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:

18. WHAT MAKES MEIOSIS DIFFERENT FROM MITOSIS?
1. 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

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

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

21. SEGREGATION separating of doubled chromosomes (homologous pairs) (Anaphase I)

22. SEGREGATION & CROSSING OVER together make even more gamete combinations
See an animation

23. INDEPENDENT ASSORTMENT and SEGREGATION at METAPHASE/ANAPHASE I
Lots of different combinations are possible!
This is why you don’t look exactly like your brothers and sisters even
though you share the same parents!
3rd animation

24. GENETIC RECOMBINATION comes from:
Crossing over
Segregation
Independent assortment
Random fertilization

26. PHASES OF MEIOSIS Meiosis I = MAJOR differences from mitosis
Figure Meiosis
Section 11-4
Meiosis I
= MAJOR differences from mitosis

27. Meiosis II: NOTE- no Interphase II- instead short intermission
(no growth or DNA replication occurs)
Figure Meiosis II
Section 11-4
Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.

28. 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

29. 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
DNA packs into chromosomes
Nuclear membrane/ nucleolus disappear
Spindle fibers appear and attach to chromosomes
Centrosomes migrate to poles
SYNAPSIS and CROSSING OVER OCCURS

30. 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

31. 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)

32. 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

33. MITOSIS vs. MEIOSIS CYTOKINESIS CYTOKINESIS I
2n cell
n cell
DIPLOID
HAPLOID
Cytoplasm splits
into 2 cells using
SAME AS
MITOSIS

34. MITOSIS vs. MEIOSIS INTERPHASE II
2n cell
n 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
SKIP
INTERPHASE II
DNA NOT COPIED

35. 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)

36. 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)

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

38. 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)

39. MITOSIS vs. MEIOSIS CYTOKINESIS CYTOKINESIS II
RESULTS IN FOUR
n cell
RESULTS IN TWO
2n cell
SAME AS MITOSIS
(but cell is now HAPLOID)
Cytoplasm splits

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

41. MAKING SPERM & EGGS

42. 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

43. Starts with a 2n cell called a GERM LINE CELL

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

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

46. 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

47. Stages of Meiosis STEP by STEP animation

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

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

50. Meiosis Animations Frame-by-frame animation