Transcript Meiosis Notes
Chapter 10 Section 2 NotesMeiosis • Gene--A segment of DNA that controls production of a protein, exists on a chromosome • A chromosome--can contain a thousand or more genes along its length Chromosome • In most animals and plants--chromosomes occur in pairs • Humans--have 23 pairs or 46 total chromosomes •Homologous chromosomes--The 2 chromosomes of a pair • Diploid--A cell in which the chromosomes occur in pairs (2n) •Human body cells--are diploid and have a pair of each chromosome • Haploid--A cell that contains only one chromosome from each pair (n) •Gametes--haploid sex cells. •male=sperm female=egg Diploid and haploid cells Chromosome Numbers of Common Organisms Organism Body Cell (2n) Gamete (n) 4 Fruit fly 8 Garden pea 14 7 10 Corn 20 12 Tomato 24 Leopard Frog 26 13 Apple 34 17 Human 46 23 Chimpanzee 24 48 Dog 78 39 Adder’s tongue fern 1260 630 • This table shows the diploid and haploid number of chromosomes of some species. • Fertilization--fusion of male and female gametes to form zygote •Zygote--diploid cell (2 of each chromosome) •Sexual reproduction--production and combination of gametes • Meiosis--Cell division that produces gametes that have 1/2 the number of chromosomes as the parent cell (haploid) •Meiosis has--2 separate cell divisions, meiosis I and meiosis II Haploid gametes Sperm Cell (n=23) Meiosis Egg Cell Fertilization Diploid zygote (2n=46) Mitosis and Development Multicellular diploid adults (2n=46) • Meiosis begins with 1 diploid cell and ends with 4 haploid cells or gametes • Each gamete has half the number of chromosomes as a diploid cell Meiosis II 1 diploid cell with 4 chromosomes 4 haploid cells with 2 chromosomes each Meiosis I •Prophase I •DNA coils into tetrads •Spindle forms •Crossing over--DNA is swapped between chromosomes in a pair Meiosis I •Metaphase I •Tetrads (2 pairs of homologous chromosomes) line up along the equator of the cell Meiosis I •Anaphase I •Tetrads are separated into chromosome pairs and move to opposite ends of the cell Meiosis I •Telophase I •Spindle disappears •Chromosomes uncoil •Cytoplasm divides into 2 cells Meiosis II • Meiosis II--has 4 stages, prophase II, metaphase II, anaphase II, and telophase II •Each stage--occurs just like the stages of mitosis Prophase II Metaphase II Anaphase II Telophase II Meiosis II Prophase II: A spindle forms in each of the 2 new cells Spindle fibers attach to the chromosomes Nuclear envelope disappear Metaphase II The sister chromatids line up in the middle of the cell at the equator. Meiosis II Anaphase II: Centromere of the chromosomes split, allowing the sister chromatids to separate The chromatids begin to move to the opposite ends of the cell Meiosis II Telophase II: Sister chromatids reach opposite ends of the cell Spindles disappear and the nuclear envelope appears Cytoplasm divides MEIOSIS Comparison of Mitosis and Meiosis Mitosis Occurs in most body cells One division Meiosis Occurs only in sex cells Two divisions One cell makes 2 diploid One cell makes 4 cells haploid cells Identical to the parent Different from parent The Phases of Meiosis Click image to view movie.