1. Honors Biology Chapter 9
JUST THE FACTS!

2. Cell Reproduction = the process by which cells divide to create new cells = cell division

3. Why Most Cells Divide: 1. Surface Area to Volume Ratio:
As cells grow their volume increases faster than their surface area.
This decreases the surface area to volume ratio.
So, diffusion and other forms of transport cannot happen fast enough to keep the cell alive.

4. What would the volume of a cell be if each side measured 4 cm?

5. Why Most Cells Divide: (cont.)
2. DNA Overload:
Genetic information cannot be processed fast enough in a really large cell to keep the cell functioning.
Giant amebas have 2 nuclei with 2 sets of chromosomes to overcome this problem!

6. Cell Cycle = the orderly sequence of growth and division for a cell
Events of the Cell Cycle:
G1 Phase: Period of growth before DNA is duplicated
S Phase: DNA is replicated (duplicated)

7. Cell Cycle Events of the Cell Cycle: (Cont.)
G2 Phase: More growth, and organelles and materials needed for cell division are made.
M Phase: Cell division
2 Parts:
Nuclear Division (Mitosis)
Cytoplasm Division (Cytokinesis)

8. Cell Cycle

10. B. The Cell Cycle- Series of events that cells go through as they grow and divide
1. Consists of 4 phases (interphase= G1, S, and G2)
a. M phase (mitosis)- division of cell nucleus and cytokinesis
b. G1 phase (gap)-periods of growth and activity
c. S phase (synthesis)- DNA synthesized (duplicated)
d. G2 phase (gap)- period of growth and acitivity. Organelles produced.

11. Two Types of Nuclear Division
WHO?
(Type of Cell)
WHY?
(Purpose)
Mitosis
Somatic (Body) Cells = any cell but a sex cell
Make identical copies of the original cell for growth, repair and maintenance = clones.
Meiosis
Sexual reproductive cells (sex cells)
To reduce the chromosome number by half.
To increase genetic variation

12. D. Cytokinesis- division of cytoplasm and organelles
D. Cytokinesis- division of cytoplasm and organelles. Follows mitosis or meiosis (division of the nucleus)
1. Animal cells- cell membrane drawn inward until cytoplasm is pinched into two nearly equal parts
2. Plant cells- cell plate forms midway between divided nuclei. Gradually develops into separating membrane. Eventually cell wall begins to appear.

13. Asexual Reproduction Single parent produces offspring
All offspring are genetically identical to one another and to parent

14. Chromosome = thin thread of DNA wrapped around histone proteins.
Structure:

15. Chromosome

16. A. Chromosomes- genetic information carried on chromosomes
1. Before cell division each chromosome is replicated (copied)
2. Each chromosome consists of two identical “sister” chromatids
3. Each pair of chromosomes attached to area called centromere

17. Chromosome Number Chromosome number is expressed as either:
1. Diploid = 2n = the number of chromosomes found in somatic cells, where n = the number of homologous pairs.

18. Chromosome Number (cont.)
Haploid Number = n = the number of chromosomes in a gamete of that organism. (Half the diploid number)
Examples:
Humans: n = 23
Gorillas: n = 24
Pea Plants: n = 7
Why is it necessary for gametes to have half the chromosome number of somatic cells?

19. CHROMOSOMES
Homologous chromosomes = a matched set; each chromosome has a partner chromosome that looks just like it and contains genes for the same things.

20. Homologous Chromosomes Carry Different Alleles
Cell has two of each chromosome
One chromosome in each pair from mother, other from father
Paternal and maternal chromosomes carry different alleles (allele = different form of a gene, but for the same inherited trait. Ex. We have genes for eye color, but you could have an allele for brown eyes, or an allele for blue eyes.

21. Mitosis Details: Interphase
Usually longest part of the cycle
Cell increases in mass
Number of cytoplasmic components doubles
DNA is duplicated

22. Mitosis Details: Prophase
Duplicated chromosomes begin to condense

23. Mitosis Details: Late Prophase
New microtubules are assembled
One centriole pair is moved toward opposite pole of spindle
Nuclear envelope starts to break up

24. Mitosis Details: Transition to Metaphase
Spindle forms
Spindle microtubules become attached to the two sister chromatids of each chromosome

25. Mitosis Details: Metaphase
All chromosomes are lined up at the spindle equator
Chromosomes are maximally condensed

26. Mitosis Details: Anaphase
Sister chromatids of each chromosome are pulled apart
Once separated, each chromatid is a chromosome

27. Telophase Chromosomes de-condense
Two nuclear membranes form, one around each set of unduplicated chromosomes
Telophase

28. Results of Mitosis
Two daughter nuclei
Each with same chromosome number as parent cell
Chromosomes in unduplicated form

29. Mitosis Details - Result
Mitosis is then followed by Cytokinesis.
Final Result:
2 identical offspring cells that have the diploid chromosome number and the same genetic information as the original parent cell.

