BIO 181: Unity of Life

Study Guide for Chapter 9

  1. Which of the following is true of mitosis?
  2. The chromosome number in the resulting cells is halved.
  3. DNA replication is completed in prophase
  4. Crossing over occurs during prophase
  5. Two genetically identical daughter cells are formed

D. Mitosis occurs after DNA replication and results in cells that are genetically identical to the parent cell.

  1. Which of the following is true of meiosis?
  2. the chromosome number in the resulting cells is halved
  3. DNA replication occurs after the beginning of meiosis
  4. The homologs do not pair during prophase I
  5. The chromosome number of the resulting cells is the same as that of the parent
  1. Meiosis occurs after one DNA replication, homologous chromosomes pair during prophase I of meiosis, and the resulting cells have half the number of chromosomes as the parent cell.
  1. Which of the following is true of chromatids?
  2. They are replicated chromosomes still joined together at the centromere
  3. They are identical in mitotic chromosomes
  4. They are identical in meiotic chromosomes
  5. A and b

D. Chromatids are highly condensed, newly replicated chromosomes, which will be segregated to the daughter cells. After DNA replication, chromatids are still attached to one another at the centromere. Meiotic sister chromatids are different from one another due to crossing over in prophase I. Mitotic sister chromatids are identical.

  1. Programmed cell death (Apoptosis)
  2. Ocurs in cells that have been deprived of essential nutrients.
  3. Occurs only in cells that have damaged DNA
  4. Is a natural process during development
  5. Is signaled by the initiation of mitosis

C. Programmed cell death occurs during the development of many organisms (for instance, tadpoles lose their tails to become adult frogs). One of the stimuli for programmed cell death is DNA damage, but it is not the only cause of death. Necrosis (cell death that is not programmed) occurs when cells have been deprived of essential nutrients. The initiation of mitosis is part of the cell cycle, in which cells reproduce, and is not a step in programmed cell death.

  1. How do cytokinesis differ in animal and plant cells?

In animal cells cytokinesis results from the interaction of myosin and actin filaments which causes the cell membrane to pinch in and divide the cytoplasm into two cells. In plant cells, a cell plate forms between the newly segregated chromosomes and Golgi vesicle fuse at that site to form new cell membranes. Cell wall components are then secreted between the plasma membranes to complete cytokinesis.

  1. Describe two ways that genetic diversity of organisms is increased during meiosis.

Genetic diversity is increased during crossing over of prophase I of meiosis so that each gamete has chromosomes with different combinations of alleles. During meiosis, each homologous chromosome is randomly segregated to one of the two poles, leading to 223 different combinations of homologous chromosomes per gamete.

  1. Compare meiosis and mitosis

See notes and text. Consider location of each process and results.

  1. What 3 events are unique to meiosis?

Homologous chromosomes, rather than individual chromosomes, line up during metaphase I

Synapsis occurs in prophase I

During anaphase I, sister chromatids do not separate as they do in mitosis. Rather the two sister chromatids of each chromosome remain attached and go the same pole of thecell.

  1. Distinguish among DNA, chromatin, chromosomes, chromatids.

DNA – double helix composed of nucleotides

Chromatin – DNA is thin, and threadlike

Chromosomes – DNA has condensed or supercoiled

Chromatids – half of a double chromosome.

  1. What are the main events in prophase, metaphase, anaphase and telophase?

Prophase – nuclear envelope and nucleolus disappear, centrosome migrates to poles, aster rays and spindle fibers appear. Chromatin supercoils to form chromosomes.

Metaphase – chromosomes line up at the equator (middle) of the cell

Anaphase – chromosomes separate

Telophase - nuclear envelope and nucleolus reappear, centrosome is located outside the nucleolus, aster rays and spindle fibers reappear. Cleavage or beginning of new cell wall is apparent. Chromosomes begin long, and threadlike (chromatin)

11. Distinguish among centrosome, centrioles, centromere, and kinetochore

Centromere holds the two chromatids together

Centrioles are located inside the centrosome; they have no apparent function

Centrosome contains the centrioles; replicate and move to opposite ends (poles) of the cell during prophase

Kinetochore are located outside the centromere. Connect to spindle fibers and aid in separation during anaphase.

  1. What is a karyotype?

Arrangement of chromosomes from largest to smallest. Both banding patterns and position of the centromeres are used.

  1. When does crossing over occur?

Prophase I of meiosis

  1. What causes Down’s, Turners, and Klinefelter’s syndrome?

Nondisjunction – failure of chromosome pairs to separate

What are the distinguishing characteristics of each?

Down’s – trisomy 21, mental retardation, etc.

Turner’s – single X, sterile, short, etc.

Klinefelters – XXY, sterile, tall, etc.

See your notes

  1. Distinguish between haploid and diploid cells.

Haploid cells are gametes that contain 22 autosomes and either X or Y

Diploid cells are body cells that contain 44 autosomes and either XX or XY