1. Mitosis and Meiosis aka Cell Division
Cell Reproduction
Mitosis and Meiosis
aka Cell Division

2. Mitosis
New cells are produced by the process of cell division, the dividing of a cell into new cells. Also, in cell division, both nucleus and cytoplasm divide.

3. Mitosis Vocabulary What is a homologous chromosome?
Refers to pairs of like chromosomes
What is diploid?
The total number of chromosomes
What is haploid?
Half the total of diploid chromosomes

4. Mitosis Vocabulary… What does “2n” represent?
This is the symbol for the diploid number.
“n” is equal to the number of pairs of chromosomes
How many chromosomes in humans?
46 – this is the “2n” number.
“n” = ?

5. Mitosis Vocabulary… What is a parent cell?
Refers to the cell that will go through cell division
What are daughter cells?
Cells that are formed in cell division – the result of cell reproduction

6. Chromosomes What are chromosomes?
Carrier of genetic materials, thread-like fibers found in the nucleus
What happens to the chromosomes during cell division?
During cell division, the chromosomes are passed to the new cells that are formed
They are composed of genes

7. Chromosomes… What are sister chromatids?
two distinct strands that make up chromosomes
What is a centromere?
Structure that holds the chromatids together

8. Chromosomes… What are genes?
Made up of DNA and are units of heredity; unique to everyone
What are traits?
Are physical and unseen characteristics.
Examples:
physical: color of skin or eyes
unseen: blood type or intelligence level

9. Chromosomes… What are living things made of?
Made of cells that contain a certain number of chromosomes.
Examples: body cells of an onion plant contains 16 chromosomes
How many chromosomes does a human have?
46 chromosomes

10. What is mitosis?
Type of cell division by which chromosomes double to form two complete identical cells or daughter cells
Each daughter cell receives the same number of chromosomes that the parent cell had

11. Why do cells divide?
Cell size is an important factor in causing a cell to divide
A cell will not continue to grow indefinitely, when a cell reaches a certain size, it will divide

12. The Cell Cycle
Consists of 3 stages:
Interphase
Mitosis
Cytokinesis

14. What is interphase? First stage of the cell cycle
“resting” stage is the period in which cells carry out many activities other than mitosis
Interphase is not a part or period of mitosis; this phase precedes mitosis and follows cytokinesis

15. Stages of interphase
G1 Phase – the cell doubles in size, enzymes and organelles, such as mitochondria and ribosomes, roughly double in number
S Phase – the DNA that makes up the chromatin replicates – chromosomes double. Example: human chromosomes go from 46 chromosomes to 92 chromosomes
G2 Phase – the cell undergoes rapid growth that prepares it for mitosis, makes the necessary enzymes and structures

17. Second stage of the cell cycle
Stages of mitosis
Prophase
Metaphase
Anaphase
Telophase
Second stage of the cell cycle

18. What happens during prophase?
Chromosomes come in pairs, appear shorter and thickened
Nuclear membrane and nucleolus disintegrate or disappear
Centrioles move to the opposite ends of the cell
Spindle fibers form at the centrioles

20. What happens during metaphase?
Paired thick chromatids move to the center or equator of the cell and line up along the equator
The centromere of each pair of chromatid is attached to a spindle fiber from the centriole

22. What happens during anaphase?
Centromeres split and the spindle fibers pull the sister chromatids apart
The paired chromatids are now individual chromosomes
Separated chromosomes are moved towards the opposite poles of the cells or to the ends of the spindle fibers

24. What happens during telophase?
In animal cells, cytoplasm pinches together along the equator until two daughter cells are formed
In plant cells, a cell plate forms between the 2 new cells
Chromosomes become thread-like by uncoiling
Nuclear membrane and nucleolus reform
Spindle fibers begin to breakdown

26. What is cytokinesis? Third stage of the cell cycle
The division of the cytoplasm
Produces 2 new daughter cells

27. Animal or plant division
Animal cells:
The cell pinches in on both sides to form a cleavage furrow.
Plant cell:
The cell forms a cell plate between to 2 new cells.

28. What does mitosis accomplish?
Reproduction of cells
Equal distribution of DNA (genetic information) to each daughter cell

30. Example of mitosis Fruit Fly has 8 diploid chromosomes
Mitosis = parent cell division into 2 daughter cells
Fruit fly – how many chromosomes at each phase?
Interphase – (still one cell)
Prophase - (still one cell)
Metaphase - (still one cell)
Anaphase - (still one cell)
Telophase – (two new cells)

31. Normal cells Animal Cells/Diploid Humans – 46 Cat – 38 Cow – 60
Dog – 78
Fruit Fly – 8
Goldfish – 94
Grasshopper – 14
Housefly - 12
Plant cells/Diploid
Onion – 16
Pea – 14
Apple – 34
Sunflower – 34
Plum – 48
Rice – 12
Tobacco – 48

32. Normal cells…
Notice that the numbers for all organisms listed are even numbers. Chromosomes in the body cells of all organisms occur in pairs.
Homologous chromosomes – refers to pairs of like chromosomes
Example: In cat cells there are 19 pairs of chromosomes

