Reproduction & Development. 1 parent cell divides to form 2 daughter cells All offspring have exact same DNA as parent

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1 Living Environment Dr. Golub Reproduction & Development Asexual reproduction 1 parent cell divides to form 2 daughter cells All offspring have exact same DNA as parent Sexual Reproduction Requires 2 parents that contribute full sets of genes Genes recombine, so offspring is similar to both parent cells, but has differences as well. Key Terms Binary Fission Budding Sporulation Regeneration Runner Bulb Tuber Stem Cutting Grafting Asexual Reproduction (Mitosis) Cell Growth Cells grow until they reach their size limit, then they either stop growing, or divide. Cells have size limitations. The key factor that regulates the size of a cell is the ratio of its surface area to its volume. Surface Area = cell membrane Volume = space taken up inside the cell. If a cell grows too big, it may have difficulty supplying nutrients and expelling enough waste products.

2 Why are new cells made? Growth Repair How are new cells made? Cell Theory states All cells arise from pre- existing cells This process takes place through cell division. Cell Division 2 steps o Mitosis Nucleus divides o Cytokinesis Cytoplasm divides We end with two identical cells Asexual Reproduction Involves only one parent Nucleus The control center of the cell Also plays a major role in cell division Before mitosis begins, a series of changes takes place in the nucleus. Results in duplication of hereditary material Nuclear Division When a nucleus divides, each new nucleus is called a daughter nucleus. Each new nucleus contains a complete copy of the original nucleus. DNA

3 Deoxyribonucleic acid The hereditary material of the cell Contains the information needed to make the parts of each cell Contains the information that determines how the organism is made up and works Chromosomes DNA exists in a mass of thin, twisted threads called chromatin Chromatin is made of DNA wound around a small group of proteins called histones In cells undergoing mitosis, chromatin shortens and thickens into rod- like structures called chromosomes Chromosomes Each type of organisms has a specific number of chromosomes in each body cell. Humans = 46 Wheat = 42 Potatoes = 48 Crayfish = 20 Fruit flies = 8 The Stages of Mitosis

4 Mitosis The duplication and division of the nucleus of a cell and its chromosomes during cell reproduction Body cells reproduce through mitosis o All cells of the body EXCEPT for sex cells (gametes) Gametes (sperm and egg) reproduce through another process Meiosis The Cell Cycle The process by which cells grow and divide. Most cells will divide. Each time a cell completes a cycle, it becomes 2 cells.

5 3 main stages o Interphase Cell growth, function, and DNA replication o Mitosis Cell s nucleus divides o Cytokinesis Cytoplasm divides, forms a new cell The duration of the cell cycle varies, between 8 minutes to many years, but for most cells, it s about hours. o Stage 1 = Interphase The resting phase? Cells grow Cells carry out normal functions DNA is replicated 3 stages of interphase G1 = Growth S = DNA is replicated o Chromosomes = structures that contain genetic information. o Chromatin = relaxed form of DNA G2 = nucleus prepares to divide o Stage 2 = Mitosis Cell s nucleus divides Occurs as a continuous process, but can be separated into 4 steps. Prophase Metaphase Anaphase Telophase PMAT

6 o Prophase 1 st stage Longest phase Chromatin tightens and condenses into chromosomes (shaped like an X ) Each chromosome is a single structure that contains genetic material that was replicated during interphase. Each half of the X is called a sister chromatid Sister chromatids contain identical copies of DNA, attached at the centromere. Nucleolus disappears Spindle fibers form in the cytoplasm Centrioles migrate to the poles of the cell Nuclear envelope disappears Spindle fibers attach to sister chromatids of each chromosome

7 o Metaphase 2 nd stage Short stage Sister chromatids line up along the equator o Anaphase 3 rd stage Chromatids are pulled apart This ensures that each new cell will get the same genetic information. o Telophase 4 th stage Chromosomes arrive at poles Two new nuclear membranes form o Stage 3 = Cytokinesis Cytoplasm divides Forms two new cells Plant Cells The main events of mitosis are basically the same as in the animal cell EXCEPT: o No centrioles o Cell walls do not pinch in o Instead a cell plate forms across the middle and joins cell wall, dividing cell in half

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9 Types of Asexual Reproduction Binary Fission Budding Spore Formation Regeneration Vegetative Propagation Binary Fission The simplest form of asexual reproduction Parent organism divides into two equal parts Each part then grows to normal size No parent is left Seen in one celled organisms o Bacteria, protozoa, and many algae Bacteria Bacteria have no organized nucleus Hereditary material is a single, circular chromosome First, the chromosome attaches to cell membrane and replicates A cell wall forms between the chromosome and its copy The wall divides the cell into two daughter cells The cells grow before dividing Can divide every 20 minutes

10 Budding The parent organism divides into two unequal parts New individuals are seen as small outgrowths, or buds Buds can break off and live independently Buds can remain attached, forming a colony Takes place in hydra, yeast, sponges, and some worms Spore Formation Also called sporulation Spores are single, specialized cells produced by certain organisms Spores are released from parent organisms and germinate and grow to form new individuals Spores usually surrounded by a thick, hard outer wall Seen in algae, fungi, and protozoa Bread Mold o Bread mold is a fungus o Dark, cottony mass on bread and other foods o Spores are produced through mitotic cell division inside a spore case o Thousands of black spores within each spore case o When grown, the wall of spore case breaks down, and spores are carried by air currents o When a spore lands in an environment with warmth, food, and moisture, it germinates and grows

