MITOSIS AND MEIOSIS STUDY GUIDE CREATED BY : Alistaire Rauch (Mr. Galego s Class) Definition of Mitosis and Meiosis (Basic): Mitosis and Meiosis are basically cycles of cells but they are different in many ways, so let s begin the simple definitions of what each is, meiosis is the process of when one cell divides into four different cells with half the genetic information. The types of cells within the human body that do this would be the sperm cells in the males and in the females it would be the egg cells. On the other hand mitosis is the process where a single cell divides into two daughter cells with the same amount of genetic information. Each cell has chromosomes which basically hold the DNA within each cell, therefore it is practically the genetic information. Meiosis vs. Mitosis: Now some major differences between meiosis and mitosis is that meiosis has two main different phases being Meiosis I and Meiosis II, but either process (meiosis and mitosis) both include interphase, prophase, metaphase, anaphase, and telophase. Each stage is slightly
different depending on the type of cells that either use meiosis or mitosis. Meiosis is a sexual reproduction, which occurs in humans, animals, plants, and fungi while mitosis is a type of asexual reproduction which occurs in all different types of organism. Another difference is that in meiosis there is 4 haploid cells produced while in mitosis there is 2 diploid cells, haploid basically means that it is half the chromosomes instead of a full set while diploid means that it has a full pair of chromosomes; all of this means that the in meiosis the chromosome number is reduced by half from when the parent cell produces its daughter cells, while in mitosis it always remains the same amount. In meiosis it means that there will be diversity in the offspring while mitosis is meant to easily grow and repair the body without any genetic changes. Chromosome (Anatomy): Chromosome the word itself comes from the Greek word for color, chroma and body soma. A chromosome is made of one single molecule of deoxyribonucleic acid, also known as DNA (Adenine, Thymine, Cytosine, Guanine (DNA structure)), basically it is a unique structure which allows the DNA to be tightly wrapped together in something called histones (spool-like proteins), this structure is very important in DNA replication because it makes it so they can be copied very accurately. Another purpose is that without this structure, than the number of chromosomes can be changed, and this very bad because it can lead to serious problems, such as down syndrome which we will talk about later on. A chromosome is made up of the following, two chromatids normally, a chromatid is basically the two thread-like strands which divide during cell division, and each one of these chromatids consist of DNA. On the end of each chromatid is something called a telomere which is what one might consider to be the caps on the end of shoelaces, the telomere keeps the strand of DNA from unraveling. In the middle of a chromosome is the centromere which is the point of which the two chromosomes are connected, in the X shape, the middle. Phases of Meiosis: The main phases of meiosis are:
MEIOSIS I MEIOSIS II Meiosis I : Interphase Prophase I Metaphase I Anaphase I Telophase & Cytokinesis Meiosis II : Prophase Metaphase II Anaphase II Telophase & Cytokinesis Meiosis I: 1. Interphase : - In this phase the DNA is replicated or copied which results in two full sets of chromosomes, both of which are identical 2. Prophase I: - In this phase the chromosomes change into X forms (with two chromatids) where they are identical still, also each chromosome pairs up with the same one (chromosome one with chromosome one etc.) - During this stage, small bits of chromosomes or DNA are exchanged between them - Meiotic Spindle extends between the centrioles which are organelles located close to the nucleus and they produce spindles needed for cell division (each are located along the poles now) 3. Metaphase I: - The chromosomes line up along the equator of the cell - The meiotic spindle attaches to each one chromosome of the pairs (each are located on the opposite poles now) 4. Anaphase I: - The chromosomes are now pulled apart by the meiotic spindles where they are pulled to each pole
- The sister chromatids that were created stick together and this is what is different from mitosis and meiosis II 5. Telophase + Cytokinesis: - In telophase, each chromosome moves to the opposite poles where the full set of chromosomes begins to gather together - Membranes form around the chromosomes to create two new nuclei - The single cell then splits in the middle and becomes a daughter cell which each contain a full set of chromosomes (cytokinesis) Meiosis II: (LINKED TO MEIOSIS I (continued from it) 6. Prophase II: - The two daughter cells come together to form another X shape chromosome, each membrane of the daughter cell dissolves - Meiotic spindle is created again 7. Metaphase II: - The cells line up along the equator end-to-end - Meiotic spindle attaches 8. Anaphase II: - Meiotic spindle pulls them to poles of where upon they are separated and become individual chromosomes 9. Telophase II & Cytokinesis: - Chromosomes move to opposite poles, and gather together, where new membrane forms around them to create new nucleus - 2 rounds of cytokinesis (aka splitting of cytoplasm) Phases of Mitosis: The main phases are: Mitosis : Interphase Prophase Metaphase Anaphase Telophase
Mitosis: 1. Interphase: - DNA is copied for cell division 2. Prophase: - Chromosomes condense into an X shape (pair up according) - Membrane surround nucleus dissolves - Mitotic spindle extends 3. Metaphase: - Chromosomes line up on equator - Spindle attaches to chromatids 4. Anaphase: - Chromatids are pulled apart by spindle and they are pulled to opposite poles 5. Telophase: - Chromosomes gather together to create new nuclei - Single cell punches in the middle two form two new cells containing full set of chromosomes (cytokinesis) The Cell Cycle: In the cell cycle it begins with interphase which is basically the preparation stage before the cell can enter cell division, this stage is where the cell takes in nutrients. This stage also accounts for about 90% of its life; within this stage it consists of G 1, S, and G2. During G 1 or growing stage, the cell resumes its high rate of activities from M phase; the organelles all grow aka mitochondria etc.. During S phase, this is when the DNA replication or copying begins, and this stage itself is quickly completed because the base pairs are exposed to harmful factors. In phase G 2
this is when the cell wall will continue to grow in order for everything to be ready for mitosis or meiosis. After this Mitosis or Meiosis phases occur. Binary Fission: Binary fission is when two cells divide, this is mostly for prokaryotic cells; this process might seem quite simple but the cell must know when to divide at the right time, right place, and it must be capable of supplying each offspring with a complete copy. This process begins with the FTsZ ring where upon it splits the cytoplasm in the cell, and the ring is placed in such away so that it doesn t damage any of the DNA. Differences between Meiosis and Mitosis Summed up: (chart provided by Mr.Galego)
Chromosome Abnormalities: These may happen on account to the fact that in meiosis if it does not occur properly it could lead to a baby having one more or one less chromosome (extra = trisomy; missing chromosome = monosomy). In mitosis it is the same thing, babies are created from one cell, and if it messes up the entire body will have the same problem. An example of this is down syndrome which is when there is a trisomy or extra chromosome where the body has three copies of genes instead of two. This is caused by nondisjunction or when the chromosomes fail to separate during fertilization. NOTES: - Meiosis II is very similar to Mitosis due to the fact that sister chromosomes are divided or split during Anaphase II - Meiosis results in haploid cells (half of DNA or chromosome count from parent cell) while Mitosis results in full amount of chromosomes or diploid cells - Something special to meiosis is that they line up in pairs (up-down)
Realistic Phases (EXTRA): Yes I took photo through microscope, it's of an onion