MITOSIS!  Why? –Growth and development –Repair –Asexual reproduction –All present info in the DNA must be present in each resulting cell

MITOSIS  Chromosome structure: –Coiled DNA and its associated proteins –When the DNA is copied, the exact copies of each chromosome are called Chromatids –The Chromatids are attached to each at a point called the centromere.

MITOSIS!  Chromosome Structure: –Human somatic cells (non egg and sperm) have 2 copies of 23 chromosomes for a total of 46 chromosomes. –Each of the 23 pairs consist of two homologous chromosomes. –Each came from one of two parents. –Cells that contain all 23 homologues are called Diploid –A cell that has only 1 set of homologues (sperm or egg) are said to be haploid.

MITOSIS!  Chromosome structure continued…  Diploid is represented as 2n –Example: human diploid number is 2n= 46  Haploid is represented by n –Example: human egg cell is n= 23  A zygote is a fertilized egg formed by the fusion of 2 gametes (sex cells)

MITOSIS!  Other vocab… –Autosomes: chromosomes not directly involved in the determination of gender –Sex chromosomes: one of the 23 pair of human chromosomes that aid in the determination of the sex of an individual Female sex chromosomes are XX Male sex chromosomes are XY

MITOSIS!  Mutations: changes in the chromosome structure –Deletion: a part of the chromosome breaks off completely, typically fatal –Duplication: a fragment attaches to a homologous chromosome –Inversion: a piece reattaches in reverse orientation on the same chromosome –Translocation: a piece reattaches on a different chromosome.

MITOSIS! Cell cycle  Interphase: 3 stages –A period of growth in the cell –90% of a cell’s time is spent in this stage 1.G1 phase: growth and routine cell functions 2.S phase: DNA is copied, chromatids attach at centromeres 3.G2 phase: preparation for cell division

MITOSIS Cell cycle  Prophase: 1.Chromosomes coil up and become visable 2.Nuclear envelope disappears, spindle fibers form

MITOSIS Cell cycle  Metaphase: Chromosomes move to the center of the cell, line up along equator. Spindle fibers link chromatids to opposite poles

MITOSIS Cell cycle  Anaphase: Centromeres divide and chromotids (now chromosomes again) move towards opposite poles.

MITOSIS Cell cycle  Telophase: Nuclear envelope forms around the chromosomes at each pole.  Mitosis is complete

MITOSIS Cell cycle  Cytokinesis: the cytoplasm of the cell divides

MEIOSIS…  Purpose –To form gametes (in humans, egg and sperm)  Steps: –Like mitosis in prophase, but in metaphase, the pairs of homologous chromosomes line up in the middle –This allows for 2 divisions of the genetic material so that the gametes get half of the genetic content.

Here is the process of meiosis. As you can see, it goes through 2 divisions, resulting in 4 haploid cells.