Cell division

• Binary fission


  Dividing in half
• Mitosis


  Cell division that produces genetically identical daughter cells
• Meiosis


  Cell division that produces genetically distinct daughter cells
• One of the characteristics of life is that organisms reproduce their own kind
• The simple "facts of life" have been recognized for thousands of years
• Organisms that only produce their own kind

  • Paramecium
  • Archaebacteria
  • Mushrooms
  • Roses
  • Dogs
  • Elephants
  • People
• Reproduction


  The creation of genetically identical offspring by a single parent, without the participation of sperm and egg
• Cell division


  When one cell undergoes reproduction, the two daughter cells that result are genetically identical to each other and the original parent cell
• Chromosome duplication


  1. Before the parent cell splits into two, it duplicates its chromosomes

  2. One set of chromosomes is distributed to each daughter cell
• The result of cell division is a genetically-identical set of offspring
• Eukaryotic chromosome


  • More than 50% protein
  • Many of these proteins are concerned with DNA and RNA synthesis
• Single celled organisms reproduce by dividing in half
• Asexual reproduction


  The creation of genetically identical offspring by a single parent, without the participation of sperm and egg
• Asexual reproduction in multi-cellular organisms


  • Sea star species can grow new individuals from fragmented pieces
  • House plant clipping
• In all asexual reproduction, the lone parent and each of the offspring have identical genes
• Asexual reproduction via budding

  • Hydra
• Prokaryotic chromosome


  Most genes are carried on a singular DNA molecule
• The chromosome of the bacterium Escherichia coli is about 500 times longer than the cell itself
• Binary fission in a prokaryote

  1. Chromosome duplication

  2. Copies move to opposite ends

  3. Cell elongates

  4. Cell divides into two daughter cells
• Sexual reproduction requires fertilization of an egg by sperm
• Gametes


  Egg and sperm
• Fertilization of an egg by sperm

  Results in offspring not identical to parents, contributing to genetic diversity
• In sexually reproducing species, like does not beget like
• Sexual reproduction

  Offspring resemble their parents more than unrelated members of the same species, but are not genetically identical to their parents or to each other
• Every offspring inherits a unique combination of genes from its two parents, programming a unique set of traits
• Monozygotic (identical) twins


  Form from a single fertilized egg that splits into two parts after conception
• Dizygotic (fraternal) twins

  Result from the fertilization of two separate eggs with two different sperm during the same pregnancy
• Mitosis

  The essential biological process which ensures the uniform transmission of genetic material from one generation to another
• Meiosis


  The essential biological process which ensures the uniform transmission of genetic material from one generation to another
• Almost all of the genes in the cells of humans, and all eukaryotes, are found in the cell nucleus and grouped into multiple chromosomes
• Chromatin


  The loose state of chromosomes as long thin fibers, composed of roughly equal amounts of DNA and protein molecules
• Chromosome compaction before cell division

  Chromatin coils up to form tight, distinct chromosomes visible under a light microscope
• Cell cycle


  The repeating pattern of cell division, growth, and differentiation
• In the human body, millions of cells must divide every second to maintain the total number of about 10 trillion cells
• The rate of cell division varies, with some cells dividing once a day, others less often, and some highly specialized cells not dividing at all
• Differentiated cells


  Cells that have become specialized for specific functions
• Categories of cells based on division and differentiation

  • Stem cells
  • Differentiated cells capable of division
  • Permanently differentiated cells
• Stem cells


  • Self-renewal: retain capacity to divide
  • Potency: dividing stem cells produce daughter cells that can differentiate into a variety of specialized cell types
• Plants also have stem cells, usually called meristem cells, in the growing tips of roots, stems, and branches
• Differentiated cells capable of dividing

  Daughter cells typically differentiate into only one or two cell types