6 When a cell divides, chromatin fibers are very highly folded, and become visible in the light microscope as chromosomes.During interphase (between divisions), chromatin is more extended, a form used for expression genetic information.
7 DNA is organized into informational units called genes Chromosomes contain hundreds to thousands of genes
8 Cell Cycle The cell cycle is a sequence of cell growth and division. The cell cycle is the period from the beginning of one division to the beginning of the next.The time it takes to complete one cell cycle is the generation time.
9 Cells divide when they reach a certain size NO (nerve, skeletal muscle and red blood cells)Cell division involves mitosis and cytokinesis.Mitosis involves division of the chromosomes.Cytokinesis involves division of the cytoplasm.Mitosis without cytokinesis results in multinucleate cells.
10 Eukaryotic cell cycle Beginning of one division to beginning of next Stages in eukaryotic cell cycleInterphaseFirst gap phaseSynthesis phaseSecond gap phaseM phaseMitosisCytokinesis
12 Chromosomes become duplicated during interphase Cells are very active during interphase, synthesizing biological molecules and growing the G1 (gap) phaseThe S (synthesis) phase is marked by DNA replicationThe G2 (gap) phase occurs between the S phase and mitosis
13 Despite differences between prokaryotes and eukaryotes, there are several common features in their cell division processes.Replication of the DNA must occur.Segregation of the "original" and its "replica" follow.Cytokinesis ends the cell division process.Whether the cell was eukaryotic or prokaryotic, these basic events must occur.
14 Hereditary material is passed on to new cells by mitosis or meiosis Cell division, growth, and reproductionInterphaseMitosisCytokinesisMeiosis
15 Cell divisionChromosomal packaging of DNA allows efficient distribution of genetic material during cell divisionLife cycle requires two distinct types of cell division processes: mitosis and meiosisCell division: one cell becomes two cells during an organism’s life cycle
16 MitosisMitosis is nuclear division plus cytokinesis, and produces two identical daughter cells during the following steps:ProphaseMetaphaseAnaphaseTelophase.Interphase is often included in discussions of mitosis, but interphase is technically not part of mitosis, but rather encompasses stages G1, S, and G2 of the cell cycle.
18 Interphase The cell is engaged in metabolic activity and performing its prepare for mitosis (the next four phases that lead up to and include nuclear division). Chromosomes are not clearly discerned in the nucleus, although a dark spot called the nucleolus may be visible. The cell may contain a pair of centrioles (or microtubule organizing centers in plants) both of which are organizational sites for microtubules.
19 Prophase Chromatin in the nucleus begins to condense and becomes visible in the light microscope as chromosomes.The nucleolus disappears.Centrioles begin moving to opposite ends of the cell and fibers extend from the centromeres.Some fibers cross the cell to form the mitotic spindle.
20 Prometaphase The nuclear membrane dissolves, marking the beginning of prometaphase.Proteins attach to the centromeres creating the kinetochores.Microtubules attach at the kinetochores and the chromosomes begin moving.
21 Spindle fibers line the chromosomes along the middle of the cell nucleus. This line is referred to as the metaphase plate.Polar microtubules extend from the pole to the equator, and typically overlapKinetochore microtubules extend from the pole to the kinetochoresThis organization helps to ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome.Metaphase
22 Anaphase The paired chromosomes separate at the kinetochores and move to opposite sides of the cell.The chromosomes are pulled by the kinetochore microtubules to the poles and form a "V" shapeMotion results from a combination of kinetochore movement along the spindle microtubules and through the physical interaction of polar microtubules.
23 Telophase Chromatids arrive at opposite poles of cell, and new membranes form around the daughter nuclei.The chromosomes disperse and are no longer visible under the light microscope.The spindle fibers disperse, and cytokinesis will start.
