5.4 Asexual Reproduction KEY CONCEPT Cells have distinct phases of growth, reproduction, and normal functions. 5.1 Cell Cycle

5.4 Asexual Reproduction Cells divide at different rates. The rate of cell division varies with the types of cells. 5.1 Cell Cycle

5.4 Asexual Reproduction KEY CONCEPT Cell cycle regulation is necessary for healthy growth. 5.3 Regulation of the Cell Cycle

5.4 Asexual Reproduction External factors include physical and chemical signals. Growth factors are proteins that stimulate cell division. 5.3 Regulation of the Cell Cycle

5.4 Asexual Reproduction Cell size is limited. If volume increases faster than surface area then cell divides 5.1 Cell Cycle

5.4 Asexual Reproduction –a normal feature of healthy organisms –occurs in development of infants webbed fingers Apoptosis is programmed cell death. 5.3 Regulation of the Cell Cycle

5.4 Asexual Reproduction KEY CONCEPT Many organisms reproduce by cell division.

5.4 Asexual Reproduction –Binary fission produces two daughter cells genetically identical to the parent cell. –occurs in prokaryotes (bacteria) parent cell DNA duplicates cell begins to divide daughter cells Asexual reproduction is the creation of offspring from a single parent.

5.4 Asexual Reproduction Budding forms a new organism from a small projection growing on the surface of the parent. bud Hydra Yeast

5.4 Asexual Reproduction Vegetative reproduction forms a new plant from the modification of a stem or underground structure on the parent plant.

5.4 Asexual Reproduction The cell cycle has four main stages. 5.1 Cell Cycle

5.4 Asexual Reproduction Interphase –Gap 1 (G 1 ): cell growth and normal functions Some cells (G0) – exit the cell cycle - fully developed cells in the CNS –Synthesis (S): copies DNA –Gap 2 (G 2 ): additional growth –Mitosis (M): includes division of the cell nucleus –cytokinesis - division of the cell cytoplasm 5.1 Cell Cycle

5.4 Asexual Reproduction Parent cell centrioles spindle fibers centrosome nucleus with DNA Mitosis produces two genetically identical daughter cells. 5.2 Mitosis and Cytokinesis

5.4 Asexual Reproduction Mitosis divides the cell’s nucleus in four phases. First phase –During prophase, chromosomes condense and spindle fibers form. Nucleolus and the nuclear membrane break down & disappear Centrioles (centrosomes) appear Centrioles move toward opposite poles of the cell 5.2 Mitosis and Cytokinesis

5.4 Asexual Reproduction

Second phase –During metaphase, chromosomes line up in the middle of the cell. –Chromosomes are easier to identify 5.2 Mitosis and Cytokinesis

5.4 Asexual Reproduction

Third phase –During anaphase, sister chromatids separate to opposite sides of the cell. 5.2 Mitosis and Cytokinesis

5.4 Asexual Reproduction

Fourth phase During telophase, the new nuclei form and chromosomes begin to uncoil. Spindle fibers disassemble 5.2 Mitosis and Cytokinesis

5.4 Asexual Reproduction

Cytokinesis differs in animal and plant cells. In animal cells, the membrane pinches closed –cleavage furrow In plant cells, a cell wall forms –cell plate 5.2 Mitosis and Cytokinesis

5.4 Asexual Reproduction Results of Mitosis 2 new cells genetically identical to the parent cell 2 identical diploid cells. Single celled eukaryote – asexual reproduction Multi-celled eukaryote – growth 5.2 Mitosis and Cytokinesis

5.4 Asexual Reproduction Meiosis makes haploid cells from diploid cells. –Meiosis occurs in sex cells - gametes –Meiosis produces genetically different gametes. 6.1 Chromosomes and Meiosis

5.4 Asexual Reproduction KEY CONCEPT During meiosis, diploid cells undergo two cell divisions that result in 4 different haploid cells. 6.2 Process of Meiosis

5.4 Asexual Reproduction Stages of Meiosis Interphase – G1, S, G2 Meiosis I 1.Prophase I DNA coils tightly into chromosomes Spindle fibers appear Nucleus & nucleolus disappear Every chromosome lines up next to its homologue – synapsis - each pair of homologous chromosome is called a tetrad – 4 chromatids XX - during synapsis the chromatids within a homolgous pair twist around each other – portions of chromatids may break off & attach to adjacent chromatids – crossing over * permits the exchange of genetic material between maternal & paternal chromosomes = genetic recombination 6.2 Process of Meiosis

5.4 Asexual Reproduction 6.6 Meiosis and Genetic Variation

5.4 Asexual Reproduction Metaphase I Tetrads line up randomly along the middle of the cell 6.6 Meiosis and Genetic Variation

5.4 Asexual Reproduction Anaphase I Tetrads separate Each homologous chromosome moves to an opposite pole Independent Assortment – random separation of the homologous = genetic recombination 6.6 Meiosis and Genetic Variation

5.4 Asexual Reproduction Telophase I Chromosome reach the opposite pole Cytokinesis begins Each new cells contain a haploid # of chromosomes (half the original #) 6.6 Meiosis and Genetic Variation

5.4 Asexual Reproduction DNA is not replicated between meiosis I and meiosis II (No Interphase) 6.2 Process of Meiosis

5.4 Asexual Reproduction Meiosis II 1.Prophase II Spindle fibers and centrioles form 2.Metaphase II Chromosomes move to the middle of the cells 3.Anaphase II Chromatids separate & move toward opposite poles 4.Telophase II Nuclear membrane forms around the chromosomes Cytokinesis II – results in 4 new cells each with half the # of chromosomes 6.2 Process of Meiosis

5.4 Asexual Reproduction –Meiosis has two cell divisions while mitosis has one. –Meiosis results in haploid cells; mitosis results in diploid cells. 6.2 Process of Meiosis

5.4 Asexual Reproduction Haploid cells develop into mature gametes. Gametogenesis is the production of gametes. Gametogenesis differs between females and males. 6.2 Process of Meiosis

5.4 Asexual Reproduction Spermatogenesis – production of sperm cells Diploid reproductive cell divides to form four haploid cells – spermatids Each spermatid then develops into a mature sperm cell sperm cells – spermatozoa 6.2 Process of Meiosis

5.4 Asexual Reproduction Oogenesis – production of mature egg cells - ova Diploid reproductive cell divides to produce one mature egg cell (ovum) During cytokinesis I & II the cytoplasm of the cell is divided unequally One cell receives most of the cytoplasm and develops into a mature egg cell Other 3 products = polar bodies = degenerate (break down) 6.2 Process of Meiosis