How do little elephants grow up to be

How do little elephants grow up to be BIG elephants?

Why do animals shed their skin?

Cell Division – Mitosis

Sexual Reproduction

The process of asexual reproduction begins after a sperm fertilizes an egg.

Three reasons why cells reproduce by asexual reproduction: 1. Growth 2. Repair 3. Replacement Skin cancer - the abnormal growth of skin cells - most often develops on skin exposed to the sun. Cell that reproduce by asexual reproduction reproduce constantly.

Animated Mitosis Cycle http: //www. cellsalive. com/mitosis. htm • Interphase • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis

Cell Division: a. k. a. Mitosis - division of somatic (body) cells

Interphase Interesting things happen! Parent Cell 1. Cell preparing to divide (Resting Stage) 2. DNA replication occurs Nucleus CELL MEMBRANE Cytoplasm

Interphase Animal Cell Plant Cell Photographs from: http: //www. bioweb. uncc. edu/biol 1110/Stages. htm

Prophase • • • Chromosome pair up! Chromosomes thicken and shorten - become visible Chromatin Chromatid Chromosomes: Joined together by a centromere Centrioles (or poles) appear and begin to move to opposite end of the cell Spindle fibers form between the poles Nuclear membrane disintegrates Sister chromatids Centrioles Spindle fibers

Prophase Animal Cell Plant Cell Spindle fibers Centrioles Photographs from: http: //www. bioweb. uncc. edu/biol 1110/Stages. htm

Chromosomes • A chromosome (KROH muh sohm) is a structure in the nucleus that contains hereditary material.

Metaphase Chromosomes meet in the middle ! 1. Twin chromosomes arrange at equator of cell 2. Become attached to spindle fibers by centromeres Centrioles Spindle fibers

Metaphase Animal Cell Plant Cell Photographs from: http: //www. bioweb. uncc. edu/biol 1110/Stages. htm

Anaphase • • Chromosomes get pulled apart Chromosomes separate and begin to move to opposite ends of the cell Centrioles Spindle fibers

Anaphase Animal Cell Plant Cell Photographs from: http: //www. bioweb. uncc. edu/biol 1110/Stages. htm

Telophase Now there are two! • Cytoplasm starts to pinch in • Two new nuclei form • Nuclear membrane reappears • Nuclei

Telophase Animal Cell Plant Cell Photographs from: http: //www. bioweb. uncc. edu/biol 1110/Stages. htm

Cytokinesis occurs after mitosis • Cell membrane moves inward to create two daughter cells – each with its own nucleus with identical chromosomes

Animal Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Cytokinesis / Interphase

Plant Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Cytokinesis / Interphase

Meiosis -production of gametes (sex cells) Cell division – reduction division 4 daughter cells produced Each daughter cell has half the chromosomes of the parent 2 sets of cell division involved

Why do we need meiosis? Meiosis is necessary to halve the number of chromosomes going into the sex cells At fertilization the male and female sex cells will provide ½ of the chromosomes each – so the offspring has genes from both parents

Meiosis – mouse testes

Meiosis – division error

Trisomy 21 – Downs Syndrome