Reproduction. Part 1

Transcription

1 Reproduction Part 1

2 Reproduction Reproduction and development are necessary for the continuation of any species. Every organism requires a set of coded instructions (their chromosomes) for specifying it s traits. For offspring (children) to resemble their parents there must be a reliable way to transfer the information on the chromosomes from one generation to the next. This may be accomplished by asexual reproduction (one parent) or sexual reproduction (two parents). Hereditary information is contained in the genes, located in the chromosomes in each cell. I. Types of reproduction: Asexual reproduction (without sex) 1. Only one parent. 2. No fusion (joining together) of cells or cell nuclei. 3. No special reproductive cells (eggs and sperm) or organs involved.

3 4. The two cells produced are identical to each other and identical to the parent cells. 5. Another name for asexual reproduction is. Cloning In cloning a somatic cell (body cell) is used to create a genetically identical organism. The first successful cloning of a mammal occurred in 1996 at the Roslin Institute in Scotland 1. A donor cell is taken from a sheep s udder 4. These two cells are fused using and electric shock 2. An egg cell is taken from an adult female sheep 3. The nucleus of the egg cell is removed 5. The fused cell begins dividing normally 7. The embryo develops normally into a lamb- Dolly 6. The embryo is placed in the uterus of a foster mother

4 reproduction. Sexual 1. Two parents are involved. 2. Fusion (joining together) of two nuclei from specialized sex cells which are produced by two separate parents (for example the fusion of egg and sperm cells to produce an embryo) 3. Special reproductive cells (eggs and sperm) or organs (ovaries and testes) are involved. 4. The offspring inherit characteristics of both parents, and this allows for variation in the offspring

5 II. Mitotic Cell Division- This process is used for two purposes: 1. Reproduction in one-celled organisms. 2. Repair and growth of body (somatic) cells in multicellular organisms. Mitotic Cell Division involves two steps: 1. Mitosis - complex changes in the nucleus involving replication of the chromosomes and separation of these chromosomes into two identical sets (nuclei)

6 2. Cytoplasmic division - the separation of cytoplasm which occurs during or at the end of mitosis, resulting in the formation of two daughter cells each containing a nucleus with an identical set of chromosomes.

7 Interphase- Chromosomes are replicating Parent Cell Chromatin condenses into chromosomes. Nuclear envelope disappears Chromosomes align at the equatorial plate Sister chromosome separate. Centomeres divide Chromatin expands. Cytoplasm divides Two daughter cells

8 Mitosis is divided into stages or. phases 1. - Interphase Duplication of chromosomes, chromatids are attached at the centomere in the center of the doubled chromosome. DNA is packed with proteins to form chromatin Chromosome Two chromatids Centomere 2. Prophase - Centrioles (animal cells) separate, spindles form, nucleolus disappears, the nuclear membrane begins to disappear, chromatids shorten and thicken.

9 3. - Metaphase chromosomes line up (meet) on the equatorial plane, centromere replicates Anaphase daughter chromosomes move to opposite poles (away) Telophase chromosomes uncoil back to chromatin, spindle fibers, disappear nuclear membrane forms, cytoplasm divides (cytokinesis) (in plants cells, cell plate forms). AS A RESULT OF MITOTIC CELL DIVISION, TWO IDENTICAL DAUGHTER CELLS ARE PRODUCED. THEY ARE IDENTICAL TO EACH EACH OTHER AND TO THE PARENT CELL!

10 This diagram shows a human cell that has undergone Mitosis. Notice that two cells are produced. Each has 46 chromosomes and are identical to the parent cell. Plant Cell Mitosis: 1. Mitosis in Plants occurs in developing seeds and in growing regions of roots and stems. 2. Differences in plant and animal cell mitosis: a) No, centrioles but spindle fibers do form. b) In telophase there is no pinching of the cytoplasm. Instead a Cell plate forms which becomes the cell wall.

11 Plant cell Mitosis

12 Comparisons between Plant and Animal Cell Mitosis Plant Cells centrioles No Cytoplasm divides by forming a Cell plates Animal Cells centrioles Have Cytoplasm divides by Pinching in of cell membrane (cytokinesis)

13 Cancer cell growth Cancer - Uncontrolled, abnormal, rapid mitotic cell division. This abnormal cell division invades surrounding tissues and interferes with normal tissue and organ function

14 Types of asexual reproduction (involves only mitosis) A. Binary Fission 1. The simplest form of asexual reproduction 2. The parent organism divides into two equal parts. 3. Results in two daughter cells that become a separate individual and grow to normal size. 4. This is the usual method of reproduction in single celled organisms. Binary Fission

15 B. Budding 1. In unicellular organisms such as yeast, budding is similar to fission except that the cytoplasmic division is. unequal 2. New individuals develop as small outgrowths or buds on the outer surface of the parent. 3. These buds may break off and live independently or remain together to form a. colony Budding in yeast

16 4. Budding in the hydra produces a multicellular outgrowth (a new hydra) from the parent organism. This little hydra then breaks away from the parent but is genetically identical.

17 C. Sporulation or spore formation. 1. Spores are small, microscopic, specialized cells which contain a nucleus and a small amount of cytoplasm surrounded by a thick outer wall. spores Moldy bread

18 2. These are released from Spore cases. 3. Spores can resist unfavorable environmental conditions (extreme heat and cold). When the conditions are favorable the spore can produce a new organism. 4. Bacteria, yeasts, molds mushrooms, mosses and ferns produce spores. D. Regeneration 1. The development of a whole new organism from a part of the original organism. 2. Regeneration also refers to the replacement of lost structures for example: Lobsters may regenerate a lost claw.

19 3. Organisms that can regenerate have many cells that are undifferentiated meaning they have not yet been assigned a job. This lobster has regenerated a new claw. This lizard will regenerate a new tail lost perhaps in a fight Whole starfish regenerating from a lost leg D. Vegetative - propogation When an entire new plant can grow from a runner or a. bud Examples: Potatoes and strawberries

20 Vegetative Propagation in Strawberries Mother plant Daughter plant genetically identical to mother. Vegetative propagation in potato plant The roots will develop into another potato plant genetically identical to the original.