Mitosis, Meiosis, and Life Cycles Chapter 12

KEY TERMS DIPLOID (2N) DIPLOID (2N) The condition of having two sets of chromosomes per nucleus The condition of having two sets of chromosomes per nucleus In somatic cells of diploid organisms, chromosomes are present in pairs In somatic cells of diploid organisms, chromosomes are present in pairs HAPLOID (N) HAPLOID (N) The condition of having one set of chromosomes per nucleus The condition of having one set of chromosomes per nucleus

KEY TERMS HOMOLOGOUS CHROMOSOMES HOMOLOGOUS CHROMOSOMES Members of a chromosome pair that are similar in size, shape, and genetic constitution Members of a chromosome pair that are similar in size, shape, and genetic constitution

KEY TERMS CELL CYCLE CELL CYCLE Cyclic series of events in the life of a dividing eukaryotic cell Cyclic series of events in the life of a dividing eukaryotic cell

KEY TERMS INTERPHASE INTERPHASE Stage of the cell cycle between successive mitotic divisions Stage of the cell cycle between successive mitotic divisions

Interphase During interphase During interphase cell grows and prepares for next division cell grows and prepares for next division DNA replicates DNA replicates Interphase is divided into Interphase is divided into first gap phase (G 1 ) first gap phase (G 1 ) synthesis phase (S) synthesis phase (S) second gap phase (G 2 ) second gap phase (G 2 )

KEY TERMS MITOSIS MITOSIS Division of the cell nucleus resulting in two daughter nuclei, each with the same number of chromosomes as the parent nucleus Division of the cell nucleus resulting in two daughter nuclei, each with the same number of chromosomes as the parent nucleus

KEY TERMS CYTOKINESIS CYTOKINESIS Stage of cell division in which the cytoplasm divides to form two daughter cells Stage of cell division in which the cytoplasm divides to form two daughter cells

Cell Cycle

Stages of Mitosis Prophase Prophase Metaphase Metaphase Anaphase Anaphase Telophase Telophase

Prophase Chromatin condenses into chromosomes Chromatin condenses into chromosomes Nucleolus disappears Nucleolus disappears Nuclear envelope breaks down Nuclear envelope breaks down Mitotic spindle begins to form Mitotic spindle begins to form At the end of prophase, each duplicated chromosome is composed of two sister chromatids At the end of prophase, each duplicated chromosome is composed of two sister chromatids

A Duplicated Chromosome

KEY TERMS SPINDLE SPINDLE Structure consisting mainly of microtubules that provides the framework for chromosome movement during cell division Structure consisting mainly of microtubules that provides the framework for chromosome movement during cell division

Metaphase Duplicated chromosomes line up along midplane of cell Duplicated chromosomes line up along midplane of cell

Anaphase Sister chromatids separate and move to opposite poles of the cell Sister chromatids separate and move to opposite poles of the cell Each chromatid is now a separate chromosome Each chromatid is now a separate chromosome

Telophase Nuclear envelope forms around each set of chromosomes Nuclear envelope forms around each set of chromosomes Nucleoli reappear Nucleoli reappear Chromosomes lengthen and become chromatin Chromosomes lengthen and become chromatin Spindle disappears Spindle disappears

KEY TERMS CELL PLATE CELL PLATE Structure that forms during cytokinesis in plants, separating two daughter cells produced by mitosis Structure that forms during cytokinesis in plants, separating two daughter cells produced by mitosis Cytokinesis generally takes place in telophase Cytokinesis generally takes place in telophase

Cytokinesis

Interphase and Mitosis

(a) Interphase(b) Prophase Condensing chromosome (consists of 2 sister chromatids) (d) Anaphase Sister chromatids (now called chromosomes) move to opposite ends of cell (e) Telophase New nuclei Cell plate Fig. 12-2, p. 244 (c) Metaphase Spindle microtubules Stepped Art

KEY TERMS MEIOSIS MEIOSIS Process in which a 2n cell undergoes successive nuclear divisions, potentially producing four n nuclei Process in which a 2n cell undergoes successive nuclear divisions, potentially producing four n nuclei Leads to formation of spores in plants Leads to formation of spores in plants

Meiosis Meiosis must occur at some time in the life of a sexually reproducing organism if gametes are to be haploid Meiosis must occur at some time in the life of a sexually reproducing organism if gametes are to be haploid Meiosis consists of two cell divisions Meiosis consists of two cell divisions Meiosis I Meiosis I Meiosis II Meiosis II

Meiosis I Members of each homologous pair of chromosomes separate and are distributed into separate nuclei in two daughter cells Members of each homologous pair of chromosomes separate and are distributed into separate nuclei in two daughter cells Chromosomes were duplicated prior to meiosis I, so each consists of two chromatids Chromosomes were duplicated prior to meiosis I, so each consists of two chromatids

Meiosis II Chromatids separate into individual chromosomes and are distributed into different haploid daughter cells Chromatids separate into individual chromosomes and are distributed into different haploid daughter cells Four haploid cells form Four haploid cells form

KEY TERMS SYNAPSIS SYNAPSIS Physical association of homologous chromosomes during prophase I of meiosis Physical association of homologous chromosomes during prophase I of meiosis

Crossing Over Crossing over Crossing over Exchange of segments of homologous chromosomes Exchange of segments of homologous chromosomes Synapsis and crossing over occur during prophase I of meiosis Synapsis and crossing over occur during prophase I of meiosis

Crossing Over

Meiosis

Meiosis

LEARNING OBJECTIVE Compare and contrast mitosis and meiosis Compare and contrast mitosis and meiosis

Mitosis Involves a single nuclear division in which the two daughter cells formed are genetically identical to each other and to the original cell Involves a single nuclear division in which the two daughter cells formed are genetically identical to each other and to the original cell Synapsis of homologous chromosomes does not occur during mitosis Synapsis of homologous chromosomes does not occur during mitosis

Meiosis Involves two successive nuclear divisions and forms four haploid cells, each with a different combination of genes Involves two successive nuclear divisions and forms four haploid cells, each with a different combination of genes Synapsis of homologous chromosomes occurs during prophase I of meiosis Synapsis of homologous chromosomes occurs during prophase I of meiosis

Mitosis and Meiosis

KEY TERMS Alternation of generations Alternation of generations Plants alternate haploid and diploid generations Plants alternate haploid and diploid generations SPOROPHYTE SPOROPHYTE 2n, spore-producing stage in plant life cycle 2n, spore-producing stage in plant life cycle GAMETOPHYTE GAMETOPHYTE n, gamete-producing stage in plant life cycle n, gamete-producing stage in plant life cycle

The Sporophyte The 2n, spore-producing stage in the life cycle of a plant The 2n, spore-producing stage in the life cycle of a plant A diploid sporophyte plant forms haploid spores by meiosis A diploid sporophyte plant forms haploid spores by meiosis A spore divides mitotically to form a haploid gametophyte plant A spore divides mitotically to form a haploid gametophyte plant

The Gametophyte The n, gamete-producing stage in the life cycle of a plant The n, gamete-producing stage in the life cycle of a plant The gametophyte produces haploid gametes by mitosis The gametophyte produces haploid gametes by mitosis Two gametes fuse to form a diploid zygote, which divides mitotically to produce a diploid sporophyte Two gametes fuse to form a diploid zygote, which divides mitotically to produce a diploid sporophyte

Plant Life Cycle