Chromosomes+HW4+MC

pp.378-379 Chromosomes and the Cell Cycle 1. What is interphase and what are the three stages of interphase. Describe them in detail. -Interphase is a time when the organelles carry on their usual functions. The cells get ready to divide. It grows larger, the number of organelles doubles, and the amount of chromatin doubles as DNA synthesis occurs. It lasts for about 20 hours, which is 90% of the cell cycle. The 1st stage is G one stage. Here a cell doubles its organelles, and it accumulates the materials needed for DNA synthesis. Various proteins are needed to change chromatin into chromosomes that are visible under the microscope when stained. A chromosome contains both proteins called histones and DNA. The second stage is the S stage. Here DNA replication occurs; a copy of DNA in a cell. Because DNA replication occurs, each chromosome consist of two identical DNA double helix molecules. These molecules occur in the strands called sister chromatids. Another way of expressing these events is to say that DNA replication has resulted in duplicated chromosomes. The 3rd stage is the G two stage. Here the cell synthesizes the proteins needed for cell division, such as the protein found in microtubules. The role of microtubules in cell division is described in a later section. 2. Define Mitosis and Cytokinesis and Apoptosis. - Mitosis is a type of nuclear division. It’s called duplication division because each new nucleus contains the same number and kind of chromosomes as the former cell. Cytokinesis is the division of the cytoplasm. Apoptosis is programmed cell death, occurring to do away with any cells that are dividing when they shouldn’t. 3.Insert a picture of the "cell cycle". Label it as :The cell cycle

4. Insert a picture of a human chromosome "karyotype". Label it as karyotype and define karyotype. -A karotype is something that tells us a lot about a body cell. 5. Why would it be important to obtain fetal chromosomes? It would be important to obtain fetal chromosomes for karyotyping, or to see if a syndrome or syndromes have occurred together. 6. Describe the two ways to obtain fetal chromosomes. One way is CVS. It’s usually performed from the eighth to the twelfth week of pregnancy when the doctor inserts a long, thin tube through the vagina into the uterus. It’s placed in between the uterine lining and the chorionic villi. Fetal cells are obtained by suction. Another way is by amniocentesis which is usually performed from the fifteenth to the seventeenth week of pregnancy. A long needle is passed through the abdominal wall to withdraw a small amount of amniotic fluid, along with a few fetal cells. 7.Insert a picture of a drawing of aminiocentesis. Label it as amniocentesis.

8. Describe the structure of a chromosome before duplication and after duplication. Before duplication of a chromosome, chromatin in the nucleus becomes highly condensed and the chromosomes are visible, but after duplication of a chromosome, it composes of two identical parts, called sister chromatids, held together at a centrosome. 9. What does the cell use to pull the duplicated chromosomes apart? Before mitosis begins, the centrosome and the centrioles duplicate; during mitosis, the separate, and the mitotic spindle, composed of microtubules, forms between them. 10. Describe the important parts of each phase of mitosis: Prophase, Metaphase, Anaphase, and Telophase. There’s earlt prophase and prophase. During early prophase centrosomes have duplicated. Chromatin is condensing into chromosome, and the nuclear envelope is fragmenting. During Prophase, nucleolus has disappeared, and duplicated chromosomes are visible. Centrosomes begin moving apart, and the spindle is in process of forming. During early metophase each chromatid is attached to a spindle of fiber. Some spindle fibers stretch form each spindle pole and overlap. During metaphase centrosomes of duplicated chromosomes are aligned at the equator. Spindle fibers attached to the sister chromatids come from opposite spindle poles. During anaphase, sister chromatids part and become daughter chromosomes that move toward the spindle poles. During telophase Daughter cells are forming as nuclear envelopes and nucleoli reappear. Chromosomes will become indistinct chromatin. 11. How is the cytoplasm divided between the daughter cells following mitosis? It’s divided by a process called cytokinesis. Cytokineses is the division of the cytoplasm and organelles. In human cell, a alight indentation called a cleavage furrow passes around the circumference of the cell. Actin filaments form a contractile ring, and as the ring gets smaller and smaller, the cleavage furrow pinches the cell in half. Each cell becomes enclosed by its own place and membrane. 12. When do human body cells go through mitosis normally? Body cells go through mitosis normally when we grow. 13. What is a result of mitosis that is not in control? Give an example of what can occur. A benign tumor or a cancerous tumor develops when the cell cycle control system is not functioning properly. A benign tumor is confined to a particular location, such as Nick’s keloid. A cancerous tumor is not confined. Cancer cells have a tendency to leave the original tumor by way of the lymphatic vessels and start mnew tumors in other parts of the body. 14. Insert a picture that includes each of the phases of mitosis in real cell photographs. Make sure the phases are labeled. 15. Define gamete, haploid chromosome number, diploid chromosome number. You may need to look these up. A gamete is a cell that fuses with another gamete during fertilization in organisms that reproduce sexually. A haploid chromosome number is the number of chromosomes in an egg or sperm cell, half the diploid number. The diploid chromosome complement of a species, designated 2n, consists of the combined haploid chromosome sets, each designated 1n, contributed by the male and female parents at fertilization. 16. Which cells of your body have a diploid number of chromosomes? The zygote has only he diploid number of chromosomes. 17. Which process makes cells with a diploid number of chromosomes? Meiosis. 18. What is the purpose of meiosis? (see page 389). The purpose is to produce or the production of the sperm and egg, and to keep the chromosome number constant from generation to generation. 19. Which cells of your body have a haploid number of chromosomes? The gamete. 20. Which process uses meiosis: sexual or asexual reproduction? Why? Asexual reproduction because one parent has produced identical offspring. Humans and other organisms practice sexual production that includes meiosis because it results in genetic recombination. 21. Which takes less time: sexual or asexual reproduction? Why? Asexual takes less time because binary function is a quick and easy way to asexually reproduce many organisms in a short period of time. 22. Why is sexual reproduction more complicated then asexual reproduction? Because more environments are subject to change, and sexual production generates the diversity needed so that at least a few will be suited to new and different environmental circumstances. 23. How do the benefits of sexual reproduction outweigh the costs? It takes energy to find a mate, carry out a courtship and produce eggs or sperm that may never be used or reproductive purposes.