1. Gametes and Meiosis
Making gametes…

2. Interest Grabber
1. How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis?
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?
3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have?
46 chromosomes
= 92; a developing embryo would not survive if it contained 92 chromosomes.
Sperm and egg should each have 23 chromosomes.

3. + EGG SPERM  If egg and sperm had same number of
Image by Riedell
Image by Riedell
EGG +
SPERM 
If egg and sperm had same number of
chromosomes as other body cells . . .
baby would have too many chromosomes!

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

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

6. HOMOLOGOUS CHROMOSOMES
SAME SIZE
SAME SHAPE
CARRY GENES for the SAME TRAITS
BUT ______________!
(Don’t have to have the SAME CHOICES)
Image modified by Riedell
NOT IDENTICAL

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

8. 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)

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

10. MEIOSIS I

11. CROSSING OVER PROPHASE I SYNAPSIS
Homologous chromosomes pair up during ________________
= ______________
PROPHASE I
SYNAPSIS
This group of FOUR (4)
chromatids is called a
_________________
TETRAD
Images modified from:

12. CROSSING OVER
1. Exchange of DNA between homologous pairs = _____________ during PROPHASE I
CROSSING OVER
Allows shuffling of genetic material

13. Allows for_________________ in different combinations
Image modified by Riedell
CROSSING OVER
rearranging of DNA
Allows for_________________
in different combinations
After crossing over, chromatid arms are________________ anymore
NOT IDENTICAL

15. MEIOSIS II

16. WHAT MAKES MEIOSIS DIFFERENT ?
SYNAPSIS & CROSSING OVER (PROPHASE I)
SEGREGATION &
INDEPENDENT ASSORTMENT (ANAPHASE I)
3. Skip INTERPHASE II (NO S)
CELL DIVIDES TWICE, BUT…
ONLY COPIES DNA ONCE

17. WHAT MAKES MEIOSIS DIFFERENT ?
2.Separation during ANAPHASE I
SEGREGATION &
INDEPENDENT ASSORTMENT
Separates gene choices and allows shuffling of genetic material

18. SEGREGATION (Anaphase I)

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

20. INDEPENDENT ASSORTMENT

21. INDEPENDENT ASSORTMENT at 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!

22. WHAT MAKES MEIOSIS DIFFERENT ?
Crossing over Segregation Independent assortment
are ALL ways MEIOSIS results in =______________________________
So daughter cells are ______________
from parents and from each other
GENETIC RECOMBINATION
different

23. WHAT MAKES MEIOSIS DIFFERENT ?
3. Skip INTERPHASE II (No S)
CELL DIVIDES TWICE, BUT …
ONLY COPIES ITS DNA ONCE
MITOSIS: G1 S G2 P M A T C       
MEIOSIS:
( I ) G1 A T C S G2 P M        P M A T C
( II )    

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

25. MITOSIS vs MEIOSIS PROPHASE PROPHASE I
DNA scrunches into chromosomes Nuclear membrane/ nucleolus disappear Centrioles/spindle fibers appear
DNA scrunches into chromosomes
Nuclear membrane/
nucleolus disappear
Centrioles/ spindle fibers appear
Homologous pairs match up

26. MITOSIS vs MEIOSIS METAPHASE METAPHASE I
Chromosomes line up in middle
Chromosomes line up in middle
with homologous partner

27. MITOSIS vs MEIOSIS ANAPHASE ANAPHASE I
APART:
APART:
Chromatids split
Chromatids stay together Homologous pairs split

28. MITOSIS vs MEIOSIS TELOPHASE TELOPHASE I
See TWO nuclei
Nuclear membrane/
nucleolus return
DNA spreads out as chromatin
Spindle/centrioles disappear
SAME AS MITOSIS

29. MITOSIS vs MEIOSIS CYTOKINESIS CYTOKINESIS I
Cytoplasm splits
into 2 cells
SAME AS
MITOSIS

30. MITOSIS vs MEIOSIS INTERPHASE II
DNA is spread out as chromatin
Nuclear membrane/ nucleolus visible
DNA is copied during S phase
SKIP
INTERPHASE II
DNA NOT COPIED

31. MITOSIS vs MEIOSIS PROPHASE PROPHASE II
DNA scrunches into chromosomes
Nuclear membrane/ nucleolus disappear
Centrioles/ spindle fibers appear
SAME AS MITOSIS

32. MITOSIS vs MEIOSIS METAPHASE METAPHASE II
Chromosomes line up in middle
SAME AS MITOSIS

33. MITOSIS vs MEIOSIS ANAPHASE ANAPHASE II
Chromatids split and move apart
SAME AS MITOSIS

34. MITOSIS vs MEIOSIS TELOPHASE TELOPHASE II
Two nuclei
Nuclear membrane/ nucleolus returns
Centrioles/spindle fibers disappear
DNA spreads out as
chromatin
SAME AS MITOSIS

35. MITOSIS vs MEIOSIS CYTOKINESIS CYTOKINESIS II
SAME AS MITOSIS
Cytoplasm splits

36. MAKING SPERM & EGGS

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

38. Sperm provides DNA
All the starting nutrients,
organelles, molecule building blocks,
etc. have to come from the egg.

39. CYTOPLASM DIVIDES UNEVENLY
OOGENESIS
__________________ =
MAKING a MATURE EGG
Produces:
1 “good” egg 3
POLAR BODIES
CYTOPLASM DIVIDES UNEVENLY

40. 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!

41. APOPTOSIS LYSOSOMES POLAR BODIES DEGENERATE (DIE) “Self digest” Using
________________
LYSOSOMES
APOPTOSIS
= __________________
“cell suicide” for good of organism