UNIT 7: Cell Division BIG IDEA: Cell division is the process in the body to create more cells and gametes

MITOSIS

Asexual Reproduction  Reproduction with only one parent  offspring are identical to parents

Sexual Reproduction  Requires 2 parents  New individual is produced by the union of the nuclei of two specialized cells (sperm & egg)

Chromosome Structure  Inside your nucleus are 3 billion nucleotides of DNA  In order to fit it is coiled and packed into a complicated but organized structure

Chromosome Structure  Histones- Proteins that DNA are wrapped around

Chromosome Structure  Chromatin- Less tightly coiled DNA wrapped around a histone Chromatid Chromosome

Chromosomes  Rod shaped structures made up of DNA and histones  Two identical halves are called chromatids  Point holding together the chromatids is called a centromere

Chromosomes  Structure in cells that undergo division and that contain hereditary information of the organism  In mitosis the chromosomes that undergo cellular division are called autosomes

Chromosomes  Draw a chromosome and label the centromere and the chromatids centromere chromatid

How many chromosomes are present in an autosomal cell?  23 pairs or 46 chromosomes  Refers to DIPLOID: meaning that a cell possesses 2 complete sets of chromosomes

Why are there two sets of chromosomes? –1 set is from your mother and 1 set is from your father –This leads to genetic variation because genetic information on chromosomes from your parents can be different  Example: both chromosomes can code for eye color except one can be for blue eyes and one for green eyes

Blonde Hair Black Hair Genetic Variation

Why is genetic variation beneficial?  Causes a diverse collection of genes  Increase in survival

CELL CYCLE  Cycle that a cell goes through in order to make new cells  If an organism is unicelluar, than a new organism is created via the cell cycle

Cell Cycle Consists of Two Parts:  Mitosis: –Division of the nucleus to form two identical nuclei –REMEMBER: Hereditary material is found in the nucleus  Cytokinesis –Division of the cytoplasm of the cell after mitosis

INTERPHASE

Interphase  Stage when a cell is between mitotic cycles: A. G1- cell grows B. S- DNA replication C. G2- Organelle replication

MITOSIS

Prophase  Chromosome become visible  Centrioles move to opposite poles of the cells  Microtubules form spindles  Spindle fibers become attached to centromeres  Nuclear membrane disappears  Nucleolus disappears

Prophase:

Metaphase  Chromosomes attach to the microtubule spindles  Chromosomes line up on the equator of the cell

Anaphase  Centromeres double  Chromosomes(si ster chromatids) move to opposite poles  Division (cleavage furrow) appears

Telophase  Begins when chromosomes reach the poles  Chromosome uncoil and become invisible  Spindle disappears  Nuclear membrane forms  Nucleioli reappears

Telophase

Cytokinesis in Animal Cells  Begins during late anaphase  Cytoplasm is pinched off by cell membrane

Mitosis & Cytokinesis in Plant Cells  Main events are the same  Plants do not have centrioles or asters  Cytokinesis cannot occur by pinching off of membrane a cell plate forms between the new cells during anaphase or telophase

Cytokinesis End with two identical daughter cells

Cells that divide rapidly  Plants  Animals

Cells that seldom or never divide  Xylem (part of a plant)  Nerve Cells  Muscle Cells