1. Section 8-1 Chromosomes Section 8-2 Cell Division Section 8-3 Meiosis
Cell Reproduction
Section 8-1 Chromosomes
Section 8-2 Cell Division
Section 8-3 Meiosis

2. Section 8-1 Chromosomes Chromosomes are super coiled DNA strands
Chromosome Structure
Chromosomes are super coiled DNA strands
Rod-like structures made of DNA and proteins.
Appear as darkened structures in the nucleus

3. How are chromosomes formed?
DNA wraps tightly around proteins called histones
DNA coils in a specific way to produce the structure of a chromosome

5. Chromosome Numbers Two types of Chromosomes
Autosomes – all chromosomes that DO NOT determine the sex of an organism
Sex Chromosome – determines the sex of an organism
Males – XY
Females - XX

6. Homologous Chromosomes
Same size, shape and carry genes for the same traits
You get one copy of each chromosome from each parent

7. Karyotype

8. Haploid & Diploid Cells
Diploid (2n)– Cells with 2 sets of chromosomes (normal cells)
Humans have 22 autosome pairs & 1 pair of sex chromosomes (46 total)
Haploid (n) – cells with 1 set of chromosomes
In humans the ONLY cells that are haploid are reproductive cells (sperm & egg)

10. Section 8-2 Cell Division
Prokaryotes
Binary fission – prokaryotic cell division, when a cell produces TWO offspring cells
DNA Copied
Cell Divides
Two identical

11. Eukaryotic Cell Division
Cytoplasm and nucleus divides
Two types of cell division
Mitosis – cells with genetic material identical to the parent cell
Occurs in unicellular organisms
Occurs in multicellular organisms to add cells to tissues and organs
Meiosis – cells with a reduced chromosome number

13. Mitosis vs. Binary Fission
One diploid cell being copied
Results in two identical diploid cells
Occurs in eukaryotic organisms
One haploid cell being copied
Results in two identical haploid cells
Occurs in prokaryotic organisms

14. MITOSIS
BINARY FISSION

15. Cell Cycle Repeating set of events that make up the life of a cell
Cell Division is ONLY a part of the cell cycle
2 phases - Mitosis & Cytokinesis
Interphase – time between cell divisions
3 phases - G1, S, G2

16. Interphase
G1 (growth 1) - new cells are growing before DNA replication
S (synthesis) - After cells reach mature size, they replicate the DNA
G2 (growth 2) – cells divide the organelles and prepare for mitosis

17. Mitosis
4 Phases
Prophase
Metaphase
Anaphase
Telophase
(PMAT)

18. Prophase First phase of mitosis
DNA coils and shortens into chromosomes (a)
Chromosomes attach at the centromere
Outside the nucleus centrioles (b) form
Spindle fibers (c) form which help to divide chromosomes

19. Metaphase Chromosomes are easier to identify (completely condensed)
Second phase of mitosis
Chromosomes are easier to identify (completely condensed)
Chromosomes are lined up in the middle of the cell

20. Anaphase Chromatids of each chromosome separate at the centromere
Third phase of mitosis
Chromatids of each chromosome separate at the centromere
Chromatids move toward the poles of the cell (centromere first)

21. Telophase Final phase of mitosis
Chromosomes reach opposite ends, the nuclear envelope reforms
Chromosomes begin to uncoil
Nucleolus begins to form in each new cell

22. Cytokinesis Sometimes considered a part of telophase
The division of the cytoplasm
Animal Cells – Cell membranes pinch INWARD at the cleavage furrow
Plant Cells – Cell forms a “cell plate” between the new cells before cell wall forms

23. Identify the phase of mitosisB D C

26. Section 8-3 Meiosis Cells prepare for meiosis by undergoing interphase
Cells begin meiosis with a duplicate set of chromosomes
Cells then divide TWICE to reduce the chromosome number

27. Meiosis I - Very closely resembles mitosis
Prophase I – DNA coils, spindle fibers form
Homologous chromosomes pair – SYNAPSIS
TETRAD – the pair of homologous chromosomes
Metaphase I – tetrads line up at the middle
Anaphase I – chromosomes are pulled to the poles
Telophase I – chromosomes are at opposite poles AND cytokinesis begins

29. Events DURING Meiosis I
Crossing Over
Occurs during Prophase I
When portions of chromatids break off and re-attach on homologous chromosomes
Permits the exchange of genetic material
Independent Assortment
Occurs during Anaphase I
The random separation of the genetic material
Results in genetic recombination

30. Crossing Over

31. Meiosis 2 – Reducing Chromosome Number
DNA IS NOT COPIED BEFORE MEIOSIS II
Prophase II – Spindle fibers form; move chromosomes
Metaphase II – chromosomes line up at the middle
Anaphase II – chromatids SEPARATE; moves to poles
Telophase II – nuclear membranes form around chromosomes
Cytokinesis II – cytoplasm divides creating 4 cells w/ ½ chromosome number

33. In animals – meiosis produced haploid reproductive structures
Formation of Gametes
In animals – meiosis produced haploid reproductive structures
Occurs in the testes and ovaries
Spermatogenesis – meiosis in males (testes)
Produces spermatids
Oogenesis – meiosis in females (ovaries)
Produces 1 egg and 3 polar bodies
Polar bodies degenerate

35. Reproduction
Asexual reproduction – production of offspring from ONE parent
Does not involve the union of sperm and egg
Offspring is genetically identical to the parent
Sexual reproduction – production of offspring using 2 parents
Meiosis
Union of sperm and egg