11 Regeneration The ability of an organism to regrow lost body parts Seen in hydra, planaria, starfish, and earthworm Mammals have limited regeneration capabilities Vegetative Propagation Most plants reproduce sexually by means of seeds, asexual reproduction involving vegetative structures: roots, stems, and leaves Normally play a part in plant nutrition Undifferentiated cells divide through mitosis, then differentiate to produce a new individual plant Occurs naturally and artificially o Naturally Bulbs Tubers Runners Rhizomes o Artificially Cutting Grafting

12 Bulbs o Short underground stems o Tulips, onions and lilies have bulbs Tubers o Enlarged part of an underground stem o White potatoes o eyes grow out as shoots and produce roots Runners o Sideways stems with buds along soil surface o Strawberries Rhizomes o Thick sideways stems underground o Ferns, irises, cattails, and water lilies Cutting o A vegetative part (stem, leaf, or root) is used to produce a new individual

13 Grafting o A stem or bud is removed from one plant and joined permanently to the stem of a closely related plant o Used to propagate apples, roses, peaches, plums, grapes, and seedless fruits. Karyotypes The complete set of chromosomes in the cells of an organism Often studied when the cell is in metaphase Arranged and numbered by size, largest to smallest The karyotype of the human female contains 23 pairs of homologous chromosomes: o 22 pairs of autosomes o 1 pair of X chromosomes The karyotype of the human male contains: o the same 22 pairs of autosomes o one X chromosome o one Y chromosome

14 Meiosis Key Terms Parthenogenesis Sexual Reproduction (Meiosis) Synapsis Tetrad Disjunction Crossing Over Our Cells 2 major categories o Body Cells (somatic cells) Nerve cells, muscle cells, skin cells, etc. Review o Sex Cells (gametes) (germ cells) Sperm cells & egg cells Each of us has characteristics passed on from our parents. Each characteristic (hair color, eye color, height, etc.) is called a trait. The instructions for each trait are located on the chromosomes, inside the nucleus of each cell. DNA segments on each chromosome are called genes. Each chromosome consists of hundreds of genes.

15 Homologous Chromosomes Each human body cell has 46 chromosomes. Each parent contributes 23 chromosomes. The result is 23 pair, or 46. The chromosomes that make up a pair, one from each parent, are called homologous chromosomes. Have the same length Have the same centromere position Carry genes that contain the same inherited traits Haploid & Diploid Cells In order to maintain the correct number of chromosomes from generation to generation, an organism produces gametes. Gametes are sex cells with half the number of chromosomes. In humans, gametes contain 23 chromosomes The letter n is used to represent the number of chromosomes in a gamete. A cell with n number of chromosomes is called a haploid cell. When one haploid cell from a female (egg cell) joins with one haploid cell from the male (sperm cell) it is called fertilization. As a result of fertilization, the number of chromosomes becomes 2n. 2n = a diploid cell Meiosis Gametes are formed during a process called meiosis. Meiosis is a type of cell division that reduces the number of chromosomes. Also called reduction division. Mitosis maintains the number of chromosomes; meiosis reduces the number by half.

16 Meiosis Meiosis involves TWO consecutive cell divisions o Meiosis I o Meiosis II Meiosis I Interphase o Same as for mitosis o Cells carry out regular functions, growing, preparing to divide. o DNA is replicated PMAT

17 Prophase I Replicated chromosomes become visible The replicated chromosomes consist of two sister chromatids. The nuclear envelope dissolves Spindles form Synapsis o Pairing o Homologous pairs find each other Crossing over can occur. o chromosomal segments are exchanged between a pair of homologous chromosomes. Metaphase I Pairs of homologous chromosomes line up at the equator (recall that in mitosis, individual chromosomes lined up at the equator) Spindle fibers attach to the centromere of each homologous chromosome Anaphase I Pairs of homologous chromosomes separate Each member of the pair is guided by spindle fibers to opposite poles of the cell. As this happens the chromosome number is reduced from 2n to n. Recall that in mitosis, sister chromatids pull apart here, but in meiosis, each homologous chromosome still consists of two sister chromatids.

18 Telophase I Homologous chromosomes (consisting of 2 sister chromatids) reach opposite poles. Sister chromatids may not be identical because crossing over may have occurred in prophase I. Cytokinesis occurs during telophase I. End of Meiosis I Recall that mitosis ended with cytokinesis and then interphase. Meiosis also starts with interphase, but after telophase I and cytokinesis, there is little or NO INTERPHASE, so the DNA is NOT REPLICATED between meiosis I and meiosis II. Meiosis II Prophase II Spindles appear, chromosomes condense Metaphase II Chromosomes at the equator (haploid number) Centromeres split apart Anaphase II Sister chromatids that were pulled apart at the centromere now move to opposite poles Telophase II Chromosomes reach the poles Nuclei reform Cytokinesis occurs after telophase II, resulting in 4 haploid cells, each with n number of chromosomes

19 Mitosis One cell division occurs DNA replication occurs during interphase Meiosis Two sets of divisions occur; meiosis I and meiosis II DNA replication occurs ONCE, before meiosis I Two identical cells are formed per cycle The daughter cells are genetically identical Occurs in body cells Involved in growth and repair Four haploid (n) cells are formed per cycle The daughter cells are not genetically identical due to crossing over Occurs in reproductive cells Involved in production of gametes and providing genetic variation in organisms

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