REVIEW- MITOSIS Cell Cycle Chromatin Condenses Go At Cell Maturity Chromosome now 2 sister chromatids

Chromatin, Condensed DNA, Chromosomes 95% of the time Easily Visible, 5% of the time One Chromatid

Homologous Chromosomes vs Sister Chromatids

Crossing Over Independent Assortment 23..STILL Replicated

MEIOSIS II: Separating Sister Chromatids * Do NOT COPY DNA again 23.. Single File All ‘n’

Mitosis/Meiosis Animation ml

Nondisjunction: causes errors in chromosome numbers Nondisjunction is when the chromosomes don’t split evenly in meiosis, resulting in too many or too few chromosomes in the sperm or egg. Examples of diseases/conditions caused by non-disjuction:  Down’s Syndrome = 47  Turner’s Syndrome = 45  Klinefelter’s Syndrome = Meiosis%20I.htm

Mitosis vs Meiosis

Crossing Over Prophase I First Source of Genetic Variation Chiasmata- sites of crossing over, occur in synapsis- exchange of genetic material between non-sister chromatids No longer Genetically Identical

Independent Assortment: Metaphase I 2 nd Source of Genetic Variation At least (2 23 ) 8 million possible combinations from EACH parent…. 64 TRILLION combinations for a diploid zygote Producing truly unique offspring

Third Source of Genetic Variation: Random Fertilization (which sperm will fertilize the egg?) Spermatogenesis vs Oogenesis

Spermatogenesis 2n=46 human sex cell diploid (2n) n=23 sperm haploid (n) Crossing- over occurs at this stage 4 genetically different gametes are produced

Lab Today… DVD: Visualizing Cell Process, DNA, Stages of Mitosis Onion Root Tip……Interphase and PMAT DVD: Visualizing Cell Process- DNA- Stages of Mitosis ~30sec Interphase Telephase with cell plate Metaphase Anaphase Prophase

Whitefish Blastula Mitosis Stages

Meiosis- Key Differences from Mitosis 1. Meiosis reduces the # of chromosomes by half 2. Daughter cells differ from parent and each other Mitosis- Daughter Cells are Identical (Somatic) Meiosis- At end 4 different cells….Genetic Variation 3. Meiosis involves TWO divisions; Mitosis only one.

Meiosis- Key Differences from Mitosis Mitosis Creates Body Cells; Meiosis creates Sex cells 1. Meiosis I (PMAT I) involves: Prophase: Synapsis- homologous chromosomes pair up – called a ‘tetrad’. Chiasmata form = Where Crossing Over of non-sister chromatids takes place. *First source of Genetic Variation- no longer identical. Metaphase I: Homologous pairs line up on the equator- double file- Mom with sister chromosome, dad with sister chromosome. (Double 23 across, not 46) *Independent Assortment- second source of genetic variation Anaphase I: Tetrad Splits- Sister chromatids do NOT separate at the centromere. (Pair of homologous chromatids split up)