24 Cytokinesis In animal cells, cytokinesis results when a fiber ring composed of a protein called actin around the center of the cell contracts pinching the cell into two daughter cells, each with one nucleus.In plant cells, synthesis of new cell wall between two daughter cells rather than cleavage furrow in cytoplasm
36 Asexual Reproduction A form of duplication using only mitosis. Example, a new plant grows out of the root or a shoot from an existing plant.Produces only genetically identical offspring since all divisions are by mitosis.
37 Sexual reproductionFormation of new individual by a combination of two haploid sex cells (gametes).Fertilization- combination of genetic information from two separate cells that have one half the original genetic informationGametes for fertilization usually come from separate parents
38 Female- produces an egg Male produces spermBoth gametes are haploid, with a single set of chromosomesThe new individual is called a zygote, with two sets of chromosomes (diploid).Meiosis is a process to convert a diploid cell to a haploid gamete, and cause a change in the genetic information to increase diversity in the offspring.
39 Chromosomes in a Diploid Cell Summary of chromosome characteristicsDiploid set for humans; 2n = 46Autosomes; homologous chromosomes, one from each parent (humans = 22 sets of 2)Sex chromosomes (humans have 1 set)Female-sex chromosomes are homologous (XX)Male-sex chromosomes are non-homologous (XY)
40 Number of sets of chromosomes in a cell Haploid (n)-- one set chromosomesDiploid (2n)-- two sets chromosomesMost plant and animal adults are diploid (2n)Eggs and sperm are haploid (n)
41 Most cells in the human body are produced by mitosis Most cells in the human body are produced by mitosis. These are the somatic (or vegetative) line cells.Cells that become gametes are referred to as germ line cells. The vast majority of cell divisions in the human body are mitotic, with meiosis being restricted to the gonads.
42 Diploid cells Haploid cells Characteristic number of chromosome pairs per cellHomologous chromosomesSimilar in length, shape, other features, and carry similar attributesHaploid cellsContain only one member of each homologous chromosome pair
44 Meiosis Diploid cells undergo meiosis to form haploid cells Meiosis potentially produces four haploid cellsMeiosis involves two separate divisions
45 Two successive nuclear divisions occur, Meiosis I (Reduction) and Meiosis II (Division). Meiosis I reduces the ploidy level from 2n to n (reduction) while Meiosis II divides the remaining set of chromosomes in a mitosis-like process (division).
46 In meiosis, homologous chromosomes are separated into different daughter cells Meiosis I and meiosis II each include prophase, metaphase, anaphase, and telophase
47 The First Division Meiosis I Prophase I is one of the most important stages of meiosis.During this stage, many crucial events occur.
48 In prophase I, The spindle appears. Nuclear envelopes disappear. The DNA of the chromosomes begin to twist and condense, making the DNA visible to the microscope.Each chromosome actively seeks out its homologous pair (which also has a sister chromatid).
49 The two replicated homologous pairs find each other and form a synapse The two replicated homologous pairs find each other and form a synapse. The structure formed is referred to as a tetrad (four chromatids).The point at which the two non-sister chromatids intertwine is called a chiasma. Sometimes a process known as crossing over occurs at this point.This is where two non-sister chromatids exchange genetic material. This exchange does not become evident, however, until the two homologous pairs separate.
51 Prophase I includes synapsis and crossing over Homologous chromosomes pair and undergo synapsisOne member of a pair is the maternal homologue, the other is the paternal homologueSynapsis is the association of four chromatids (two from each homologue)
52 In metaphase I, the tetrads line up along the equator. Anaphase I results in the separation of homologous pairs. Cells are haploid at this point.Telophase I results in a brief reappearance of nuclear envelopes, and the spindle disappears. The cell waits momentarily during interkinesis.Interkinesis separates meiosis I and II; no DNA synthesis occurs
53 The Second Division Meiosis II In prophase II, the spindle reappears, and the nuclear membrane fragments.In metaphase II, the chromosomes align at the equator.In anaphase II, sister chromatids separate.In telophase II, the nuclear envelopes reappear, and four haploid cells are the result.