Processes involved in cell replication and DNA

• what is mitosis ?

  a method of asexual reproduction in which promotes growth and replaces worn out cells. It occurs in Somatic cells. Makes an exact copy of itself (NO genetic variation) Starts with diploid (2n) cell and ends with two diploid (2n) daughter cells.
• what is meiosis?

  
  

  a method of sexual reproduction. The first phase creates two genetically new haploid cells. Only genetically new (from cross over) homologous chromosomes are separated in Anaphase I. the second phase creates four genetically new haploid cells, each with a single set of chromosomes. Sister chromatids are separated in Anaphase II.
• Mitosis interphase?

  
  

  each chromosome becomes replicated. A cell that starts with four chromosomes would end up with four pairs of chromosomes at this stage. One with 46 chromosomes would end up with 92
• Mitosis prophase?

  
  

  
  

  DNA will supercoil and form the ‘x’ shape chromosomes, Nucleus membrane degenerates, Chromosomes become shorter and thicker. Each chromosome and its replica are held together by a structure called the centromere.The centromere (parts of a chromosome where the two chromatids join) go to poles and spindles start to form. This stage ends with the breakdown of the nuclear membrane
• MITOSIS METAPHASE

  Centrosomes extend spindles and attach these to centromere Chromosomes, thus, line up at the equator of the cell.
• MITOSIS ANAPHASE

  Spindles will contract, and they will pull apart the chromosomes Sister chromatids (half of a chromosome) go to opposite poles of the cell.
• MITOSIS TELOPHASE

  The chromosomes uncoil to become slender threads. A new cell membrane forms at the equator. The cytoplasm divides and two new daughter cells now exist, Each daughter cell ends up with four chromosomes which are identical to the original four present in the parent cell. Cleavage → starting to break into 2 cells.
• MITOSIS CYTOKINESIS

  2 identical daughter cells form
• MEIOSIS INTERPHASE

  The DNA in the cell is copied resulting in two identical full sets of chromosomes.
• MEIOSIS PROPHASE 1

  DNA condenses into chromosomes Homologous chromosomes pair up. At the END of PROPHASE I, CROSSING OVER can occur – paired homologous chromosomes may exchange sections of chromosomes at a locus. 
• MEIOSIS METAPHASE 1

  Parent cell's nuclear membrane breaks down. Chromosomes move to the equator/center  of the cell AND Spindles form
• MEIOSIS ANAPHASE 1

  Network of spindle fibers RANDOMLY separate the chromosomes to opposite ends of the cell.
• MEIOSIS TELOPHASE 1

  Nuclear membranes form around the separated chromosomes.
• MEIOSIS CYTOKINESIS 1

  Cell membrane pinches off to make two daughter cells.
• MEIOSIS PROPHASE 2

  Nuclear membranes break down.
• MEIOSIS METAPHASE 2

  Chromosomes align at the center of the cell.
• MEIOSIS ANAPHASE 2

  Network of spindle fibers separate SISTER CHROMATIDS.  Separated chromatids move to opposite ends of the cell
• MEIOSIS TELOPHASE 2

   Nuclear membranes form around separated chromatids.
• MEIOSIS CYTOKINESIS 2

  Membranes pinch off to make FOUR different haploid daughter cells (gametes)
• DNA stands for deoxyribonucleic acid which is a complex chemical found in the nucleus of te cell
• DNA is made up of 2 long strands of DNA arranged in a spiral (double helix structure) 

  • Made from 4 base pairs, made form the DNA bases adenine, guanine, thymine, cytosine (A pairs with- T &  G pairs with C)
• Genes are small sections of DNA that are the genetic code for an inherited characteristic. You inherit one gene pair (one allele) from each parent
• Genes are arranged into larger coiled structures (chromosomes). Humans have 46 chromosomes in total. We inherit 23 from each of our parents.
• DNA makes up genes, genes make up chromosomes, chromosomes make up the genome
• Homologous chromosomes are a pair of chromosomes that are similar and shape and size. this shape and size needs to pair up (cannot be small and big chromosome
• A tetrad is a pair of homologous chromosomes or 4 (tet) sister chromatids