1. Cell Reproduction
Chapter 19

2. Understanding Cell Division
What instructions are necessary for inheritance?
How are those instructions duplicated for distribution into daughter cells?
By what mechanisms are instructions parceled out to daughter cells?

3. Reproduction
Parents produce a new generation of cells or multicelled individuals like themselves
Parents must provide daughter cells with hereditary instructions, encoded in DNA, and enough metabolic machinery to start up their own operation

4. Eukaryotic Cell Division
Mitosis, division of cytoplasm
Body growth and tissue repair
Meiosis, division of cytoplasm
Formation of gametes, sexual reproduction

5. Chromosome A DNA molecule & attached proteins
Duplicated in preparation for mitosis
one chromosome (unduplicated)
one chromosome (duplicated)

6. Chromosome Number Sum total of chromosomes in a cell Somatic cells
Chromosome number is diploid (2n)
Two of each type of chromosome
Gametes
Chromosome number is haploid (n)
One of each chromosome type

7. Human Chromosome Number
Diploid chromosome number (n) = 46
Two sets of 23 chromosomes each
One set from father
One set from mother
Mitosis produces cells with 46 chromosomes--two of each type

8. Cell Cycle Cycle starts when a new cell forms
During cycle, cell increases in mass and duplicates its chromosomes
Cycle ends when the new cell divides

9. Interphase Usually longest part of the cycle Cell increases in mass
Number of cytoplasmic components doubles
DNA is duplicated

10. Stages of Interphase G1 S G2 Interval or gap after cell division
Time of DNA synthesis (replication) G2
Interval or gap after DNA replication

11. HeLa Cells Line of human cancer cells that can be grown in culture
Descendants of tumor cells from a woman named Henrietta Lacks
Lacks died at 31, but her cells continue to live and divide in labs around the world

12. Mitosis Period of nuclear division
Usually followed by cytoplasmic division
Four stages:
Prophase
Metaphase
Anaphase
Telophase

13. Stages of Mitosis
Prophase
Metaphase
Anaphase
Telophase

14. Early Prophase - Mitosis Begins
Duplicated chromosomes begin to condense

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

16. Transition to Metaphase
Spindle forms
Spindle microtubules become attached to the two sister chromatids of each chromosome

17. Metaphase All chromosomes are lined up at the spindle equator
Chromosomes are maximally condensed

18. Anaphase Sister chromatids of each chromosome are pulled apart
Once separated, each chromatid is a chromosome

19. Telophase Chromosomes decondense
Two nuclear membranes form, one around each set of unduplicated chromosomes

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

21. Cytoplasmic Division
Usually occurs between late anaphase and end of telophase

22. Effects of Irradiation
Ionizing radiation
May break apart chromosomes, alter genes
Large doses destroy cells
Small doses over long time less damaging
Medical X rays, radiation therapy

23. Irradiated Food
Foods irradiated to kill microorganisms, prolong shelf life
Not radioactive
No evidence it is a health risk
Critics worry about selecting for radiation-resistant strains, changes in food composition

24. Control of the Cycle
Once S begins, the cycle automatically runs through G2 and mitosis
The cycle has a built-in molecular brake in G1
Cancer involves a loss of control over the cycle, malfunction of the “brakes”

25. Stopping the Cycle Some cells normally stop in interphase
Neurons in human brain
Arrested cells do not divide
Adverse conditions can stop cycle
Nutrient-deprived amoebas get stuck in interphase

26. Organization of Chromosomes
DNA
one nucleosome
DNA and proteins
arranged as cylindrical fiber
histone

27. The Spindle Apparatus Consists of two distinct sets of microtubules
Each set extends from one of the cell poles
Two sets overlap at spindle equator
Moves chromosomes during mitosis

28. Sexual Reproduction Chromosomes are duplicated in germ cells
Germ cells undergo meiosis and cytoplasmic division
Cellular descendants of germ cells become gametes
Gametes meet at fertilization

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

30. Meiosis: Two Divisions
Two consecutive nuclear divisions
Meiosis I
Meiosis II
DNA is not duplicated between divisions
Four haploid nuclei form

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

32. Meiosis II
The two sister chromatids of each duplicated chromosome are separated from each other
two chromosomes
(unduplicated)
one chromosome
(duplicated)

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

34. 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

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

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

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

38. Crossing Over Each chromosome becomes zippered to its homologue
All four chromatids are closely aligned
Nonsister chromosomes exchange segments

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

40. Random Alignment
During transition between prophase I and metaphase I, microtubules from spindle poles attach to kinetochores of chromosomes
Initial contacts between microtubules and chromosomes are random

41. 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

42. Possible Chromosome Combinations
As a result of random alignment, the number of possible combinations of chromosomes in a gamete is: 2n
(n is number of chromosome types)

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

44. 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

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

46. 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

47. Prophase vs. Prophase I Prophase (Mitosis) Prophase I (Meiosis)
Homologous pairs do not interact with each other
Prophase I (Meiosis)
Homologous pairs become zippered together and crossing over occurs

48. Anaphase, Anaphase I, and Anaphase II
Anaphase I (Meiosis)
Homologous chromosomes are separated from each other
Anaphase/Anaphase II (Mitosis/Meiosis)
Sister chromatids of a chromosome are separated from each other

49. Results of Mitosis and Meiosis
Two diploid cells produced
Each identical to parent
Meiosis
Four haploid cells produced
Differ from parent and one another