1. Cell Reproduction
Mitosis and Meiosis

2. Cells
Your body is made up of between 10 and 100 trillion cells. (100,000,000,000,000)
One-thousandth of them die every day

3. Cells
Where do all these cells come from?

4. Cellular Reproduction
New cells are made from copies of old cells
This process began occurring before you were born and will continue until after you die

5. Types of Cellular Reproduction
MITOSIS – results in two identical cells; used for the majority of cells in the body
MEIOSIS – results in four cells that are different from the “parents”; used for sex cells only

6. Important Definitions
Chromosome: a single DNA double helix together with proteins that help to organize the DNA
Chromatid: one of the two identical strands of DNA and protein that forms a replicated chromosome
Gene: a unit of heredity; specifies the amino acid sequence of proteins and hence particular traits
Allele: one of several alternative forms of a particular gene
Locus: the physical location of a gene on a chromosome

7. Important Definitions (cont.)
Autosome: chromosome not related to sex
Diploid: referring to a cell with pairs of homologous chromosomes
Haploid: referring to a cell that has only one member of each pair of homologous chromosomes
Homologous Pair: two homologues that are similar in appearance and genetic information that pair during meiosis
Heterozygous: carrying two different alleles of a given gene
Homozygous: carrying two copies of the same allele of a given gene

8. Importance of Chromosomes
All chromosomes come in pairs
Humans have 23 pairs, so a normal cell has 46 chromosomes
All cells need a full set to function properly (except sex cells)

9. Chromosome Number
Before mitosis begins, cells have two of each chromosome (2N)
After chromosomes duplicate, cells have four of each chromosome (4N)
After mitosis, cells have two of each chromosome (2N)

11. Mitosis Mitosis is the division of chromosomes in a cell
It can take a few minutes or a few days
Usually followed by cytokinesis (cell division)
Daughter cells produced after mitosis have the same number of chromosomes as the original cell
Purpose of mitosis is replication of somatic cells and asexual reproduction
Somatic cells include all cells in the body except the egg or sperm

12. Mitosis

15. Chromosome    
Genes    
Total bases    
Sequenced bases[54]     1
3,148
247,200,000
224,999,719 2
902
242,750,000
237,712,649 3
1,436
199,450,000
194,704,827 4
453
191,260,000
187,297,063 5
609
180,840,000
177,702,766 6
1,585
170,900,000
167,273,992 7
1,824
158,820,000
154,952,424 8
781
146,270,000
142,612,826 9
1,229
140,440,000
120,312,298 10
1,312
135,370,000
131,624,737 11
405
134,450,000
131,130,853 12
1,330
132,290,000
130,303,534 13
623
114,130,000
95,559,980 14
886
106,360,000
88,290,585 15
676
100,340,000
81,341,915 16
898
88,820,000
78,884,754 17
1,367
78,650,000
77,800,220 18
365
76,120,000
74,656,155 19
1,553
63,810,000
55,785,651 20
816
62,440,000
59,505,254 21
446
46,940,000
34,171,998 22
595
49,530,000
34,893,953
X (sex chromosome)
1,093
154,910,000
151,058,754
Y (sex chromosome)
125
57,740,000
22,429,293

16. Before Mitosis Begins
Chromosomes are duplicated within the cells (exact copies)
Held together at center
Two strands are called “sister chromatids”

17. Crash Course Biology - Mitosis

18. Stages Of Mitosis
Interphase
Prophase
Metaphase
Anaphase
Telophase

19. Mitosis Step 1: INTERPHASE
During Interphase the cell carries out normal activities such as metabolism and protein synthesis
The DNA in each chromosome is replicated

20. Mitosis Step 2: PROPHASE Sister chromatids thicken
Nuclear membrane breaks down
Two centrioles move apart
Fibers (strands of protein) form between centrioles

22. Mitosis Step 2: METAPHASE Centrioles to opposite ends of cell
Fibers stretch between
Sister chromatids attach to fibers
Sister chromatids line up at center of the cell

24. Mitosis Step 3: ANAPHASE Sister chromatids pulled apart from partner
Fibers pull chromatids towards centrioles at opposite ends of the cell

26. Mitosis STEP 4: TELOPHASE
Each side now has complete set of chromosomes
Fibers disappear
Nuclear membrane re-forms
Cell membrane pinches inwards to form 2 cells

28. Mitosis in Plant Cells 2 Differences No centrioles
Cell wall must re-form between new cells

30. Bazemann Biology – mitosis and meiosis simulation

31. Meiosis

32. Meiosis Process that creates gametes (eggs and sperm)
Cells divide twice

33. Chromosome Number Cells start with two of each chromosome (2N)
Chromosomes double (4N)
Pairs divide (2N)
Sister chromatids divide (N)

34. Importance of Meiosis
During fertilization, sperm (N) and egg (N) fuse to create one cell (2N)
New cell has complete set of chromosomes (half from mother, half from father)

35. Diploid
Di= two sets
Cell that contains both sets of homologus chromosomes
Cell contains
2 complete sets of chromosome
2 complete sets of genes
Number of chromosomes in diploid cell represented by 2N

36. Haploid Means “one set”
Refers to cells that contain only one set of chromosomes
Gametes (sex cells)
Represented by N

37. Meiosis 2 distinct stages Meiosis I Meiosis II
A diploid cell enters here
Meiosis II
At the end of this, the diploid cell that entered meiosis has become 4 haploid cells

40. Meiosis I Before meiosis 1, each chromosome replicates
Then they divide like in mitosis
What happened in mitosis?
PMAT
Tetrad
STRUCTURE MADE WHEN EACH CHROMOSOME PAIRS UP WITH ITS HOMOLOGOUS CHROMOSOME
4 CHROMATIDS IN A TETRAD

41. Independent Assortment
This is the random alignment of the replicated chromosomes
Chromosomes don’t line up in a particular way, this leads to variation.

42. Prophase 1
Each chromosome pairs with its homologous chromosome making a tetrad
As they pair up in tetrads, chromosomes exchange portions of their chromatids in the process …. CROSSING OVER

44. Metaphase1 Anaphase 1 Telophase 1 Spindle fibers attach to chromosomes
The spindles pull homologous chromosomes apart to opposite poles/ends
Telophase 1
Nuclear membranes form and cell separates into two new cells

46. Now what do we have? 2 new daughter cells
Each daughter cell has a set of chromosomes and alleles different from each other and different from the parent diploid cell

47. Meiosis II
Unlike Mitosis, Neither cell goes through a round of chromosome replication
Each cell’s chromosome has 2 chromatids

48. Prophase II
Meiosis resulted in 2 haploid (N) cells, each with ½ the number of chromosomes in the original cell

49. Metaphase 2 Anaphase 2 Telophase 2 Chromosomes line up in middle
Sister chromatids separate and move to opposite poles
Telophase 2
Meiosis II results in 4 haploid (N) daughter cells
4 daughter cells contain haploid number of chromosomes, just 2 each

52. Gamete Formation Male Female
Haploid gametes produced by meiosis are called sperm
Female
Haploid gamete produced by meiosis is called an egg
Cell divisions at the end of meiosis one and two are uneven so one cell gets most of the cytoplasm (the EGG) and the other three are called polar bodies (don’t participate in reproduction)

57. Mitosis vs. Meiosis Mitosis Meiosis
Results in the production of two genetically identical DIPLOID cells
Daughter cells have sets of chromosomes identical to each other and to parent cell
MITOSIS allows body to grow and replace other cells
Asexual reproduction
Meiosis
Results in four genetically different HAPLOID cells
MEIOSIS is how sexually reproducing organisms make gametes