Meiosis and Mitosis

What is a chromosome? Linear strand of packaged DNA In the nucleus of eukaryotic cells

Haploid Cells (1N) Sex cells or gametes are haploid! Reproductive Cells (gametes that contain 23 single chromosomes) Male Gamete: Sperm: produced in the testes Female Gamete: Egg: produced in the ovaries Ova-plural Ovum- singular Human Haploid # = 23

SPERM: 22 autosomal chromosomes and an X or a Y sex chromosome Haploid (1N) Sperm Cell 23 single chromosomes SPERM: 22 autosomal chromosomes and an X or a Y sex chromosome Human sex cell karyotype. A karyotype is the complete set of chromosomes of an organism. However, this karyotype comes from an oocyte (immature egg cell) and so has only the haploid (half, 23) number of chromosomes. If the egg is fertilised the chromosomes from the sperm cell will join with these chromosomes to form a whole genome of 46 chromosomes arranged in 23 pairs. or an X Sex chromosomes Autosomal chromosomes

EGG: 22 autosomal chromosomes and an X sex chromosome Haploid (1N) Egg Cell 23 single chromosomes EGG: 22 autosomal chromosomes and an X sex chromosome Sex chromosomes Autosomal chromosomes

Fertilization occurs and produces a…..

Diploid Cell with Homologous Chromosomes Homologous Pair One diploid cell with 46 homologous chromosomes (a pair of chromosomes- one from each parent) 23 total pairs = 46 chromosomes

Fertilization union of sperm and egg (gametes) Produces a diploid zygote with 46 homologous chromosomes results in sharing and exchanging of genetic information This allows for species variation in sexually producing organisms.

Fertilization Fertilization X or X 1n XY 46 homologous chromosomes in this diploid zygote Zygote = fertilized egg 23 single chromosomes 1n XY 1n X or X 23 single chromosomes

Diploid Cells (2N) Somatic (Body) Cells are diploid! Non-reproductive cells such as muscle, skin, blood contain 46 total chromosomes (23 pairs) have two homologous copies of each chromosome-one from the mother and one from the father Mom Dad Human Diploid # = 46

Karyotype- organized profile of an organism’s chromosomes within one cell Homologous Pair 22 pairs of autosomal chromosomes (44 total) This is a karyotype of a diploid body cell from a male. 1 pair of sex chromosomes (2 total)

Human Karyotype

HUMAN SEX CHROMSOMES

The sex of a person depends on whether the sperm that fertilizes the egg contains an X or a Y chromosome. 46 total 46 total

The process of mitosis begins after a sperm fertilizes an egg.

Fertilization Results In a Diploid (2n) Zygote Egg 1n Haploid nucleus Sperm 1n Haploid nucleus

Fertilization Results In a Diploid Zygote Egg 1n Haploid nucleus Sperm 1n Haploid nucleus

Fertilization Results In a Diploid Zygote Egg 1n Haploid nucleus Haploid nucleus Sperm 1n

Fertilization Results In a Diploid Zygote Egg 1n Haploid nucleus Haploid nucleus Sperm 1n

The zygote undergoes mitosis (cell division).

From Zygote to Embryo 2n 2n 2n

From Zygote to Embryo 2n 2n

From Zygote to Embryo 2n 2n 2n 2n

From Zygote to Embryo 2n 2n 2n 2n

From Zygote to Embryo All cells are diploid (2n)!

Cell Differentiation During week two of embryonic development, embryonic cells have begun the process of differentiation. The identical cells formed by the early divisions of the zygote are beginning to take on the different characteristic of muscle, blood, nerve, bone, and other kinds of cells. Different genes are turned on in different cells.

From Embryo to Fetus Fetal Stage- Week 9

To a Multicellular Human

diploid zygote with 46 chromosomes We are here right now… Now the zygote will undergo mitosis to grow into a multicellular organism XY XX diploid zygote with 46 chromosomes Multicellular Organism 23 + 23 = 46 chromosomes union of gametes Egg 23 haploid chromosomes Sperm 23 haploid chromosomes

Videos Fertilization Animation with Narration (Start at 11s) Fertilization Animation (Start at 3:23) Cell Differentiation

MITOSIS (A.K.A. Cell Division) Asexual reproduction of eukaryotic somatic (body) cells

Three reasons why body cells reproduce by asexual reproduction: 1 Three reasons why body cells reproduce by asexual reproduction: 1. Growth 2. Repair 3. Replacement

Chromosomes and Chromatids centromeres A chromosome may be a single chromatid or it may be two sister chromatids joined by a centromere. 1 Chromatid 1 Chromosome 2 Sister Chromatids 1 Chromosome

DNA replication produces sister chromatids during interphase DNA replication produces sister chromatids during interphase. This doubles the amount of genetic information in the cell and helps to ensure the two daughter cells will each contain the same number of chromosomes as the parent cell. Interphase Prophase

3 Stages to the Cell Cycle 92 46 DNA Replicates Start: 1 cell with 46 chromosomes 92 End: 2 genetically identical cells each with 46 chromosomes 46 46 92 46 46

IPMATC REMEMBER! I Procrastinate More At The Caribbean Stage 1: Interphase Stage 2: Mitosis Prophase Metaphase Anaphase Telophase Stage 3: Cytokinesis IPMATC Mi tosis A mnemonic to help remember the stages of mitosis. I Procrastinate More At The Caribbean 37

The Cell Cycle (Mitosis) in an Animal Cell

Stage1- Interphase Cell is diploid (2N)- homologous chromosomes The nucleus and nucleolus are very distinct Chromosomes appear as threadlike coils (chromatin) at the start DNA replicates - chromosome number doubles and sister chromatids begin to form Nucleolus Cell membrane Nucleus -2 Pairs of Homologous Chromosomes -4 chromatids/ 4 chromosomes Cytoplasm

Sister Chromatids two exact copies of a chromosome attached together by a centromere created during DNA replication during interphase

Interphase Plant Cell Animal Cell

Stage 2 Mitosis

Prophase - 1st step in mitosis Centrioles appear and begin to move to opposite ends of the cell (Only animal cells have centrioles! ) Spindle fibers form between the poles Chromosomes condense (become visible) Nuclear membrane starts to break down 2 Pairs of Homologous Chromosomes 8 Sister Chromatids 4 Chromosomes Centrioles Spindle Fibers

Prophase Plant Cell Animal Cell

Metaphase - 2nd step in mitosis Centrioles have reached the poles of the cell Centromeres of sister chromatids attach to the spindle fibers and line up in the middle. Nuclear membrane disappears 8 Sister Chromatids 4 Chromosomes Centromere Centrioles Spindle fibers

Metaphase Plant Cell Animal Cell

Anaphase - 3rd step in mitosis Sister chromatids separate and move to poles Ensures each daughter cell has the same number of chromosomes as the parent cell 8 Chromosomes 8 Chromatids Centrioles Spindle fibers

Anaphase Plant Cell Animal Cell

Telophase - 4th step in mitosis Animal Cells: cell membrane begins to pinch inwards to form a cleavage furrow Plant Cells: cell plate begins to form into a cell wall Both Cells: Nuclear membrane forms Two new nuclei visible Diploid chromosomes appear as chromatin Nucleus Nucleus Chromatin

Telophase Plant Cell Animal Cell

Cleavage Furrow in an Animal Cell

Stage 3. Cytokinesis Division of cytoplasm Two diploid daughter cells created – each with a nucleus and an identical number of chromosomes 2N 2N 2N 2N

Cytokinesis

Mitosis produces two identical diploid (2n) daughter cells 1-Interphase 2-Mitosis 3-Cytokinesis Two cells that are genetically identical to each other and the parent cell are formed.

Animal Mitosis - Review Interphase                                                              Prophase                                                              Metaphase                                                              Anaphase                                                              Telophase                                                              Cytokinesis                                                             

Plant Mitosis - Review Interphase Prophase Metaphase Anaphase Telophase                                                                                                                          Cytokinesis  

Cell Cycle Time Frame 2 daughter cells -It takes about 24 hours for one cell to complete the cell cycle and 80 minutes for most eukaryotic cells to undergo mitosis. 1 parent cell

What if mitosis runs rampant? CANCER- uncontrolled cell division Cancer cells do not respond to the signals that regulate cell growth. Cancer Video Cancer Video 2 Cancer is a disease of uncontrolled cell division. It starts with a single cell that loses its control mechanisms due to a genetic mutation. That cell starts dividing without limit, and eventually kills the host. Normal cells are controlled by several factors. Normal cells stay in the G1 stage of the cell cycle until they are given a specific signal to enter the S phase, in which the DNA replicates and the cell prepares for division. Cancer cells enter the S phase without waiting for a signal. Normal cells are mortal. This means that they can divide about 50 times and then they lose the ability to divide, and eventually die. This “clock” gets re-set during the formation of the gametes. Cancer cells escape this process of mortality: they are immortal and can divide endlessly. Normal cells that suffer significant chromosome damage destroy themselves due to the action of a gene called “p53”. Cancer cells either lose the p53 gene or ignore its message and fail to kill themselves.

Postmitotic (nonmitotic) Cells Do not do mitosis after reaching maturity. Include: Skeletal Muscles Heart (Cardiac Muscles) Smooth Muscle (Stomach) Neurons Brain

Mitosis Review Videos http://www.cellsalive.com/mitosis.htm Mitosis Rap Mitosis Dance 1 Mitosis Dance 2 Mitosis Animation Textbook animation Twilight Mitosis Twilight Mitosis Short Version Mitosis Cartoon- Amoeba Sisters Mitosis: Splitting up is Complicated http://www.cellsalive.com/mitosis.htm

Why must gametes have half the genetic material of body cells? Recall that the gametes each have 23 chromosomes. During fertilization the zygote inherits 23 chromosomes from the mother’s egg and 23 chromosomes from the father’s sperm. If the gametes did not have half the number of chromosomes, the chromosome number would double with each fertilization, and after a few generations, the number of chromosomes in each cell would become impossibly large!

diploid zygote with 46 chromosomes Now the zygote will undergo mitosis to grow into a multicellular organism XY XX diploid zygote with 46 chromosomes Multicellular Organism 23 + 23 = 46 chromosomes union of gametes Egg 23 haploid chromosomes Sperm 23 haploid chromosomes

So how do sex cells become haploid?

Meiosis A.K.A Reduction Division -Production of sex cells with half the number of chromosomes as a body cell. -Cell division of 1 diploid (2n) cell resulting in 4 haploid (1n) cells -Gametes are produced in the ovaries (female) and the testes (male)

1 diploid (2n) Parent cell 4 haploid (1n) daughter cells

Synapsis and Crossing Over During Prophase I of meiosis, homologous chromosomes pair up (synapsis) and exchange genetic information. This is known as crossing over. Crossing over allows gametes to receive a unique set of genetic information and produces variation of a species. Crossing Over Video

During meiosis, the chromosome pairs separate and are distributed to two different cells. The resulting sex cells have only half as many chromosomes as the other cells in the organism.

Mitosis and Meiosis Relationship

Meiosis Review Videos Meiosis Animation Meiosis Square Dance Review Video Tutorial Review! Click Here Why do ferns have more chromosomes than you? Meiosis Crash Course Meiosis 3D animation Meiosis Amoeba Sisters

Mitosis vs. Meiosis

Meiosis vs. Mitosis Review Videos ThinkWell Review The continuation of Life...a good overall review of the mitosis and meiosis relationship Meiosis and Mitosis Compare and Contrast Review Tutorial PBS How Cells Divide: Mitosis vs Meiosis Interactive Where do your genes come from? Crash Course in Meiosis

Helpful Website http://learn.genetics.utah.edu/content/chromosomes/diagnose/

So how do twins form?

Videos…Twins How do twins form? National Geographic- In the Womb (2:55)