1. Reproduction
Sexual and Asexual
Mitosis and Meiosis

2. Asexual Sexual Fission (protists) Budding (yeast…a fungus)
The fusion (combining) of two gametes (sex cells…like sperm and egg) to create a whole new being.
Fission (protists)
Budding (yeast…a fungus)
Mitosis (humans!)
Sperm
Each has only ½ the genetic information needed
Egg
Tonya Scott shared this powerpoint and I think it has fantastic ideas/great vocabulary. I added in my own stuff (really my variation of the sciencespot.net) to go along with the worksheet notes/cloze notes that I feel the kids will understand. Be careful. The MEIOSIS notes are very similar to the MITOSIS notes (in fact, I will be printing them on a different color paper). Since we don’t have time to do but so much, I will likely do the notes in class together and then have the kids cut them into strips and staple them into a slight variation of the “flip book” idea from sciencespot.net. Please note that the templates for the flip books are available in our GoogleDocs, but also at sciencespot.net.
1 original cell copies = 2 whole new cells
½ + ½ = 1 whole new cell
Used to create a whole new being…with a new combination of genetic information.
Used to create a whole new being…with the same combination of genetic information. 2

3. Binary fission…in amoeba

4. Budding…in yeast

5. Mitosis
Happens on “my-toes-es, my-nose-es, my ear-lobes-es…ALL OVER THE BODY”
How a cell with 100% genetic info makes a copy. No partner needed.
One cell of 100% to TWO cells that each have 100%
Growth, repair, replacement.
Asexual reproduction.
IPMATC

6. Three reasons why cells reproduce by asexual reproduction:. 1. Growth
Three reasons why cells reproduce by asexual reproduction: Growth Repair Replacement
Skin cancer - the abnormal growth of skin cells - most often develops on skin exposed to the sun.
Cell that reproduce by asexual reproduction reproduce constantly.

7. Cell division Vocabulary
Sexual (reproduction)
Asexual (reproduction)
Budding
Fission
Mitosis
Meiosis
Gametes

8. Meiosis

9. Meiosis – A Source of Distinction
Why do you share some but not all characters of each parent?
What are the rules of this sharing game?
At one level, the answers lie in meiosis.

10. Meiosis does two things -
1) Meiosis takes a cell with two copies of every chromosome (diploid) and makes cells with a single copy of every chromosome (haploid).
This is a good idea if you’re going to combine two cells to make a new organism. This trick is accomplished by halving chromosome number.
In meiosis, one diploid cells produces four haploid cells.

11. 2) Meiosis scrambles the specific forms of each gene that each sex cell (egg or sperm) receives.
This makes for a lot of genetic diversity. This trick is accomplished through independent assortment and crossing-over.
Genetic diversity is important for the evolution of populations and species.

12. Why do we need meiosis?
Meiosis is necessary to create ½ (half) the number of chromosomes going into the sex cells
100%....down to gametes of 50% each
Why use only ½ the chromosomes for gametes?
At fertilization the male and female sex cells will provide ½ of the chromosomes each – so the offspring has genes from both parents
50% + 50% = 100%...so gametes start at 50%

13. Prophase I
During the time before Prophase I, the diploid (2n) cell has already doubled its DNA to become tetraploid (4n).
The cell prepares for division by coiling its DNA into chromosomes, pairing homologous chromosomes (matched pairs) to form tetrads, and dissolving the nuclear membrane during Prophase I.
Parts of chromosomes may be exchanged through crossing over.

14. Metaphase I Before After The formation of the spindle.
It also shows how the tetrads align at the equator of the cell.
Each pair of homologous (matching) chromosomes attaches to the spindle.
Before
After

15. Anaphase I
Homologous chromosomes separate during Anaphase I, but the sister chromatids stay together as they move toward opposite ends of the cell.

16. Telophase I and Cytokinesis I
During Telophase I, the chromosomes gather at the poles and uncoil to become the thin, threadlike form called chromatin.
The nuclear membrane also reforms.
The physical division of the parent cell in Cytokinesis I occurs differently for animals and plants. In animal cells, a cleavage furrow pinches inward near the equator of the cell to form two daughter cells. In plants, a cell plate forms near the center of the cell and spreads outward to separate the two daughter cells.
The diploid (2n) daughter cells then begin Prophase II of the second division.

