1. Important terms in eukaryotic cell division
Chromosome = threadlike structures that are composed of DNA + protein
replication = process whereby DNA is identically copied (before cell division)
mitosis = division of the nucleus
cytokinesis = division of the cytoplasm
chromatin = DNA + protein complex that is thin and fibrous; it will condense into distinct chromosomes during cell division

2. Why do cells divide? Reproduction Replacement of damaged cells
Growth of new cells

3. Why Replication?
DNA and protein molecules that make up chromosomes are spread through the nucleus
At the beginning of cell division, the chromosomes condense into compact visible structures (chromosomes)
Before cell division, each chromosome is replicated (copied)
Each chromosome is made up of 2 identical “sister” chromatids held together by a centromere

4. Chromosome = condensed chromatin
Chromatin= condensed DNA
DNA= molecule that holds the blueprints for a cell

5. Chromosomes
Genetic information is passed on from one generation to the next through chromosomes
Every organism has a specific number of chromosomes (ex: humans = 46, carrots = 18)
Chromosomes are not visible in most cells except in cell division

6. Interphase 90% of cell cycle is spent in this phase
G1 = first growth phase
S = synthesis phase, DNA synthesis occurs here (cell performs its job)
G2 = second growth phase

7. Prophase Metaphase Anaphase Telophase
Mitosis is one, continuous event, but it can be described as happening in 4 phases:
Prophase
Metaphase
Anaphase
Telophase

8. PROPHASE In the Nucleus: Nucleoli disappear
Chromosome fibers condense into discrete chromosomes
Each chromosome consists of 2 sister chromatids joined at the centromere

9. PROPHASE continued… In the Cytoplasm: mitotic spindle begins to form
spindle consists of microtubules arranged between the centrioles
centrioles move apart due to lengthening of microtubules

10. PROPHASE

11. METAPHASE A.) chromosomes line up in the center of the cell;
B.) spindle fibers connect from the poles (end) of the spindle to the centromere of each chromosome

12. METAPHASE

13. ANAPHASE
A.) centromeres split, causing the sister chromatids to separate, becoming individual chromosomes
B.) chromosomes are pulled apart to opposite ends of the cell
(the shape of the cell elongates into an elipse)

14. ANAPHASE

15. TELOPHASE A.) chromosomes uncoil into chromatin
B.) new nuclear envelope forms around the chromatin
C.) spindle breaks apart
D.) nucleolus reappears in each new nucleus

16. TELOPHASE

17. Finally… CYTOKINESIS
animal cells: cell membrane pinches in & divides (cleavage furrow)
plant cells: a cell plate forms (new cell wall)
**Begins before telophase has completed**

18. Identify the phase
Metaphase anaphase?

19. Identify the phase
cytokenisis

20. Identify the phase
metaphase

21. Identify the phase
anaphase

23. Meiosis

24. Meiosis
Specialized type of cell division that occurs when egg and sperm cells are formed
Although it appears much more complicated than mitosis, it is really just two divisions in sequence.

25. MEIOSIS I
Meiosis I, the first of the two divisions, is often called reduction division, since it is here that the chromosome number is reduced from 46 to 23.
*remember this must happen for us to get half our chromosomes from our dad and half from our mom!

26. INTERPHASE Interphase in meiosis is identical to interphase in mitosis
Meiotic division will only occur in cells associated with male (sperm) or female (egg) sex cells.

27. PROPHASE I
Prophase I is virtually identical to prophase in mitosis

28. METAPHASE I
In Metaphase I of Meiosis), the chromosome pairs are aligned on either side of the metaphase plate.
Here is where the first difference between mitosis and meiosis occurs
during this alignment that chromatid arms may overlap and temporarily fuse resulting in crossovers which are important in allowing for genetic variations
In Mitosis, all the chromosomes line up on the metaphase plate in no particular order.

30. ANAPHASE I
During Anaphase I the spindle fibers contract, pulling the homologous pairs away from each other and toward each pole of the cell.

31. TELOPHASE I Cleavage furrow is formed, followed by cytokinesis, but…
the nuclear membrane (envelope) usually is not reformed and the chromosomes do not disappear.
At the end of Telophase I, each daughter cell has a single set of chromosomes, half the total number in the original cell where the chromosomes were present in pairs.

32. MEIOSIS II
Meiosis II = a simple division of the two cells created in meiosis one.
Basically the process repeats to form two more cells with chromosomes different from the parent cell.

33. PROPHASE II
A new set of spindle fibers forms and the chromosomes begin to move toward the equator of the cell.

34. METAPHASE II
All the chromosomes in the two cells align with the metaphase plate.

35. ANAPHASE II The centromeres split
The spindle fibers shorten drawing the chromosomes toward each pole of the cell.

36. TELOPHASE II
Cleavage (the pinching in the cell membrane) is followed by cytokinesis
The nuclear membrane/envelope reforms
Total of four daughter cells, each with half the total number of chromosomes as the original cell.

37. In the case of male structures, all four cells will eventually develop into typical sperm cells.
In the case of female life cycles in “higher” organisms, three of the cells will typically abort, and only one haploid cell will develop into an egg cell

38. Differences between Meiosis and Mitosis
Mitosis produces somatic cells while meiosis produces gametes (egg and sperm)
Mitosis produces diploid cells (two copies of each chromosome) and meiosis produces haploid cells (one copy of each chromosome)
Mitosis produces two daughter cells while meiosis produces four daughter cells
Mitosis goes through one division while meiosis goes through two divisions