Cell Reproduction Mitosis and Meiosis Objectives Understand the

Cell Reproduction: Mitosis and Meiosis

Objectives Understand the stages of the cell cycle. Learn why cells divide.

Key Question: How do organisms grow?

Cell Cycle Cells go through certain phases called the cell cycle 5 main stages: Interphase (3 parts) Prophase Metaphase Mitosis Anaphase Telophase + Cytokinesis

Interphase The cell grows and performs its function Cells spend most of their life in interphase. Major events: Cell is growing Cell duplicates its DNA Cell prepares for mitosis

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

Mitosis is the process of somatic cell reproduction. Mitosis is asexual reproduction (diploid cells). Cells must divide to let you grow, replace dead cells, and repair your body. Mitosis is part of the cell cycle that divides the nucleus so that each new cell (daughter cell) has the same DNA as the parent cell that divided. Cells prepare for mitosis by forming chromosomes.

Dividing Cell Growing Cell Source: http: //upload. wikimedia. org/wikipedia/commons/d/d 3/Onion_root_mitosis. jpg

Prophase 1 st Stage of Mitosis Major Events: Chromosomes condense Nucleus starts to dissolve Centrioles ( animal cell) move to the sides of the cell Like anchors at the sides of the cell Spindle Long fibers appear strands… think Spider-Man

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

Metaphase 2 nd Stage of mitosis Major Events: Spindle fibers attach to centrioles and chromosomes Chromosomes are lined up in the middle of the cell

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

Anaphase 3 rd Stage of Mitosis Major Events: Spindle fibers pull the chromosomes apart toward the ends of the cell

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

Telophase & Cytokinesis 4 th and Final Phase of Mitosis Major Events: Telophase: 2 nuclei form around the groups of DNA Cytokinesis (“cell” + “movement”): Cell membrane pinches off to make two new cells These two are combined into one phase because they happen roughly at the same time.

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

Cell Cycle

Mitosis Animation Tim and Moby - Cell Division Video: Real Cells Dividing

Key Question – How Do Organisms Grow?

Key Question – How Do Organisms Grow? Mitosis! 1 cell turns into 2 new “daughter cells” This happens all the time Different types of cells have different lifespans: Skin cells – 2 or 3 weeks Nerve cells – 1 lifetime Red blood cells – 4 months White blood cells – > 1 year

Mitosis is responsible for fixing cuts and scrapes, as well as growth and development All animals start as 1 cell, which undergoes mitosis to become 2 cells, then 4, then 8, then 16, etc…until you grow to 50 – 75 trillion cells!

Video : Review Mitosis

Meiosis

Objectives State the purpose of meiosis. Compare meiosis and mitosis.

Meiosis Is a special type of cell division that occurs to produce sex cells (happens only in reproductive structures; ovaries and testes) During meiosis the cell goes through two cell divisions Meiosis 1 Meiosis 2

Meiosis 1 Five steps of Mitosis Interphase (cell cycle) Prophase Metaphase Anaphase Telophase Difference: PAIRED chromosomes separate

Meiosis 1 Interphase 1 The cell continues to grow and prepare for meiosis 1 DNA is being copied from the parent cell

Meiosis 1 Prophase 1 Chromosomes condense Nuclear membrane breaks down Chromosomes then pair up

Meiosis 1 Metaphase 1 Chromosome pairs line up Chromosomes arrange as pairs in the middle of the cell Spindle fibers attach to centromeres of each chromosome

Meiosis 1 Anaphase 1 Chromatid pairs are torn apart; they DO NOT SEPARATE. Single chromosomes move to opposite sides of the cell

Meiosis 1 Telophase 1 Cell divides No more replication of genetic material No more copies of DNA are made before it divides again. Each has ½ the normal number of chromosomes

Meiosis 2 Prophase 2 The cell prepares to divide again. Each chromosome is made up of 2 copies (sister chromatids) This is exactly like mitosis.

Meiosis 2 Metaphase 2 Chromosomes line up in the center of the cell. Spindle fibers attach to the centromeres of the individual chromosomes.

Meiosis 2 Anaphase 2 Chromosomes are ripped apart. Once chromosomes are apart they move to opposite sides of the cell.

Meiosis 2 Telophase 2 Cell membrane appears and cells divide Cytokinesis splits the cytoplasm into four new daughter cells

Meiosis-big picture Start with one cell, but end up with 4 new cells that are not identical!

Why does Meiosis happen? In organisms that reproduce sexually, ½ the DNA comes from each parent. Meiosis is the process where ½ the DNA (as chromosomes) ends up in a sex cell. The zygote then, is a combination of ½ chromosomes from each parent (50%/50%).

Chromosome Numbers These cells are sex cells or gametes. They have ½ the number of chromosomes

Comparison of Meiosis and Mitosis

Meiosis Video: Chromosome Numbers During Division - Demystified Video: Meiosis Video/Animation: Comparison of Mitosis and Meiosis