Unit 5 Section 2. Chromosome

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1 Unit 5 Section 2 Evidence 9: using figure 1 on page 234, Answer the question. Describe what happens to the part of the planarian that was amputated. How does this piece change over time? Evidence 10: How do you think organisms like the planarian regenerate parts of their body? How could humans benefit from this knowledge? Chromosome a long continuous thread of DNA that consists of numerous genes along with regulatory information human cells have 46 chromosomes if stretched out and laid end to end it would be 10 feet long because such a long strand it wraps tightly around a protein to help condense it o the proteins are called histones o looks similar to beads on a string during interphase DNA looks like spaghetti, loosely organized o called chromatin when like this during mitosis they are tightly condensed Parts of a chromosome looks similar to an X the left and right halves of the X are identical one half of the chromosome is called a chromatid together the two identical chromatids are called sister chromatids sister chromatids are held together at the centromere o part that looks pinched the ends of the chromosomes are called telomeres Evidence 11: DNA must be coiled into special structures before a cell divides. Why do you think it is necessary for the DNA to be structured this way before cell division occurs?

2 Evidence 12: Every cell in your body originated from one cell. What does this mean about the DNA in each of your body cells? Cell Cycle in detail Interphase provides critical time for the duplication of organelles and for DNA replication by the end an individual cell has two full sets of DNA, or chromosomes, and is large enough to divide Mitosis divides a cell s nucleus into two genetically identical nuclei, each with its own single, full set of DNA 4 main phases of mitosis 1. Prophase: During the prophase stage of mitosis the duplicated DNA condenses into compact structures known as chromosomes. Remember the DNA has already been duplicated. While the DNA is condensing into chromosomes, the nuclear envelope surrounding the DNA begins to break down. This happens so the DNA compacted into these chromosome structures can be accessed by the rest of the cell. 2. Metaphase: In the metaphase stage of mitosis the chromosomes align in the center of the cell called the equatorial plate (like the equator of the Earth). Organelles known as centrioles move to the polar ends of the cell and project thin spindle fibers to connect to the center (centromeres) of each chromosome. Essentially the cell is grabbing each chromosomes at its center so it can pull it into equal pieces. 3. Anaphase: While in the anaphase stage of mitosis the centrioles will begin to pull each chromosome into two halves called sister chromatids. Each chromatid contains the same information.

3 4. Telophase: Finally in the Telophase stage of mitosis the nuclear membrane forms around the chromatids and they are completely located at opposite ends of the cell. Cytokinesis: Usually after Telophase the cell will also divide its cytoplasm and pinch off into two separate but identical daughter cells. Each daughter cell is an exact copy of the parent cell before the DNA was duplicated during Interphase. Completes the cell cycle Memorize steps in order by remembering PMAT or Peas Make Awful Tarts

4 Evidence 13: Do you think this model of the cell cycle is accurate for all cells? Explain your answer. Evidence 14: Use Figure 8 on page 238 to answer the question. Human cells have 46 chromosomes. How many chromosomes should be present during the G2 phase of the cell cycle? How many should be in each daughter cell after cytokinesis? Explain your answer. Evidence 15: Descibe a scenario in the human body in which a stem cell would need to divided into a new stem cell and a specialized cell. Reproduction A process that make new organisms from one or more parent organism 2 ways o Sexual reproduction Involves the joining of two specialized cells called gametes (egg and sperm), one from each parent

5 Offspring are genetically unique and have a mixture of genes from each parent o Asexual reproduction Creation of an offspring from a single parent and does not combining of gametes Offspring are genetically identical to each other and the parent Types of asexual reproduction 1. Spores - Some protozoans and many bacteria, plants and fungi reproduce via spores. Spores are structures naturally grown as part of an organism's life cycle and designed for separation from the organism and dispersal via a medium such as air or water. When conditions are correct, the organism will release its spores, which are each then considered entirely separate and autonomous organisms. Given an environment suitable for life, the spores will then develop into fully grown organisms and eventually grow their own spores, repeating the cycle. 2. Fission - Prokaryotes and some protozoa reproduce via binary fission. Fission occurs at the cellular level when a cell's contents are replicated internally and then subjected to division. The cell then forms into two distinct entities and separates itself. Each partial cell then reconstitutes the missing parts of its internal structure. At the end of the process, the single cell has become two new fully developed cells, each with identical genetic properties. 3. Vegetative reproduction - Many plants have evolved specialized genetic features that allow them to reproduce without the aid of seeds or spores. Examples include the prostrate aerial stems of

6 strawberries, the bulbs of tulips, the tubers of potatoes, the shoots of dandelions, and the keikis of orchids. This form of specialization is most common in environments with seasonally harsh conditions; it allows plants to survive and thrive in situations where the traditional seeding process is subject to frequent interruption. 4. Budding - Organisms like proteins, yeast, and some viruses reproduce via budding, a process by which an entirely new organism grows on an existing one. Unlike fission, this is not brought about by the separation of an existing organism into two partial entities. The developing organism begins its life as an entirely separate life form from its "parent", separating into an autonomous entity only when it has fully matured. As the "child" organism proceeds through life, it will produce its own buds. 5. Fragmentation - Segmented worms and many echinoderms such as starfish reproduce asexually via fragmentation. In this process, an organism physically splits and develops new, genetically identical organisms out of each segment. The segments rapidly grow new cells to constitute their muscle fiber and internal structure through mitosis. This split can be either intentional or unintentional on the part of the organism.

7 Sexual reproduction image Advantages of Asexual Reproduction More efficient than sexual reproduction because produce more in shorter timeframes Genetically identical to the parent so if suited to the environment would be helpful All asexually producing organisms can potentially reproduce Disadvantages of Asexual Reproduction Genetically identical to parent so it would respond to environment the same so if conditions changed this would be harmful If population members lack traits that enable them to reproduce the entire population would eventually die out Advantages of Sexual Reproduction Greater diversity so if environmental changes occur more survival of species Disadvantages of Sexual Reproduction Long gestational period Time, energy and resources are great Evidence 16: Make an argument for the following question. If you wanted to grow a food crop for human consumption, which do you think would be best for the plant to use sexual or asexual reproduction?