Mitosis / Meiosis / Reproduction: Asexual vs. sexual: Refer to Chapter 9 and sections of Chapter 10.

Transcription

1 Mitosis / Meiosis / Reproduction: Asexual vs. sexual: Refer to Chapter 9 and sections of Chapter Why do cells divide? For unicellular species, cell division is synonymous with reproduction and is essential in order to continue the species. For multicellular species, (like us) repeated cell division is necessary for growth, development and repair.. Another reason cells must divide is due to the cell s surface area to volume ratio. The smaller the surface area to volume ratio, the harder it is for a cell to take in nutrients or expel wastes fast enough to maintain homeostasis. REMEMBER: LSAVRB: Low Surface Area to Volume Ratio Bad. (Ex. 3:1 SAVR is bad) HSAVRG: High Surface Area to Volume Ratio Good (Ex. A 6:1 SAVR is good) 2. Define cell specialization and explain the pros/ cons associated with it. List the five levels of organization in multicellular organisms. NOTE: Excluding sperm and eggs, every cell in your body contains all the DNA necessary to make everything that is you. What is not understood is how, or when certain genes are turned on to create one cell type while others are turned off. In other words, why don t you have liver cells in your bones, or brain cells growing in your stomach? Cell growth is followed by specialization the ability of a cell to do a specific, unique function. The five levels or organization are listed below. Cell Tissue Organ Organ Systems Organism Single celled organisms must pay attention to all aspects of life. Cell specialization (also known as differentiation ) results in a division of labor. The human body has approximately 200 different cell types that have distinct roles. Although we do not know exactly when every cell starts to specialize, we do know that every organ in our body originates from one of three tissue layers that are formed within the first two weeks of development. These three layers are called ENDODERM, MESODERM an ECTODERM. See the next page for details on which organs are derived from each type of tissue.

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3 The advantage of cell specialization is that it results in a tremendous variety of life forms that can adapt and evolve as the earth changes. The disadvantage is that cells become interdependent on one another; meaning if one group of cells fail, this can have a domino effect on how the whole organism functions. 3. Explain what homologous chromosomes are. DNA is arranged into individual packages called chromosomes. In organisms that reproduce sexually, chromosomes occur in pairs. The chromosome number differs among species. Humans have 23 pairs of chromosomes (a total of 46 individually). They can be arranged from largest to smallest when viewed as a karyotype.

4 Of the 23 pairs, 22 are called autosomes and contain about 95% of the genes that spell out you. They are referred to as homologous pairs because they contain variations of the same genes in the same location. One member of each homologous pair comes from each parent. Any given trait you have is the result of how the genes on the homologous pairs are translated. In the example below, homologous chromosome pair #11 is shown below. The sign on each chromosome indicates where the hemoglobin gene is located. Notice, the gene is in the same location on each chromosome. A working copy of the gene (+) is what we want. The mutant form of the gene (-) leads to a mutation in the protein which causes sickle cell anemia. Look at the following ways that the gene can express itself in human beings: NOTE: one chromosome from each pair comes from each of your parents. The examples below show the different outcomes regarding the sickle cell trait. Person A Person B Person C Normal Hemoglobin Carrier for sickle cell anemia Has sickle cell anemia (Note: is does not matter which parent passed down the mutant gene)

5 Normal Hemoglobin Sickle Cell Hemoglobin The 23 rd pair is referred to as the sex chromosomes. These are not homologous. They are referred to as X and Y. They contain genes that are responsible for hormones that determine gender. If you are XX, (meaning you received one X chromosome from each parent), the stem cells in the developing gonads will become ovaries and female genitalia will form. If you are XY, (meaning you received an X chromosome from mom and a Y chromosome from dad), the stem cells in the developing gonads will become testes and male genitalia will form. IMPORTANT NOTE: The whole Y chromosome is not necessary to become male. There is a single control gene called the Sex determining Region or, (SRY gene). It is the presence or absence of SRY that determines what direction the premature gonad cells will go. The graphic below shows how the SRY gene can jump into an X chromosome and thereby form an XX male person or an XY female person

6 4. Explain the difference between haploid vs. diploid cells; somatic vs. sex cells The term haploid refers to a cell that has one member of a homologous pair/s of chromosomes. The symbol (N) is used to represent haploid cells. Gametes, (sperm and egg) are said to be haploid, or (N) and have 23 chromosomes (for humans). The term diploid refers to a cell that has both members of a homologous pair/s of chromosomes. The symbol (2N) is used to represent diploid cells. Somatic cells (all cells in your body that are NOT sperm or egg) are said to be diploid, or (2N) and have 46 chromosomes. For the Human Species Haploid = N = sex cells = 23 chromosomes Diploid = 2N = somatic cells = 46 chromosomes 5. Describe the different stages of a cell s lifecycle (Interphase, Mitosis (PMAT) and Cytokinesis). Compare animal mitosis to plant mitosis. Summarize the events in each one of the numbered stages below. Review the completed worksheet The Cell Cycle see my website slideshow on this topic.

7 6. Explain what stem cells are and how their applications in treating illness and disease. Embryonic stem cells are present in the very early stages of development and can become ANY cell type (the term for this is pluripotent). They can be grown in labs and appear to be immortal under laboratory conditions. Adult stem cells are those that have a predestined pathway and are necessary for growth and repair of tissues throughout one s life. A skin cell for example will always be a skin cell for the duration of that person s life. It has a finite number of divisions before that cell line dies. When enough adult stem cell lines die, the tissues and organs cannot function and the organism cannot survive. This is what is referred to as dying of natural causes. NOTE: Embryonic stem cells are easier to harvest but there is controversy about using human embryos as cell factories. Adult stem cells are harder to find and more difficult to keep alive. There are a variety of sources of stem cells that continue to be investigated. Recently, scientists have discovered a way to reboot normal body cells back to the pluripotent state, through genetic engineering. We can then guide their development into specific tissues. These are called induced pluripotent stem cells or ipsc s. The promise of using stem cells is to transplant them into damaged or diseased areas of the body and coax them to take on the role of the surrounding tissue or organ. Human stem cells are also being transplanted into other species to create chimeras; animal / human hybrids that are producing human proteins or perhaps one day human organs.

8 8. Define asexual reproduction. Provide examples of organisms that reproduce using the following methods: binary fission, budding and parthenogenesis. See the link on my website titled Asexual Reproduction. What are the pros and cons of reproducing sexually vs. asexually? BUDDDING VEGETATIVE PROPAGATION BINARY FISSION PARTHENOGENESIS (VIRGIN BIRTH)

9 9. Explain how cloning is done. Refer to the articles on my website and the questions you answered. 10. Define meiosis and explain its importance to organisms that reproduce sexually. How is it different from mitosis? Explain how male and female sex cells (also called gametes) are formed. See link on my website titled Meiosis 11. Define nondisjunction. Describe the following conditions caused by nondisjunction: Down s syndrome, Turner s syndrome, and Kleinfelter s syndrome. Read the PDF file on my website titled, Changes in Chromosome Numbers for details about these conditions.