IN EUKARYOTES, HERITABLE INFORMATION IS PASSED TO THE NEXT GENERATION VIA PROCESSES THAT INCLUDE THE CELL CYCLE AND MITOSIS OR MEIOSIS PLUS FERTILIZATION. Essential knowledge 3.A.2:

Think-Pair-Share  How many cells are in your body?  How were those cells produced from a single cell called a zygote?  How does the genetic information in one of your body cells compare to that found in other body cells?  What are some advantages of asexual reproduction in plants?  What is the importance of the fact that DNA is replicated prior to cell division?  How do chromosomes move inside a cell during division?  How is the cell cycle controlled? What would happen if the control were defective?

Why do cell divide?  Reproduction – mitosis plays a role in asexual reproduction  Growth  Repair  Mitosis followed by cytokinesis produces two genetically identical daughter cells.

. Interphase consists of three phases: growth, synthesis of DNA, preparation for mitosis.

 Mitosis alternates with interphase in the cell cycle.  When a cell specializes, it often enters into a stage where it no longer divides, but it can reenter the cell cycle when given appropriate cues.  Nondividing cells may exit the cell cycle; or hold at a particular stage in the cell cycle.

Mitosis

Mitosis passes a complete genome from the parent cell to daughter cells. Top 4 list to remember about mitosis:  1. Mitosis occurs after DNA replication.  2. Mitosis followed by cytokinesis produces two genetically identical daughter cells.  3. Mitosis plays a role in growth, repair, and asexual reproduction  4. Mitosis is a continuous process with observable structural features along the mitotic process. Replication  alignment  separation

Animal Mitosis

Binary Fission  Bacteria may point to the evolutionary history of mitosis

The cell cycle is a complex set of stages that is highly regulated with checkpoints, which determine the ultimate fate of the cell.  The cell cycle is directed by internal controls or checkpoints. Internal and external signals provide stop-and-go signs at the checkpoints.  examples: Mitosis-promoting factor (MPF) Action of platelet-derived growth factor (PDGF) Cyclins and cyclin-dependent kinases control the cell cycle.

Control Systems  The distinct events of the cell cycle are directed by a distinct cell cycle control system.  A checkpoint in the cell cycle is a critical control point where stop and go signals regulate the cycle.  Three major checkpoints are found in the G 1, G 2, and M phases.

Control Systems  Rhythmic fluctuations in the abundance and activity of control molecules pace the cell cycle.  Some molecules are protein kinases that activate or deactivate other proteins by phosphorylating them.  The levels of these kinases are present in constant amounts, but these kinases require a second protein, a cyclin, to become activated.  Levels of cyclin proteins fluctuate cyclically.  The complex of kinases and cyclin forms cyclin- dependent kinases (Cdks).

Cancer cells have escaped from cell cycle control  Cancer cells do not stop dividing when growth factors are depleted either because they manufacture their own, have an abnormality in the signaling pathway, or have a problem in the cell cycle control system.  If and when cancer cells stop dividing, they do so at random points, not at the normal checkpoints in the cell cycle.

 The abnormal behavior of cancer cells begins when a single cell in a tissue undergoes a transformation that converts it from a normal cell to a cancer cell.  Normally, the immune system recognizes and destroys transformed cells.  However, cells that evade destruction proliferate to form a tumor, a mass of abnormal cells.

Meiosis

Quick Comparison  Mitosis After cell division the daughter cell are genetically the same as the parent cell. They have basically cloned themselves. The chromosome numbers are also the same. 2n to 2n  Meiosis After cell division the daughter cells are genetically different than the parent cell. The cell divides twice. The daughter cell have half the number of chromosomes as the parent. 2n to 1n

What makes meiosis different?  During meiosis, homologous chromosomes are paired, with one homologue originating from the maternal parent and the other from the paternal parent.  Orientation of the chromosome pairs is random with respect to the cell poles.  Separation of the homologous chromosomes ensures that each gamete receives a haploid (1n) set of chromosomes composed of both maternal and paternal chromosomes.

Crossing Over  During meiosis, homologous chromatids exchange genetic material via a process called “crossing over,” which increases genetic variation in the resultant gametes.  Crossing over helps ensure genetically different offpsring

Meiosis forms haploid sperm and egg

Fertilization  Fertilization involves the fusion of two gametes, increases genetic variation in populations by providing for new combinations of genetic information in the zygote, and restores the diploid number of chromosomes.

How does meiosis and sexual reproduction ensure genetic diversity? Humans as an example: #1 Random assortment of chromosomes #2 Crossing Over #3 Random Fertilization