1. CH 8: The Cellular Basis of Reproduction and Inheritance

2. Methods of Reproduction
Asexual reproduction
Chromosomes are duplicated and cell divides
One copy of each chromosome is placed in each cell
Each “daughter” cell is genetically identical to the parent and the other daughter
Type of eukaryotic cellular division required: mitosis
Advantage = fast and convenient
Disadvantage = very little genetic variation

3. Methods of Reproduction Sexual reproduction
Offspring inherit DNA from both of their parents
Type of eukaryotic cellular division required: meiosis
Offspring can show great variation
Advantage = lots of genetic variation
Disadvantage = metabolically expensive

4. Prokaryotic cells reproduce asexually
by a type of cell division called binary fission
The circular DNA molecule replicates to form 2 chromosomes
The chromosome copies move apart
The cell elongates
The plasma membrane grows inward, dividing the parent into two daughter cells 
Colorized TEM 32,500

5. Prokaryotic
chromosome
Plasma
membrane
Cell wall
Duplication of chromosome
and separation of copies
Continued elongation of the
cell and movement of copies
Division into
two daughter cells

6. Eukaryotic Asexual Reproduction
Mitosis:
Purpose:
Asexual reproduction in single celled organisms
Growth and repair in multicelled organisms
An exact copy of the cell’s DNA is made*, the copies separated, and each copy is put in a new cell.
*Put another way…an exact copy of each chromosome is made

7. Mitosis Mitosis involves one cellular division.
1 cell  2 cells (called daughter cells)
Daughter cells are genetically identical
Chromosome number does not change.

8. Eukaryotic Chromosome condensed form
Sister chromatids have identical DNA
Centromere
Kinetechore on centromere provides binding site for microtubules
Sister chromatids

9. Eukaryote Chromosome Structure
Histone core is made up of 8 proteins
A nucleosome is 2 wraps of DNA around a histone core
Histone core shown in greater detail, see page 212

10. Cell Cycle
Cell cycle describes the “life cycle” of a cell- Cell cycle is tightly controlled G1
S Interphase G2
Mitotic Phase
Mitosis
Prophase, metaphase, anaphase, telophase
Cytokinesis

11. Mitosis
Mitosis = division of the cell’s DNA and nucleus in a eukaryotic cell
Cytokinesis = division of the cytoplasm (cell)
Mitosis occurs in somatic cells such as….

12. Cell Cycle

13. Cell Cycle Interphase G 1 - period of cell growth S - DNA synthesis
An exact copy is made of each chromosome
Copies are joined at the ________
G 2 – cell continues to grow and prepares to divide
e.g. centrioles duplicate in animal cells

14. Control of the Cell Cycle - Checkpoints
G1 Checkpoint
GO SIGNAL
Cell Completes Cell Cycle
Checks Cell Size, Organelles, Nutrition
STOP SIGNAL
Waits to Grow Larger
Control of the Cell Cycle - Checkpoints
M Checkpoint
G2 Checkpoint
Chromosomes Aligned?
DNA Replicated?
Spindle Fibers Attached?
Cell Division Machinery OK?

15. Mitosis
Mitosis (division of nucleus/chromosomes) follows interphase – see pages 130/131
4/5 phases
Prophase,Prometaphase
Metaphase
Anaphase
Telophase (and cytokinesis)

16. Prophase Chromosomes condense, become visible under microscope
Centriole pairs* move towards poles (animal only)
Nucleoli disappear
*centriole pair = centrosome

17. Prometaphase Transition from prophase to metaphase
Nuclear envelope breaks up and forms vesicles
Microtubules arranged as spindle fibers attach the kinetechore on the centromere of each sister chromatid to opposite poles
Attach to centrioles in animal cells

18. Plant Prometaphase Prometaphase in a plant cell
Chromosomes are visible
Nuclear envelope is breaking down
Spindle fibers cannot be seen in this micrograph.

19. Metaphase Spindle microtublules push and pull chromo to middle of cell
Centromeres line up across the middle of the cell
Microtubules running pole to pole elongate the cell
Not visible in this micrograph
Animal Metaphase

20. Plant Metaphase
Chromosomes tend to be “messier” in plant metaphase

21. Anaphase Sister chromatids separate at the centromere
MT* pull sister chromatids to opposite poles
MT continue to elongate cell
This also helps to separate chromatids
* MT = microtubules
Animal anaphase

22. Plant Anaphase
Separated sister chromatids (daughter chromosomes) clearly visible

23. Telophase Telophase starts when chromatids reach poles
Goal is to make 2 new nuclei
Chromo. unwind
Nucleoli reappear
Nuclear envelope reforms from vesicles
Animal cell shown

24. Cytokinesis Cytokinesis – division of cytoplasm
Begins during telophase
Different in plant and animal cells

25. Animal Cytokinesis
Microfilaments wrap around the center of the cell and then contract
Creates cleavage furrow
Cell “squeezed” in 2
Page 132

26. Plant Cytokinesis
Vesicles containing cell wall material line up across middle of cell
Vesicles merge and form cell plate
Cell plate grows until it divides the cell in 2
Cell plate

