1. MEIOSIS Lecture #21 Honors Biology
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 cell division
Ex: binary fission

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. + 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 with ½ the number of chromosomes; Needed
for sexual
reproduction

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. HOW IS MEIOSIS SIMILAR TO MITOSIS ?
Contains PMATc
Prophase, Metaphase, Anaphase & Telophase/Cytokinesis
ALL events in these phases are EXACTLY the same as mitosis
Uses mitotic spindle to move chromosomes
Daughter cells are made

16. HOW IS 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)
Segregation (ANAPHASE I)
4 cells are made and they are haploid
Daughter cells are genetically DIFFERENT
Different functions:
Mitosis  growth, maintenance & repair
Meiosis  sexual reproduction

17. 2 karyokinesis (nucleus division) events occur in meiosis!
DIFFERENCE #1:
2 divisions
2 karyokinesis (nucleus division) events occur in meiosis!
PMATc I
PMATc II

18. DIFFERENCE #2: Synapsis
Homologous chromosomes pair up during ________________
= ______________
PROPHASE I
called SYNAPSIS
This group of FOUR (4)
chromatids is called a
_________________
TETRAD
Images modified from:

19. DIFFERENCE #2: Crossing Over
Exchange of DNA between homologous pairs = _______________ during PROPHASE I
CROSSING OVER
**called genetic recombination
Place(s) where crossing over
happens
= ____________________
CHIASMATA

20. DIFFERENCE #3: Independent Assortment homolgous chromosome pairs line up NEXT TO their partner at metaphase plate (Metaphase I)

21. DIFFERENCE #4: Segregation Homologous chromosome pairs separate of (chromatids do NOT separate yet…) (Anaphase I)

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

23. Meiosis II: NOTE- no Interphase II- instead short intermission
(no growth or DNA replication occurs)
Figure Meiosis II
Section 11-4
Same as mitosis but with HAPLOID cells
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.

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

25. MAKING SPERM & EGGS

26. 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

27. Starts with a 2n cell called a GERM LINE CELL
(ovary or testes)

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

29. 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

30. Stages of Meiosis STEP by STEP animation

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

32. 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

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

34. Yay…The End

35. Meiosis Square Dance