4Chromosome Structure 3 forms of a chromosome Chromatin – ball of yarn Chromatid – half of an x, sometimes bentChromosome – XCenter of X is called a centromere
5Chromosome Types Sex Chromosomes Autosomes Determine the sex of the organismMales XYFemales XX2 out of 46 in the human cellAutosomesAll the other chromosomes44 out of 46 in the human cell
6Sex Chromosomes and Autosomes Section 1 ChromosomesChapter 8Sex Chromosomes and AutosomesClick below to watch the Visual Concept.Visual Concept
7What are Homologous Chromosomes? Also called homologues2 copies of the chromosomeOne from Mom; One from DadHave the same sizeHave the same shapeHave the same information (genes)
8Two Types of Cells Diploid Haploid Cells that have chromosomes in pairsSymbol 2nSomatic cells or body cells are like thisHumans diploid number is 46.HaploidCells that do not have chromosomes in pairsSymbol 1nGametes are like thisSex cellsSperm and egg cellsHumans haploid number is 23.
9Cell Division in Prokaryotes, continued Section 2 Cell DivisionChapter 8Cell Division in Prokaryotes, continuedBinary fission is the process of cell division in prokaryotes.
14The process of asexual reproduction begins after a sperm fertilizes an egg.
15Three reasons why cells reproduce by asexual reproduction: 1. Growth 2 Three reasons why cells reproduce by asexual reproduction: Growth Repair ReplacementSkin cancer - the abnormal growth of skin cells - most often develops on skin exposed to the sun.Cell that reproduce by asexual reproduction reproduce constantly.
17Interphase occurs before mitosis begins 3 phasesG1 – cell is growingS – DNA is being copiedG2 – cell is preparing for mitosisNuclear MembraneAnd nucleolus are visibleCHROMATIN!CELL MEMBRANENucleusCytoplasm
19Prophase 1st step in Mitosis Nuclear membrane & nucleolus disappear by end of prophaseMitosis begins (cell begins to divide)Chromosomes are visibleCentrioles (or poles) appear and begin to move to opposite end of the cell.Spindle fibers form between the poles.CentriolesSister chromatidsSpindle fibers
25Telophase 4th step in Mitosis Nuclear membrane & nucleolus are visible by end of telophaseTwo new nuclei form.Chromosomes appear as chromatin (threads rather than rods).Mitosis ends.Overlaps with cytokinesis!NucleiNucleiChromatin
27Cytokinesis occurs after mitosis Division of the cytoplasmCell membrane moves inward to create two daughter cells – each with its own nucleus with identical chromosomes.Animal cells – form a cleavage furrowPlant cells – form a cell plate, which becomes the cell wall.
35Control of Cell Division Section 2 Cell DivisionChapter 8Control of Cell DivisionCell division in eukaryotes is controlled by many proteins.Control occurs at three main checkpoints.G1 checkpoint – check to see whether the cell is healthy and is large enough to divideG2 checkpoint – check to make sure DNA is copied correctlyMitosis checkpoint – if cell divided correctly, then signals are made to exit mitosis
36Control of the Cell Cycle Section 2 Cell DivisionChapter 8Control of the Cell CycleClick below to watch the Visual Concept.Visual Concept
37Control of Cell Division, continued Section 2 Cell DivisionChapter 8Control of Cell Division, continuedWhen Control is Lost: CancerCancer is uncontrolled growth of cellsCancer may result if cells do not respond to control mechanisms.Can be caused by mutations in DNA
38Formation of Haploid Cells Section 3 MeiosisChapter 8Formation of Haploid CellsMeiosis is a process of nuclear division that reduces the number of chromosomes in new cells to half the number in the original cell.Start with 46 and end with 23Meiosis leads to four haploid cells (gametes) rather than two diploid cells as in mitosis.Done by germ cellsMeiosis produces haploid gametes.Is considered sexual reproductionCreates genetic diversityTwo divisions
39Section 3 MeiosisChapter 8Meiosis IMeiosis I includes prophase I, metaphase I, anaphase I, and telophase I.Crossing-over, which is when portions of homologous chromosomes exchange genetics material, occurs during prophase I and results in genetic recombination.
40Prophase I Homologous chromosomes (paired chromosomes) become visible Nuclear membrane and nucleolus disappearSpindle fiber starts to appearCrossing over occurs – portions of the chromatid break off and attach to other homologous chromosome
41Tetrads and Crossing-over of Genetic Material Section 3 MeiosisChapter 8Tetrads and Crossing-over of Genetic MaterialClick below to watch the Visual Concept.Visual Concept
42Metaphase 1Homologous chromosomes (tetrads) line up at the equator and connect to spindle fibers at their centromeres
43Anaphase 1Homologous chromosomes split and individual chromosomes move to polesThey assort independently of one another- independent assortment
44Telophase 1and Cytokinesis 1 There are 2 new cells at this pointEach new cell has half the number of chromosomes as the parent germ cellSo they are now haploid
45Meiosis 2 Has prophase II, metaphase II, anaphase II and telophase II Exactly like mitosisFour new haploid cells resultFour gametesDepends on whether it is an animal or a plant cell
47Gametogenesis – making of gametes SpermatogenesisMaking of sperm cellsMeiosis will result in 4 mature sperm cells or spermatozoaOogenesisMaking of mature egg cells, or ovaMeiosis will result in 1 mature egg cell and 3 polar bodies that die