Reproduction and Inheritance CH 8 Reproduction and Inheritance

Reproduction Asexual Reproduction Sexual Reproduction LM 340

Prokaryotes are asexual Via binary fission Recall that Prokaryotes have circular DNA Plasma membrane Prokaryotic chromosome Cell wall Duplication of chromosome and separation of copies 1 Continued elongation of the cell and movement of copies 2 Prokaryotic chromosomes Division into two daughter cells 3 Figure 8.3A

Eukaryotes Complex cell division Chromosomes occur as chromatin unless dividing Individual chromosomes visible when cell is dividing LM 600

Cell cycle Ordered sequence of events from time a cell is first formed until its own division Growth phase Division phase (mitotic phase) Mitosis Cytokinesis

INTERPHASE S (DNA synthesis) G1 G2 MITOTIC Fig. 8-5 INTERPHASE S (DNA synthesis) G1 G2 Cytokinesis Mitosis MITOTIC PHASE (M)

Interphase Synthesizes new organelles and molecules Growth phase Chromosomes duplicated Not individually distinguishable Loosely packed into chromatin Contains nucleoli indicating cell is making proteins

Prophase Chromatin fibers more tightly coiled and folded Form discrete chromosomes Nucleoli disappear Duplicated chromosomes appear and joined at centromere Mitotic spindle forms in cytoplasm

Prometaphase Nuclear envelope fragments and disappears Microtubules emerge from centrosome at poles ad reach chromosomes Chromosomes tightly condensed Kinetochore sppears

Metaphase Mitotic spindle formed Chromosomes line up at metaphase plate Centromeres of chromosomes line up

Anaphase Two centromeres of each chromosome come apart Sister chromatids separate Poles move farther apart, elongating cell Complete collection of chromosomes at each pole

Telophase and Cytokinesis Nucleear envelope reforms Chromosomes uncoil into chromatin Nucleoli reappear Cytokinesis Cell divides in two

INTERPHASE PROPHASE PROMETAPHASE Fig. 8-6a INTERPHASE PROPHASE PROMETAPHASE Centrosomes (with centriole pairs) Chromatin Early mitotic spindle Centrosome Fragments of nuclear envelope Kinetochore Centromere Nuclear envelope Plasma membrane Spindle microtubules Chromosome, consisting of two sister chromatids Nucleolus

TELOPHASE AND CYTOKINESIS Fig. 8-6b METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Nucleolus forming Metaphase plate Cleavage furrow Nuclear envelope forming Daughter chromosomes Spindle

Cytokinesis Cleavage Cell wall Starts in telophase or late anaphase Cleavage furrow Shallow groove on cell surface Microfilaments draw together and split cell in two Cell wall Vesicles containing cell wall material form cell plate Telophase Form cell plate that grows out to fuse with existing wall

Cytokenesis Cleavage furrow Microfilaments contract Cleavage furrow Contracting ring of microfilaments Daughter cells

Cell plate forming Daughter nucleus Wall of parent cell New cell wall Cell wall Vesicles containing cell wall material Cell plate Daughter cells

Cell Division Growth factors Density-Dependent inhibition Proteins that stimulate cell to divide Density-Dependent inhibition Stop cells from dividing under crowded conditions Anchorage dependence Need surface on which to divide

Growth Cell cycle control system Set of molecules that triggers and coordinates key events in cell cycle Checkpoints Cell is set to STOP until told to GO

Growth Cell cycle control system Set of molecules that triggers and coordinates key events in cell cycle G1 checkpoint G0 Control system S G1 M G2 M checkpoint G2 checkpoint

Growth factor Plasma membrane Relay proteins Receptor protein Fig. 8-9b Growth factor Plasma membrane Relay proteins Receptor protein G1 checkpoint Signal transduction pathway Control system G1 S M G2

Out of control Cancer Do not respond to cell control system No density-dependent inhibition Divide indefinitely No anchorage dependence

Meiosis terms Somatic cells Homologous chromosomes Sex chromosomes Autosomes Diploid Haploid

Haploid gametes (n = 23) n Egg cell n Sperm cell Meiosis Fertilization Fig. 8-13 Haploid gametes (n = 23) n Egg cell n Sperm cell Meiosis Fertilization Diploid zygote (2n = 46) 2n Multicellular diploid adults (2n = 46) Mitosis and development

Meiosis Produces haploid gametes in diploid organisms Duplication of chromosomes Two cell divisions

MEIOSIS I: Homologous chromosomes separate Fig. 8-14a MEIOSIS I: Homologous chromosomes separate INTERPHASE PROPHASE I METAPHASE I ANAPHASE I Centrosomes (with centriole pairs) Microtubules attached to kinetochore Metaphase plate Sister chromatids remain attached Sites of crossing over Spindle Nuclear envelope Sister chromatids Tetrad Centromere (with kinetochore) Homologous chromosomes separate Chromatin

MEIOSIS II: Sister chromatids separate Fig. 8-14b MEIOSIS II: Sister chromatids separate TELOPHASE II AND CYTOKINESIS TELOPHASE II AND CYTOKINESIS PROPHASE I METAPHASE II ANAPHASE II Cleavage furrow Sister chromatids separate Haploid daughter cells forming

(before chromosome duplication) Daughter cells of meiosis II Fig. 8-15 MITOSIS MEIOSIS Parent cell (before chromosome duplication) Site of crossing over MEIOSIS I Prophase I Prophase Tetrad formed by synapsis of homologous chromosomes Duplicated chromosome (two sister chromatids) Chromosome duplication Chromosome duplication 2n = 4 Chromosomes align at the metaphase plate Tetrads align at the metaphase plate Metaphase Metaphase I Anaphase Telophase Anaphase I Telophase I Sister chromatids separate during anaphase Homologous chromosomes separate (anaphase I); sister chroma- tids remain together Haploid n = 2 Daughter cells of meiosis I No further chromosomal duplication; sister chromatids separate (anaphase II) 2n 2n MEIOSIS II Daughter cells of mitosis n n n n Daughter cells of meiosis II

Diversity Random arrangement of homologous chromosomes Different gene versions Genetic recombination “Crossing over”

Error Abnormal sex chromosomes Trisomy 21 Nondisjunction in meiosis I meiosis II Gametes n + 1 n + 1 n – 1 n – 1 Number of chromosomes

Error Down syndrome Extra copy of chromosome 21