Sexual vs. asexual reproduction

2. Sexual vs. asexual reproduction • Asexual reproduction occurs by mitosis, it is a careful copying mechanism-meaning all offspring are always genetically identical to the parent • Sexual reproduction occurs by meiosis and brings enormous potential for genetic variability (but the variability will only occur before fertilization • In humans, there are 8,388,608 distinct distributions per gene

3. DNA Replication • DNA plays an important role in protein synthesis, but also in cell division • Cells must be able to divide in order the for organisms to grow, reproduce and repair itself • DNA is stored in the form of chromatin-long strands of DNA, jumbled up with proteins, that form a disorganized mess of genetic material • When the cell is ready to divide, the chromatin condenses to form chromosomes

4. Chromosomes • Chromosomes are the genetic information that is passed from one generation to the next • Made up of coiled DNA • Each organisms has its own specific number of chromosomes (humans have 46) • Chromosomes are not usually visible except during cell division

5. Chromosomes • A chromosomes’ identical copy of itself is called a chromatid • Each chromatid is attached at an area called a centromere (usually located at the center of the chromatid)

6. Chromosomes

7. Cell Types • Multicellularorganisms are made up of two kinds of cells: reproductive (sex cells) and somatic (body cells) • Reproductive cells have a single set, termed haploid (n) • Somatic cells have two sets, termed diploid (2n) • When the cell divides the chromosomes must be distributed between the new cells

8. Cell Cycle • The cell cycle is the sequence of stages through which a cell passes between one cell division and the next • There are two main stages: Interphase and Mitosis

9. Cell Cycle

10. Interphase • Interphase is the phase where the cell is performing normal cell functions such as protein synthesis and preparing for cellular division • During this phase a series of events (stages) must occur in order for the cell to grow and divide • The stages are G1, S1, G2 (cell growth, DNA replication, and preparation for mitosis via replication of organelles and increasing the amount of cytoplasm)

11. Interphase • Cells remain in interphase for long spans of their life • Once interphase is complete, then the cell will start to divide • First the cell will increase its size and produce new proteins and organelles • Then each chromosome is replicated • After the cell has completed interphase, cellular division will occur

12. Cellular Division • Organisms grow and divide because the cells divide and more cells are present-not because individual cells grow larger, this is called cellular division • Cellular division relies on DNA because it stores and transmit’s the hereditary (genetic) information from one generation to the next • Cells will only grow to a certain size because if they get too big, they will lose their ability to regulate their energy uses and waste production, also the cell’s DNA will not be able to keep up with the workload to keep the cell functioning

13. Cell Division • Before the cell gets too large, the cell will divide into two daughter cells • All of the cell’s organelles and genetic information will be duplicated before the cell divides • Each of the new daughter cells will have a complete set of genetic information • Cell division reduces the cell’s volume but not its size • It occurs in two stages: Mitosis and Cytokinesis

14. Mitosis • A type of cell division that generates two daughter cells with identical components of the mother cell • Associated with asexual reproduction-it only requires one parent cell • The division of the nucleus and thus the first stage • It is a continuous cycle that most cells will undergo • Occurs in most multi-cellular organisms (its called binary fission in unicellular organisms) • It is divided into four phases: Prophase, Metaphase, Anaphase, and Telophase (PMAT)

15. Mitosis

16. Prophase-Prepare • It is the longest stage of mitosis • Chromosomes thicken and become visible with a microscope • Nuclear membrane disintegrates • Centrioles(small cylindrical bodies) move to opposite ends of the cell • Spindle fibers (microtubules) grow from the centrioles to the chromosomes to help separate them

17. Prophase-Whitefish

18. Prophase-Onion

19. Metaphase-Middle • Chromosomes form pairs attached by centromeres and will align along the middle of the cell

20. Metaphase-Whitefish

21. Metaphase-Onion

22. Anaphase-Apart • The centromeres split which causes the chromosomes to separate back into individual chromatids • The chromatids will move to opposite poles being pulled apart by the spindle fibers

23. Anaphase-Whitefish

24. Anaphase-Onion

25. Telophase-Two • A nuclear envelope appears around each new set of chromosomes • The nucleolus reappears

26. Telophase-Whitefish

27. Telephase-Onion

28. Cytokinesis • Cyto-cell, kinesis-split • Material outside of the nucleus must also divide • Generally beings during telophase • This is when the actual cell divides to form two new cells

29. Cytokinesis • In animals, cytokinesis occurs when the cell membrane pinches in and divides • In plants, a cell plate forms across the middle of the cell which is then followed by the formation of cell walls on each side • Following cytokinesis, the cell returns to the period of interphase

30. Cell Growth • Cell growth is usually well controlled • Most of the time, cells are at different stages of cellular division throughout the body and divide at different rates • For example, blood cells grow and divide very rapidly whereas brain cells (neurons) do not • There are some instances of uncontrolled cell growth-Cancer

31. Cancer • It is a condition in which cells grow and reproduce at a rapid rate and do not respond to the usual controls (cyclins) that limit cellular growth • These large masses of cells are called tumors • When tumors form in the body, they can damage the surrounding tissues • If parts of the tumor breaks off into the body, the cancer can spread