33. What is cancer? Uncontrolled cell division
The cell never goes into interphase
Always in a state of division

34. What factors contribute to the development of cancer?
Genetic malfunction where enzymes that start and stop the cell cycle are either not produced or are over produced
When cells no longer respond to the chemicals that are secreted to prevent the overcrowding of cells. This is known as contact inhibition
Environmental factors: cigarette smoke, air and water pollution, and exposure to ultraviolet radiation

35. What are the steps of cancer?
Genes controlling enzyme production are disrupted
Changes occur in the cell cycle for cell reproduction
Environmental factors trigger the cancer cell to grow
Cancer cells crowd normal cells preventing nutrients form getting to the normal cells
A tumor forms
Cancer cells break away from original cancer growth
Cancer cells enter circulatory system and spread throughout the body
New tumors form disrupting normal organ function

36. Practice quiz What is the diploid number for human chromosomes? 46
What holds sister chromatids together?
Centromere
What are the stages of the cell cycle?
Interphase, mitosis, cytokinesis

37. Practice quiz… What are the stages of mitosis? (in order)
Prophase, metaphase, anaphase, telophase
In what phase does the DNA double?
Interphase
In what phase do the chromosomes line up in the center of the cell?
metaphase

38. Meiosis
Cell division where one diploid cell (2n) produces four haploid (n) cells called sex cells or gametes
These cells have half the number of chromosomes as a body cell of a parent

39. Meiosis vocabulary What is a gamete?
Male and female sex cells; the sperm and egg
What is the male gamete?
Sperm; has 23 chromosomes
What is the female gamete?
Egg; has 23 chromosomes

40. Meiosis vocabulary… What is a zygote?
A fertilized egg – has a diploid number (2n) of chromosomes
What is sexual reproduction?
The pattern of reproduction that involves the production and fusion of haploid sex cells
What is a diploid cell?
Cell containing two of each kind of chromosome from the parent

41. Meiosis vocabulary… What is a haploid cell?
Cell containing one of each kind of chromosome from the parent
What is an allele?
Gene form for each variation of a trait of an organism. Example: gene for height can express tall or short
Homologous chromosomes:
Pairs of like chromosomes even though the alleles may be different – so they are not identical chromosomes – sibling variation

42. The Phases of Meiosis Meiosis I Interphase Prophase I Metaphase I
Anaphase I
Telophase I
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II

43. Interphase Carries out metabolic activities of the cell
Replicates its chromosomes
Precedes meiosis 1

44. Prophase I Chromosomes coil up and spindle form
Homologous chromosomes pair up and a four-part structure called a tetrad forms

45. During prophase I…
Tightly wound tetrads get so close to one another that the genetic material from one homologous pair exchanges with the other creating new combinations of alleles in the genetic code
Nuclear membrane disappears
Nucleolus disappears

46. What is crossing over?
Exchange of genetic material by non-sister chromatids during prophase I
Results in new combinations of alleles

47. Metaphase I Tetrads line up at the equator
Homologous chromosomes are lined up in pairs along the midline or equator of the cell
Spindle fibers attach to the centromere on each pair
The pairs are not attached to each other

49. Anaphase I
Homologous chromosomes are separated and pulled to opposite poles of the cell
The centromeres do not split during this phase
Each new cell receives only one chromosome from each homologous pair

51. Telophase I Spindle breaks down Chromosomes uncoil
Cytoplasm divided in 2
Each cell has half the genetic information from the original cell
Chromosomes are still doubled containing two sister chromatid
Nuclear membrane reforms
Two diploid daughter cells formed

53. Meiosis II Is there an interphase in Meiosis II?
No. Chromosomes do not replicate
The cells go directly from meiosis I to meiosis II

54. Prophase II Spindle forms in each of the two new cells
Chromosomes are still coiled as sister chromatids
Nuclear membrane disappears
Nucleolus disappears

55. Metaphase II Chromosomes line up at the equator of the cell
Spindle fibers attach to the centromeres

56. Anaphase II Centromeres split
Spindle fibers pull separated chromatids to opposite poles of the cell

57. Telophase II Spindle fibers disappear Chromosomes uncoil
Nuclear membrane reforms
Nucleolus reforms
Cytoplasm divides
Each cell now has half the chromosomes that its parents had
Four daughter haploid cells are formed

59. What are the two divisions of meiosis?
Meiosis I and Meiosis II
Meiosis I
When homologous chromosomes come together and separate
Meiosis II
The division that results in 4 daughter cells, each with half the chromosomes present in the original cell

60. What is genetic recombination?
Genetic variation due to crossing over and random assortment
How many ways can the chromosomes line up? 2

61. How do you find the total number of different kinds of sperm and egg that can be produced?
Take the number of pairs and place it as the exponent with a base of 2
Example: in humans there are 23 pairs of chromosomes
For sperm: 223 = over 8 billion
For egg: 223 = over 8 billion

62. What is the total when fertilization occurs?
223 * 223 = 70 trillion zygotes are possible

63. What is oogenesis?
Refers to the formation of the egg cell

64. What is spermatogenesis?
Refers to the formation of the sperm cell