BIO 181: Unity of Life
Study Guide for Chapter 9
1. Which of the following is true of mitosis?
A. The chromosome number in the resulting cells is halved.
B. DNA replication is completed in prophase
C. Crossing over occurs during prophase
D. 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.
2. Which of the following is true of meiosis?
A. the chromosome number in the resulting cells is halved
B. DNA replication occurs after the beginning of meiosis
C. The homologs do not pair during prophase I
D. The chromosome number of the resulting cells is the same as that of the
parent
A. 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.
3. Which of the following is true of chromatids?
A. They are replicated chromosomes still joined together at the centromere
B. They are identical in mitotic chromosomes
C. They are identical in meiotic chromosomes
D. 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.
4. Programmed cell death (Apoptosis)
A. Ocurs in cells that have been deprived of essential nutrients.
B. Occurs only in cells that have damaged DNA
C. Is a natural process during development
D. 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.
5. 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.
6. 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.
7. Compare meiosis and mitosis
See notes and text. Consider location of each process and results.
8. 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
the cell.
9. 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.
10. 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.
11. What is a karyotype?
Arrangement of chromosomes from largest to smallest. Both banding patterns and
position of the centromeres are used.
12. When does crossing over occur?
Prophase I of meiosis
13. 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
14. 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