Cell Division: Mitosis and Meiosis

Transcription

1 1 Cell Division: Mitosis and Meiosis Chromosomes are structures that contain material When Eukaryotes are not dividing, DNA and Proteins are in a mass called: When the cell divides, it condenses and becomes identifiable as individual Humans have chromosomes in their body or cells This is the normal number and these cells are called - noted as (2n) These cells undergo to replicate/divide Sex cells or have chromosomes which is half the number These cells are called, are noted as (n), and undergo Mitosis This is how unicellular cells reproduce; resulting in identical copies of the cell. In multicellular organisms it is the simple cell division necessary for: New cells can only come from pre-existing cells. Cells cannot get too big need surface area to volume ratio for transport & efficiency Mitosis ensures that all new cells get the proper number of: Cell Cycle the phases in the life of a cell Interphase and Cell Division Interphase occurs when the cell is: Longest phase in the cell cycle, divided into three stages G1 = Named for Gap 1 but the cell is really performing its function and Some cells stop in this stage and do not divide for example cells are needed to move on to each new level If they are not there, the cell will not move on and will not divide S = Named for or DNA Replication Chromosomes copy themselves so that: At the beginning of Interphase, each chromosome is made of 1 After Replication, each chromosome is made of They are called sister because they are: The 2 chromatids are connected by a G2 = Named for Gap 2 but the cell is getting ready to Store up proteins and ATP, replicate If there are no growth factors, some cells like muscle cells stay in this stage Cell Division Includes karyokinesis = division of the during Mitosis And cytokinesis = division of the during Cytokinesis

2 2 Stages of Mitosis Prophase Chromatin condenses around proteins so chromosomes are visible and disappear fibers form from the cell wall in plants and fungi and the in animal cells. In animal cells, the spindle apparatus radiates out from the centriole and is called an Prometaphase The attaches the centromere to the spindle fibers Metaphase The chromosomes align on the: Anaphase The centromeres divide resulting in daughter chromosomes made up of chromatid and centromere The spindle lengthens to push the poles of the cell further apart Telophase break down and reform The chromosomes relax into chromatin Each daughter cell has the number of chromosomes Cytokinesis occurs with and is the division of the In animal cells, actin filaments pull in the membrane between the cells, forming a: In plant cells, the golgi apparatus produces new cell wall called a: Bacteria do a similar but much more simple type of cell division called The circular DNA copies itself and the cell splits

3 3 Meiosis This is the process of making for sexually reproducing organisms They must be or. If not then the cells would in chromosome number with each generation when a sperm fertilizes an egg to make a Meiosis reduces the chromosome number from diploid to haploid in a special way to make sure the right chromosomes are passed on Each diploid cell has chromosomes, from the sperm and from the egg There are pairs of chromosomes, called 1 member of the pair is, 1 member of the pair is Each member of the pair has the gene that codes for the same genetic trait Eye color from Dad, Eye color from Mom = combination makes You It is on the exact same location on both chromosomes When you go to make your gametes, you can only pass down member of the pair Meiosis makes sure that the homologous pairs so this happens Meiosis is similar to Mitosis the names of the stages are the same Interphase occurs before Meiosis just like before Mitosis the chromosomes replicate Each member of the homologous pair has chromatids And different there are stages to Meiosis and the daughter cells will not be identical Stages of Meiosis I Prophase I Chromosomes condense, nuclear envelope and nucleolus break down, spindle forms Homologous Pairs find each other by undergoing and forming a - named because of the four chromatids together Non-sister chromatids may become entangled and exchange genetic material This process is called, and the place where it takes place is called a Since the genes code for the same trait, no genes are lost and the chromosome is not damaged but the sister chromatids are no longer (You do not need to know about Prometaphase in Meiosis. I have no idea why.) Metaphase I Homologous Pairs line up at the metaphase plate This process is called and also ensures that the daughter cells are not identical

4 4 Anaphase I The Homologous Pairs or separate and each moves towards a pole Note that the chromosomes still have 2 but they are no longer sister chromatids because they are no longer Telophase I This stage does not always occur, but if it does it proceeds just as Telophase of Mitosis The difference is that there are now and they are If occurs, then there may be a resting phase called: But the nuclei may not re-form, the spindle may not break down, etc Stages of Meiosis II Prophase II Chromosomes condense, nuclear envelope and nucleolus break down, spindle forms Each daughter cell has chromosomes. The cells are, but each chromosome has Metaphase II Chromosomes line up on the metaphase plate Anaphase II divide, sets of chromosomes move to the poles Telophase II Spindle fibers break down, nucleus and nucleolus reform, chromosomes relax occurs along with Telophase II, creating daughter cells Daughter cells are and genetically from the parent

5 5 The Human Life Cycle Requires both and In males, is formed via, which results in sperm cells per round of meiosis In this process, a spermatocyte with 46 chromosomes divides into a spermatocyte in Meiosis I It continues to divide into 4 spermatids with chromosomes during Meiosis II. Males produce sperm for a great deal of their lifetime while females have all of their eggs by the time they are a three month old fetus. In females, are formed via In this process, the primary divides unequally to form a larger oocyte and a smaller body. Females have unequal cytokinesis because females supply the zygote with all of the other organelles while the males only supply the nuclear formation. These other organelles help the embryo sustain itself until the is formed. The secondary oocyte goes into Meiosis II and stops at Metaphase II. If the egg is fertilized by the sperm, it is sent through the rest of, resulting in a egg and 2 more bodies. The end result is egg cell and polar bodies. The polar bodies are a way to get rid of chromosomes. Why Meiosis and Why Sex? Meiosis allows for a way to keep chromosome number constant in a species while continuing the Meiosis gives us genetic variance through and Sex allows for which increases genetic variability even more We must have variability in the genotype in order to react to variations in the environment Cancer and the Cell Cycle must be present for a cell to move on to Mitosis This is how cell growth and division is regulated Occasionally, the growth factors will not work properly and the cell is This results in uncontrolled growth and a mass of cells called a: Cancer causing genes called code for these growth factors genes create proteins that combine with certain growth factors to prevent the cancer from occurring The immune system tries to get cancerous cells to die in a process called: Cancerous tumors that are easily removed or treated are called: Cancer may spread throughout the body in a process called We call this cancer: