The Cell Cycle and Meiosis

Cell cycle-process by which somatic cells make more of themselves ( reproduce) Makes exact copies, called daughter cells 3 parts: Interphase-G1( rapid growth, occupies most of the life of a cell), S( DNA is copied), G2( Final growth) Mitosis- prophase (4), metaphase( 2), anaphase(1), telophase ( 3) THE DIVISION OF THE NUCLEUS!!!!!!! Cytokinesis- division of the cytoplasm and the organelles 3 checkpoints-G1,G2,metaphase

 Vocabulary to know:  Chromatin-DNA in a “beads on a string” form during interphase  Chromosome- a visible form of DNA  Chromatid- half of a chromosome  Histone-a protein used to allow DNA to wrap around it so it doesn’t get kinked up, kinda like on a yoyo  Centromere- a region on a chromosome that holds the sister chromatids together  Centriole-an organelle that helps to form the spindle fibers  Prokaryote, Eukaryote, Parts of the Cell Theory ( old stuff you best know!!!)

 The DNA(genetic material) in a eukaryotic cell during interphase is in a form called chromatin. Looks like “beads on a string” that wraps around itself. This allows it to fit inside the nuclear membrane  The DNA in a bacterium(singular) or bacteria( plural) is in a circular form, like twisting a rubber band on itself many times  Normal cells become cancer cells when they do not respond to the checkpoints

Meiosis “Lingo”  Vocabulary to know:  Gamete- a reproductive cell  Zygote- when two different gametes fuse together during fertilization  Sperm- a male gamete  Ovum- a female gamete  Homologous chromosome-chromosomes that are similar in size, shape and kinds of genes they contain. Each chromosome in a homologous pair comes from one of the two parents.  Crossing over- when chromatids exchange genetic material during PROPHASE I  Independent assortment-the random distribution of homologous chromosomes during meiosis

 Vocabulary cont:  Haploid- a cell that has 1 set of chromosomes (n), 23  Diploid- a cell that has 2 sets of chromosomes ( 2n), 46  Autosome- chromosomes that DO NOT determine the sex of an individual. In a human, these are chromosome pairs 1 thru 22  Sex Chromosome- chromosomes that determine the sex of an individual. In a human these make-up the 23 rd pair  Gene- a specific area on a chromosome that codes for a trait  Trait- a genetically determined characteristic ( ex: green eyes, black hair, etc..

Types of Asexual Reproduction  Budding- part of the parent organism pinches off and forms a new organism. Ex; yeast  Fragmentation- Ex: the fungus that causes athletes foot  Binary fission- occurs in single cell organisms ( a bacteria) in which one cell divides into two cells of the same size  Vegetative reproduction- occurs in plants. New palnts grow from non- reproductive parts like the stem, root, leaves. Ex: potatoes, strawberries

Sexual Reproduction  Only one type, FERTILIZATION !  2 parents give genetic material to produce offspring that are genetically different than their parents. Requires gametes, an egg and a sperm.  These gametes are produced from germ cells. These are cells specialized for sexual reproduction.  All of the other cells in the body are called somatic cells.  This process occurs in MOST eukaryotic organisms

Comaparing Sexual vs. Asexual Reproduction  Asexual  Advantages:  Simplest, most primitive  Most efficient  Allows for many offspring in a short amount of time  Requires little energy  Disadvantages:  Little to no genetic variation in the offspring compared to the parents, therefore they may be vulnerable to changes in the environment

 Sexual Reporoduction  Advantages:  Produces genetically diverse individuals, therefore there will likely be offspring that could survive a major environmental change.  Disadvantages:  Requires 2 individuals ( may be difficult to find a mate)  Requires a lot of energy ( fighting for a mate, traveling long distances,requires specialized parts, etc)  Requires specialized cells  Process is kinda complicated ( ex: all the steps of meiosis)

Human Chromosome Make-up  Human GAMETES have 22 autosomes ( non sex determining) and 1 sex chromosome, this makes up the haploid number (n) of 23  The human ZYGOTE has 44 autosomes and 2 sex chromosomes  The sex chromosomes are labeled X and Y  Males have the chromosome make-up of XY, females are XX  Because males have 2 different forms, they determine the sex of the child. The female can only give an X but the male can give an X or a Y

Meiosis In Action  The process of taking a DIPLOID cell thru 2 divisions to form 4 HAPLOID cells  Goes thru cell division TWICE !  Steps:  Interphase  Prophase I  Metaphase I  Anaphase I  Telophase I  Prophase II  Metaphase II  Anaphase II  Telophase II  Cytokinesis

Differences between Mitosis and Meiosis  Mitosis  produces 2 genetically identical daughter cells that are diploid  Only occurs in somatic cells ( for growth, repair, and ASEXUAL reproduction)  Only has 1 cell division  Begins with chromosomes  Meiosis  Produces 4, NON-IDENTICAL daughter cells that are haploid  Only occurs in reproductive cells and is used for SEXUAL reproduction  Goes thru 2 cell divisions  Begins with HOMOLOGOUS CHROMOSOMES. In Prophase I, every chromosome pairs with its homologue ( an identical chromosome: XX). Now called a tetrad. Parts of these homologues exchange pieces of their chromatids with each other in a process called CROSSING OVER.  When the homologous chromosomes line up in Metaphase I, they do so randomly, this is called INDEPENDENT ASSORTMENT.

Summary  Mitosis produces 2 identical diploid cells in somatic cells. Efficient, very simple, little energy required. Mostly occurs in single-celled organisms( prokaryotes). No ( or very little) genetic variation. Only requires one organism. For repair, growth/development and asexual reproduction.  Meiosis produces 4 non-identical haploid cells. Only with reproductive (germ) cells. Occurs in most eukaryotic cells. For creating cells for sexual reproduction. LOTS of genetic variation!!!!! 3 main things that lead to this variation:  Crossing-over  Independent assortment ( each of the 23 pairs of chromosomes separate independently, thus 2 23 gametes( 8 million) with different gene combo’s can be made from one original cell  Random fertilization ( to show how much variation, in humans the possibility is 2 23 x ( 64 trillion ) different combinations !!!!!!!!!