ALL CELL DIVISION STARTS WITH INTERPHASE

INTERPHASE is part of the cell cycle that occurs between divisions.   -During this phase the cell is producing materials necessary for cell division. -3 Phases G1- growth and development S - (Synthesis) chromosomes replicate (copy) G2- synthesis of organelles for cell division EX. centrioles.

What is Happening with the DNA? 1. DNA is generally found in the CHROMATIN form which is thin and fibrous during interphase. 2. Chromatin condenses to form sister chromatids which are identical structures of replicated chromosomes joined at the centromere. centromere - point where sister chromatids are joined together. This point varies depending on the chromosome.

SISTER CHROMATID Chromosome 1 is an exact copy of Chromosome 2 Chromosome 1 Chromosome 2

MITOSIS-Process during which the cell nucleus divides into 2 identical nuclei   -4 Stages I - Prophase II - Metaphase    III - Anaphase  IV - Telophase

1. Prophase Chromosomes in the nucleus condense to form sister chromatids. Centrioles move to opposite sides of the cell. B. Spindle Fibers (small tubules made up of proteins) start to form from each centriole. Nuclear Membrane breaks into fragments. Spindle Fibers attach to the centromeres. D. Nuclear Membrane disappears. Spindle fibers begin to move the sister chromatids towards the center of the cell.

2. Metaphase Spindle fibers pull sister chromatids to line up in the center of the cell. This imaginary line is called the metaphase plate. If this does not happen correctly, genetic material will not be evenly distributed.

3. Anaphase Centromeres break up. B. Spindle fibers pull 1 set of chromatids (1 sister- 1 set of chromosomes) towards 1 pole and 1 set towards the other pole.

4. Telophase – Reverse of Prophase Nuclear Membranes begin to form. B. Spindle fibers disassemble. C. Chromosomes uncoil to form chromatin. D. 2 complete nuclear membranes are finished.

Name each stage as you see it occur? Mitosis Animation

Cytokenesis -cell division (cytoplasm divides) In animal cells- cell membrane pinches off. In plant cells – pieces of membrane form at the metaphase plate & grow together to forma new cell membrane. A cell wall forms between the membranes.   Mitosis occurs in ALL of our cells. ALL of our cells have copies of ALL of our DNA.  Each cell produced by mitosis is diploid.

Cytokinesis Cleavage furrow in animal cell Cell plate in plant cell

It’s all about the number of Chromosomes.   Diploid – Contains 2 complete sets of chromosomes (2n). In humans 1 set from mom, 1set from dad so a total of 46 chromosome Ex. Chromosomes containing genes for blond AND black hair color. (Don’t forget chromosomes double right before cell division so you are looking at 92 chromosomes at the start of mitosis and meiosis for humans) Mitosis produces new somatic (body cells) and Asexual reproduction.

Cut out and put in order labeling which phase

Name the Stages of Mitosis: Early prophase Early Anaphase Metaphase Interphase Early Telophase, Begin cytokinesis Late Prophase Late telophase, Advanced cytokinesis Mid-Prophase Late Anaphase

Identify the Stages ? ? ? ? ? ? ? Early, Middle, & Late Prophase Metaphase Anaphase Late Prophase ? ? ? Telophase & Cytokinesis Late Anaphase Telophase

Meiosis occurs to produce gametes in SEXUAL reproduction.   Gametes – sex cells, haploid reproductive cells. In humans the sperm and the egg. Haploid – Contains only 1 set of chromosomes (1n). In humans only gametes contain a total of 23 chromosomes. Ex. Chromosomes containing genes are for either blond OR black.

Meiosis –cell reproduction by division which reduces the number of chromosomes in half- In humans 4623. (pg 276-277)   1 cell divides to form 4 cells with half the number of chromosomes. (Don’t forget chromosomes double right before cell division so you are looking at 92 chromosomes at the start of meiosis for humans)

Why do I want ½ number of chromosomes in sex cells? from mom from dad child too much! meiosis reduces genetic content The right number!

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How Homologous chromosomes Lining Up in Metaphase 1 is 1 Key to Variation. Gene X Hair color Sister Chromatids (same genes, same alleles) Homologous same genes, different alleles (choice Of genes blond hair/black Hair) Homologs separate in meiosis I and therefore different alleles separate.

Crossing-Over 1. Homologous chromosomes in a tetrad cross over each other 2. Pieces of chromosomes or genes are exchanged 3.Produces Genetic recombination in the offspring

Meiosis Animation

Fertilization- Gametes fuse to form a zygote-the first cell of a new organism.

Zygote- 1st cell after fertilization.