1. Cellular Reproduction and Chromosomes
Cell Cycle, Mitosis, Meiosis and Gene Expression

2. Cell Cycle
Cells reproduce through a continuous sequence of growth and division known as the cell cycle
Interphase – cells are making new molecules and DNA is copied in a process called DNA replication.
Interphase broken into 3 steps:
G1 – Gap 1 involves metabolic activities
S – Synthesis involves DNA replication
G2 – Gap 2 is preparation for cell division

3. Cell Cycle
Timing of each phase can vary among different types of cells.
Organ cell vs. skin cell
Parent cell divides to create two new daughter cells (somatic cells have 46 chromosomes)
Purpose of Mitosis
Growth
Regeneration of Damaged Tissue
Maintenance of the Body

4. Chromosomes
Hold the genetic information needed to maintain the cell and make new copies of the cell
Made up of two sister chromatids which are held together with a centromere.
Chromatids are exactly identical to one another

5. Phases of Mitosis
Several events must happen to ensure that as a cell divides, the genetic material inside is properly shared between each new daughter cell.
Phase order: PMAT & C
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
p. 144 figure 4

6. Prestep INTERPHASE Preparation for division
The cell duplicates it’s genetic material (called chromatin) and creates two identical sister chromatids, joined by an object known as a centromere.

7. Mitosis
Prophase
chromatin, which is DNA and proteins, condenses and becomes visible
Nuclear membrane and nucleolus disappear
Centrioles made up of microtubules migrate to opposite poles of the cell
Spindle fibres start to form between the two centrioles

8. Mitosis Metaphase Anaphase Spindle fibres attach to centromere
Chromosomes line up on the cell’s equator (equatorial plate)
Anaphase
Centromere splits and chromatids are pulled to opposite poles of the cell

9. Mitosis Telophase Cytokinesis Chromatids reach the two opposite poles
At this time each chromatid is considered a single non-replicated chromosome
Chromosomes unwind and become less visible
Cytokinesis
Actual cell division
Spindle fibres disappear, nucleolus reappears, nuclear membrane and in plant cells a new cell wall is formed

10. Meiosis, Chromosomes and Heredity

11. Meiosis and Chromosomes
A zygote contains chromosomes from both parents
Meiosis only occurs in reproductive organs and produces cells known as gametes (eggs or sperm) which are haploid (n).
All other cells (somatic) are diploid (2n) and contain two copies of each type of chromosome.

12. Chromosomes
The first part of meiosis reduces the chromosome number from diploid (2n) to haploid (n) known as reduction division.
Each sperm or egg cell contains 22 autosomes and one sex chromosome (X or Y)
The autosomes control almost all of the functions of the individual and the sex chromosomes determine the sex of the individual.

13. Reduction Division

14. Meiosis
Almost the same as mitosis however there are two sequences of each of the phases.
Interphase – chromosomes replicate
Meiosis I - reduction division
Prophase I, Metaphase I, Anaphase I, and Telophase I are all part of.
Meiosis II - identical to mitosis.
Prophase II, Metaphase II, Anaphase II and Telophase II

15. Meiosis
Prophase I – homologous chromosomes pair which make up four chromatids called a tetrad.
23 pairs of homologous chromosomes, one copy of each pair came from each parent
Crossing over - recombination of genes
Page 154 figure 6

16. Meiosis
Metaphase I – spindle fibres attach to the centromere of each chromosome
Anaphase I - Homologous chromosomes are separated independently
The centromere does not split

17. Meiosis
Telophase I
Needs to occur however can be a lengthy or short process
Short  cell division goes directly to meiosis II
Lengthy  chromosomes uncoil and nuclear membrane is formed (replication does not need to occur)

18. Meiosis Each cell beginning meiosis II is haploid
Each cell at the end of meiosis II is also haploid although they are called gametes or spores.
Meiosis II is exactly the same as Mitosis however there are only 23 chromosomes to split at the centromere in each cell instead of 46 as in the somatic cells
Gametogenesis – process of creating sperm and eggs.

19. Gamete Formation - Male
Spermatogenesis – male gamete formation
A diploid germ cell (spermatogonium) undergoes the meiosis process to create 4 haploid cells
Following meiosis II, cytoplasm lost and a tail develops

20. Gamete Formation Oogenesis – female gamete formation
Diploid germ cell (oogonium) undergoes meiosis to create 1 haploid cell –primary oocyte is much larger than polar bodies
After meiosis II, the cytoplasm is again unequally divided and only one cell is viable as a sex cell, the ovum (egg cell)

21. Genetic Variation Dependent on 2 factors:
Crossing over – occurs during prophase I and the number of which is determined by the chromosome size (usually 2 or 3 cross overs per chromosome).
Random Segregation – how each pair of homologous chromosomes line up during metaphase I is also extremely important as that determines which pole the chromosomes will go to.
These two factors work together and are the basis behind genetic recombination

22. Genetic Variation

23. Diploid (2n) vs Haploid (1n)