27. MITOSIS Interphase Prophase Metaphase Anaphase Telophase Cytokenesis
Is this a plant or an animal cell?

28. Mitosis Review Comparison Plant and Animal Mitosis Mitosis
Animal Cell Mitosis
Plant Cell Mitosis

29. Meiosis Meiosis is needed for sexual reproduction
Purpose of meiosis is to create gametes
Egg and sperm in humans
Needed for sexual reproduction
Gametes have only one copy of each type of chromosome
Occurs in germ cells
Ovaries and testes of humans

30. Related Terms
Diploid = 2 copies of each type of chromosome present (2N)
One copy came from mom’s egg and the other from dad’s sperm
Human diploid number = 46 (also say 2N = 46)
Haploid = 1 copy of each type of chromosome present (N)
Human haploid number = 23 (N = 23)
Gametes are haploid

31. Overview Meiosis
Meiosis separates homologous chromosomes and produces cells with a single set of chromosomes
Homologous Chromosomes: pair of chromosomes with genetic information about the same traits, page 136

32. Human Karyotype Homologous Chromosomes

33. Meiosis
The process of meiosis requires 2 cellular divisions – page 137
One division to separate homologous chromosomes
Second division to separate duplicated chromosomes

34. MEIOSIS MEIOSIS I Begins With: Functions: Duplicated Chromosomes
Homologous Pair
Begins With:
Duplicated Chromosomes
Diploid (2N) Cells
Meiosis 1
Functions:
Separate Homologous Chromosomes
Go From Diploid (2N) to
Haploid (N)

35. MEIOSIS II Begins With: Function: Duplicated Chromosomes
Haploid (N) cells
Function:
Meiosis II
Separate Sister Chromatids
Creates gametes

36. 2N = 2
Crossing over occurs in meiosis I
Homologous chromosomes separate in meiosis I
2 cells, N = 1 for each
Sister chromatids separate in meiosis II
4 cells, N = 1 for each.
Chromosomes are different due to crossing over

37. Meiosis I Prophase I Duplicated chromosomes form tetrads
Cell is diploid
Chromosomes are duplicated
Duplicated chromosomes form tetrads
Tetrad = pair of homologous chromosomes
Crossing over occurs
Exchange of genetic material between homologous chromosomes

38. CROSSING OVER Exchange of genetic material
between Homologous Chromosomes M F
During Prophase I
occurs at CHIASMA
Meiosis 1
Meiosis 2
Produces new genetic combinations
--Chromosomes with both
Maternal & Paternal components
Gametes

39. Meiosis I Prophase I, continued Chromosomes condense (super-coil)
Centrioles move towards opposite poles (animal only)
Spindle fibers begin to assemble
Nuclear envelope breaks down (always signals end of a prophase )

40. Meiosis I
Metaphase I
Spindle fibers push and pull the tetrads to the middle of the cell.
Spindle fibers attach each chromosome of the pair to one pole

41. Meiosis I
Anaphase I
Homologous chromosomes are separated and pulled to opposite poles by the spindle fibers
Microtubules running pole to pole lengthen and elongate the cell

42. Meiosis I Telophase I and Cytokinesis
Chromosomes reach the poles – still duplicated
Cell divides in two
Animal cells - cleavage furrow squeezes cell in two
Plant cells – cell plate divides cell in two
Generally, the nucleus does not reform

43. At the end of Meiosis I Homologous chromosomes have been separated
Chromosomes are still duplicated
Sister chromatids are no longer identical due to crossing over
Chromosome number has been cut in half (to haploid number)
Count centromeres to count chromosomes

44. 2N = 2
Crossing over occurs in meiosis I
Homologous chromosomes separate in meiosis I
2 cells, N = 1 for each
Sister chromatids separate in meiosis II
4 cells, N = 1 for each.
Chromosomes are different due to crossing over

45. Meiosis II Prophase II – in each cell
Centriole pairs separate and move to opposite poles (animal only)
Spindle fibers attach to kinetechore (centromere) of each chromosome
Remember chromosomes are still duplicated
Notice that each chromo is attached to both poles (as in mitosis)

46. Meiosis II Metaphase II
Spindle fibers push and pull duplicated chromo. To the center of the cell

47. Metaphase II

48. METAPHASE I – tetrads line up across the center of the cell
METAPHASE II – duplicated chromosomes line up

49. Anaphase II Spindle fibers separate the sister chromatids
One copy of each chromosome moves to each pole
Microtubules running pole to pole lengthen and elongate the cell

50. Telophase II Telophase II and Cytokinesis Meiosis web link
Nucleus reforms in each cell (4 cells in total)
Cytoplasm divides
Meiosis web link

51. Meiosis Two cellular/nuclear divisions
1st division separates homologous chromosomes (each in its duplicated state)
2nd division separates duplicated chromosomes
1 cell with 2N chromo  2 cells with N duplicated chromo 4 cells with N chromo

52. Meiosis End result of meiosis 4 cells are made
Each cell has the haploid number of chromo.
One copy of each type of chromo
No two gametes are identical due to:
independent assortment of homologous chromosomes (page 141)
crossing over during meiosis I

54. Cell Division Summary
Page 140 provides a summary of the 2 types of cellular division.
Given a picture of a phase of mitosis or meiosis you should be able to:
Identify the phase and division type
Label as appropriate: spindle fibers, centrioles, sister chromatids, homologous chromosomes, centromere/kinetechore, nuclear envelope…