CH 8 Reproduction and Inheritance

Reproduction Asexual Reproduction Sexual Reproduction LM 340 

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

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

Chromosomes DNA organizes into chromosomes – Chromosomes duplicate as cell prepares to divide – After duplication, each chromosome consists of 2 sister chromatids Constricted at centromere 23 pair of homologous chromosomes in humans

Fig. 8-4bc Sister chromatids Centromere Chromosome duplication Sister chromatids Chromosome distribution to daughter cells

Mitosis & Meiosis Mitosis- nuclear division that maintains chromosome numbers Meiosis- nuclear division that halves the chromosome number

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

Fig. 8-5 S (DNA synthesis) G1G1 G2G2 Cytokinesis Mitosis I NTERPHASE M ITOTIC PHASE (M)

Interphase G1 – Cell growth before DNA replication – Contains nucleoli indicating cell is making proteins S – DNA replication G2 – Second stage of growth before division – Make proteins to drive mitosis

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 Some cells stuck in “stop”, i.e. nerve cells always in G1

Mitosis Prophase Metaphase Anaphase Telophase Cytokinesis

Prophase Chromatin fibers more tightly coiled and folded – Form discrete chromosomes – Nucleoli disappear – Duplicated chromosomes appear and joined at centromere – Nuclear envelope beings to dissolve Centromsomes duplicate and move to opposite ends of nucleus – Mitotic spindle forms in cytoplasm

Prophase

Mitotic Spindle Centrosome – Region near the nucleus that organizes microtubules – Two barrel-shaped centrioles (not found in plant cells) – Microtubules grow from centrosome to form a spindle The spindle attaches to and moves chromosomes during nuclear division – Attach to chromosome at kinetochore – Attach to cell wall – Add or loose subunits to push and pull chromosomes apart

Prometaphase/Metaphase Nuclear envelope fragments and disappears Kinetochore visible Mitotic spindle formed and microtubules attach to sister chromatids Chromosomes line up at metaphase plate Centromeres of chromosomes line up

Fig. 8-6ad PROMETAPHASE METAPHASE

Anaphase Two centromeres of each chromosome come apart – Motor proteins on spindle drag chromatids apart Sister chromatids separate Poles move farther apart, elongating cell Complete collection of chromosomes at each pole

ANAPHASE

Telophase – Nuclear envelope reforms – Chromosomes uncoil into chromatin – Nucleoli reappear Cytokinesis – Cell divides in two

TELOPHASE

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

Fig. 8-6b Metaphase plate Nucleolus forming METAPHASETELOPHASE AND CYTOKINESISANAPHASE Cleavage furrow Daughter chromosomes Nuclear envelope forming Spindle

Fig. 8-5b (6), p. 141 Stepped Art 6) Telophase The chromosomes reach the spindle poles and decondense. A nuclear envelope forms around each cluster. Mitosis is over. centrosome 1) Early Prophase Mitosis begins. In the nucleus, the DNA begins to appear grainy as it organizes and condenses. The centrosome is duplicated. 2) Prophase The chromosomes become visible as distinct structures as they condense further. Microtubules assemble and move one of the two centrosomes to the opposite side of the nucleus, and the nuclear envelope breaks up. pole 3) Transition to Metaphase The nuclear envelope is gone, and the chromosomes are at their most condensed. Spindle microtubules assemble and attach sister chromatids to opposite spindle poles. microtubule of spindle 4) Metaphase All of the chromosomes are aligned midway between the spindle poles. Microtubules attach each chromatid to one of the spindle poles, and its sister to the opposite pole. 5) Anaphase Motor proteins moving along spindle microtubules drag the chromatids toward the spindle poles, and the sister chromatids separate. Each sister chromatid is now a separate chromosome.

Cytokinesis Cleavage- Animal cells – Starts in telophase or late anaphase – Cleavage furrow Shallow groove on cell formed via contractile ring Microfilaments draw together and split cell in two Cell wall – Vesicles containing cell wall material form cell plate Form cell plate that grows out to fuse with existing wall

Cytokinesis

Cytokenesis Cleavage furrow Cleavage furrow Contracting ring of microfilaments Daughter cells Cell plate Cell wall Vesicles containing cell wall material Wall of parent cell New cell wall Daughter cells Cell plate forming

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

G 1 checkpoint Control system M S G2G2 G1G1 M checkpoint G 2 checkpoint G0G0 Cell cycle control system Set of molecules that triggers and coordinates key events in cell cycle Control

Fig. 8-9b G 1 checkpoint Control system M S G2G2 G1G1 Receptor protein Signal transduction pathway Relay proteins Plasma membrane Growth factor

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

Meiosis terms Somatic cells- non-reproductive cells Gametes- reproductive cells (sex cells) Homologous chromosomes- chromosomes with same genes at same loci Sex chromosomes- determine sex Autosomes- non-sex chromosomes Diploid- 2 sets of chromosomes Haploid- single set of chromosomes Alleles- different forms of the same gene

Fig Haploid gametes (n = 23) n Egg cell Sperm cell Fertilization Meiosis Multicellular diploid adults (2n = 46) Mitosis and development n 2n2n2n2n Diploid zygote (2n = 46)

Meiosis Produces haploid gametes in diploid organisms Duplication of chromosomes – Two cell divisions – Form a tetrad

Crossing over A chromosome and its homologous partner exchange a corresponding piece of DNA crossover

Fig. 8-10a, p. 146

Fig. 8-10b, p. 147

Fig Prophase Metaphase I Metaphase 2n = 4 Tetrads align at the metaphase plate Duplicated chromosome (two sister chromatids) Parent cell (before chromosome duplication) Chromosome duplication Chromosomes align at the metaphase plate Anaphase Telophase Sister chromatids separate during anaphase Daughter cells of mitosis 2n2n 2n2n n Chromosome duplication Site of crossing over Tetrad formed by synapsis of homologous chromosomes M EIOSIS Prophase I Anaphase I Telophase I M ITOSIS M EIOSIS I Haploid n = 2 Daughter cells of meiosis I M EIOSIS II n nn Daughter cells of meiosis II Homologous chromosomes separate (anaphase I ); sister chroma- tids remain together No further chromosomal duplication; sister chromatids separate (anaphase II )

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

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

Error Down syndrome – Extra copy of chromosome 21

Videos Overview – =related =related – e=related Cytokinesis – Meiosis – mQS_FZ0&feature=related mQS_FZ0&feature=related – e=related

Videos Mutations and DNA edia#p/u/43/hkK5hDbxJ0M