30. Mitosis Details (cont.)
Abnormalities:
Cancer: uncontrolled cell division

31. Meiosis Details
Chapter 9

32. Sexual Reproduction Involves Meiosis Gamete production Fertilization
Produces genetic variation among offspring

33. Sexual Reproduction Shuffles Alleles
Through sexual reproduction, offspring inherit new combinations of alleles, which leads to variations in traits
This variation in traits is the basis for evolutionary change

34. Factors Contributing to Variation Among Offspring
Crossing over during prophase I
Random alignment of chromosomes at metaphase I
Random combination of gametes at fertilization

35. Gamete Formation Gametes are sex cells (sperm, eggs)
Arise from germ cells
ovaries
anther
testes
ovary

36. Meiosis: Phases and Events
Two consecutive nuclear divisions
Meiosis I
Meiosis II
DNA is NOT duplicated between divisions
Four haploid nuclei are formed

38. Stages of Meiosis Meiosis I Prophase I Metaphase I Anaphase I
Telophase I
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II

39. Meiosis I - Stages
Prophase I
Metaphase I
Anaphase I
Telophase I

40. Prophase I
Each duplicated, condensed chromosome pairs with its homologue
Homologues swap segments = Crossing Over
Each chromosome becomes attached to microtubules of newly forming spindle

41. Crossing Over Each chromosome becomes zippered to its homologue
All four chromatids are closely aligned = tetrad
Non-sister chromosomes exchange segments

42. Meiosis I Each homologue in the cell pairs with its partner,
then the partners
separate

45. Effect of Crossing Over
After crossing over, each chromosome contains both maternal and paternal segments
Creates new allele combinations in offspring

46. Metaphase I Chromosomes are pushed and pulled into the middle of cell
Sister chromatids of one homologue orient toward one pole, and those of other homologue toward opposite pole
The spindle is now fully formed

47. Anaphase I Homologous chromosomes segregate(separate) from each other
The sister chromatids of each chromosome remain attached

48. Telophase I & Cytokinesis
The chromosomes arrive at opposite poles
The cytoplasm divides
There are now two haploid cells
This completes Meiosis I

50. Meiosis II - Stages
Prophase II
Metaphase II
Anaphase II
Telophase II

51. Prophase II
Microtubules attach to the kinetochores of the duplicated chromosomes
Motor proteins drive the movement of chromosomes toward the spindle’s equator

52. Metaphase II
All of the duplicated chromosomes are lined up at the spindle equator, midway between the poles

53. Anaphase II
Sister chromatids separate to become independent chromosomes
Motor proteins interact with microtubules to move the separated chromosomes to opposite poles

54. Telophase II & Cytokinesis
The chromosomes arrive at opposite ends of the cell
A nuclear envelope forms around each set of chromosomes
The cytoplasm divides
There are now four haploid cells

58. Random Alignment
Either the maternal or paternal member of a homologous pair can end up at either pole
The chromosomes in a gamete are a mix of chromosomes from the two parents

59. Possible Chromosome Combinations
As a result of random alignment, the number of possible combinations of chromosomes in a gamete is: 2n
(Humans = 8,388,608!!!)
(n is number of chromosome types)

60. Possible Chromosome Combinations1 2 3
Possible Chromosome Combinations or or or

61. Results of Meiosis Meiosis Four haploid cells produced
Differ from parent and one another

62. Abnormalities
Nondisjunction: Chromosome pairs fail to separate during Meiosis
Causes Chromosomal abnormalities – extra or missing chromosmes
Ex. Down Syndrome

63. Spermatogenesis secondary spermatocytes (haploid) spermato-
gonium (diploid male reproductive cell)
primary spermatocyte (diploid)
spermatids (haploid)
Mitosis I,
Cytoplasmic division
Meiosis II,
Cytoplasmic division
Growth

64. Oogenesis three polar bodies haploid) first polar body haploid)
oogonium (diploid reproductive cell)
primary oocyte (diploid)
secondary oocyte haploid)
ovum (haploid)
Mitosis I,
Cytoplasmic division
Meiosis II,
Cytoplasmic division
Growth

65. Fertilization Male and female gametes unite and nuclei fuse
Fusion of two haploid nuclei produces diploid nucleus in the zygote
Which two gametes unite is random
Adds to variation among offspring

66. Mitosis & Meiosis Compared
Functions
Asexual reproduction
Growth, repair
Occurs in somatic cells
Produces clones
Meiosis
Function
Sexual reproduction
Occurs in germ cells
Produces variable offspring