!!GENETICS!! --- Part 5

Cell Division --- Mitosis and Meiosis 

Mitosis is the process by which a cell has previously replicated each of its chromosomes. Separates the chromosomes in its cell nucleus into two identical sets of chromosomes, each set in its own new nucleus. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles, and cell membrane into two cells containing roughly equal shares of these cellular components. 

• Mitosis and cytokinesis together define the mitotic (M) phase of the cell cycle—the division of the mother cell into two daughter cells, genetically identical to each other and to their parent cell. 
• Mitosis occurs only in eukaryotic cells and the process varies in different species.
• Prokaryotic cells, which lack a nucleus, divide by a process called binary fission.
• The sequence of events is divided into stages corresponding to the completion of one set of activities and the start of the next. These stages are prophase, prometaphase, metaphase, anaphase and telophase. 
  
  
   

Meiosis is a special type of cell division necessary for sexual reproduction in eukaryotes. 

• The cells produced by meiosis are either gametes (the usual case in animals) or otherwise usually spores from which gametes are ultimately produced (the case in land plants). 
• In many organisms, including all animals and land plants, gametes are called sperm in males and egg cells or ova in females.
• Meiotic division occurs in two stages, meiosis I and meiosis II, dividing the cells once at each stage. The first stage begins with a diploid cell that has two copies of each type of chromosome, one from each the mother and father, called homologous chromosomes. All homologous chromosomes pair up and may exchange genetic material with each other in a process called crossing over. 
• In the second stage, each chromosome splits into two, with each half, called a sister chromatid, being separated into two new cells, which are still haploid. This occurs in both of the haploid cells formed in meiosis I. Therefore from each original cell, four genetically distinct haploid cells are produced. These cells can mature into gametes.