17. Telophase I and Cytokinesis I

18. Prophase II
During Prophase II, the chromosomes coil and the nuclear membrane disappears as each daughter cell prepares for division.

19. Metaphase II
The spindle forms and the pairs of sister chromatids align at the equator of the cell.

20. Anaphase II
“Sister” chromatids separate during Anaphase II.

21. Telophase II (Cytokinesis II)
The chromatids reach the poles and uncoil into the thin, threadlike chromatin in Telophase II. The nuclear membrane also reforms.
Cytokinesis II

22. Cytokinesis II (and Telophase II)
In Cytokinesis II each of the two diploid (2n) daughter cells formed in the first division are physically divided into two haploid (n) daughter cells.

23. Meiosis Parent cell – chromosome pair Chromosomes copied
1st division - pairs split
2nd division – produces 4 gamete cells with ½ the original no. of chromosomes

24. The Stages of Meiosis:
aka: Reduction Division

25. Meiosis I : Separates Homologous Chromosomes
Interphase
Each of the chromosomes replicate
The result is two genetically identical sister chromatids which remain attached at their centromeres

26. Prophase I This is a crucial phase for mitosis.
During this phase each pair of chromatids don’t move to the equator alone, they match up with their homologous pair and fasten together (synapsis) in a group of four called a tetrad.
Extremely IMPORTANT!!! It is during this phase that crossing over can occur.
Crossing Over is the exchange of segments during synapsis.

27. Metaphase I
The chromosomes line up at the equator attached by their centromeres to spindle fibers from centrioles.
Still in homologous pairs

28. Anaphase I
The spindle guides the movement of the chromosomes toward the poles
Sister chromatids remain attached
Move as a unit towards the same pole
The homologous chromosome moves toward the opposite pole
Contrasts mitosis – chromosomes appear as individuals instead of pairs (meiosis)

29. Telophase I This is the end of the first meiotic cell division.
The cytoplasm divides, forming two new daughter cells.
Each of the newly formed cells has half the number of the parent cell’s chromosomes, but each chromosome is already replicated ready for the second meiotic cell division

30. Cytokinesis Occurs simultaneously with telophase I
Forms 2 daughter cells
Plant cells – cell plate
Animal cells – cleavage furrows
NO FURTHER REPLICATION OF GENETIC MATERIAL PRIOR TO THE SECOND DIVISION OF MEIOSIS

31. Figure 13.7 The stages of meiotic cell division: Meiosis I

32. Meiosis II : Separates sister chromatids
Proceeds similar to mitosis
THERE IS NO INTERPHASE II !

33. Prophase II
Each of the daughter cells forms a spindle, and the double stranded chromosomes move toward the equator

34. Metaphase II
The chromosomes are positioned on the metaphase plate in a mitosis-like fashion

35. Anaphase II The centromeres of sister chromatids finally separate
The sister chromatids of each pair move toward opposite poles
Now individual chromosomes

36. Telophase II and Cytokinesis
Nuclei form at opposite poles of the cell and cytokinesis occurs
After completion of cytokinesis there are four daughter cells
All are haploid (n)

37. Figure 13.7 The stages of meiotic cell division: Meiosis II

38. One Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment
Independent assortment produces 2n distinct gametes, where n = the number of unique chromosomes.
In humans, n = 23 and 223 = 6,000,0000.
That’s a lot of diversity by this mechanism alone.

40. Another Way Meiosis Makes Lots of Different Sex Cells – Crossing-Over
Crossing-over multiplies the already huge number of different gamete types produced by independent assortment.

41. Mitosis vs. Meiosis

42. The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis
Mitosis
The first (and distinguishing) division of meiosis

43. Mitosis vs. Meiosis

44. Boy or Girl? The Y Chromosome “Decides”
X chromosome
Y chromosome

45. Boy or Girl? The Y Chromosome “Decides”

46. Meiosis – division error
Chromosome pair

47. Meiosis error - fertilization
Should the gamete with the chromosome pair be fertilized then the offspring will not be ‘normal’.
In humans this often occurs with the 21st pair – producing a child with Downs Syndrome

48. 21 trisomy – Downs Syndrome
Can you see the extra 21st chromosome?
Is this person male or female?