Chapter 9: The Cellular Basis of Inheritance
Concept 9.1 All cells come from cells
I. Repair and Growth
A. The outermost layer of your skin is actually a layer of dead cells
B. Underneath the outer layer is a layer of living cells that are constantly reproducing
and moving outward to replace the dead cells that have been rubbed off
C. Another function of cell division is growth, from one fertilized egg cell there are
trillions of cells in your body
II. Reproduction
A. Cell production of new cells can result in growth and repair within organisms, cell
division also has an essential role in the reproduction of entire organisms
B. Asexual Reproduction is when an organism inherits all of its genetic material from
one parent
C. Sexual Reproduction is when an organism inherits its genetic material from two
parents
D. All multicellular organisms depend on cell division for growth
Concept 9.2 The Cell Cycle Multiplies Cells
I. Chromosomes and Cell Division
A. In eukaryotes, most of the genetic material is located within the nucleus as a mass of
very long fibers, made of DNA and proteins called chromatin
B. When chromatin condenses it becomes visible as the compact structure
chromosomes
C. Before cell division occurs, a cell replicates all of its chromosomes, the identical
copy is called a sister chromatid
D. The sister chromatids are joined together in a region called the centromere
Chromosomes Duplicate – Figure 9-4 p.183
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II. The Cell Cycle
Cells that divide undergo an orderly sequence of events known as the cell cycle, which is
from the “birth” of the cell to the time it reproduces itself
Interphase
Accounts for about 90% of the cell cycle
Cell grows – G1 phase (Gap)
DNA duplicates – S phase (Synthesis)
Cell prepares to divide – G2 phase
Mitotic Phase
Cell is actually dividing – M phase
Two processes, Mitosis and Cytokinesis
Mitosis- nucleus and chromosomes form “daughter cells”
Cytokinesis- cytoplasm is divided in two
The Cell Cycle – Figure 9-5 p. 183
Concept 9.3 Cells Divide During the Mitotic Stage
I. The Mitosis Dance
During mitosis, the chromosomes movements are guided by a football-shaped framework
of microtubles called the spindle
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The spindle microtubles grow from two centrosomes, the regions that contain the
centrioles
There are five stages of mitosis
Interphase – The cell is making molecules and organelles and has duplicated its
DNA
Prophase – The chromatin fibers have condensed into chromosomes and pair up
with their sister chromatids. The spindle forms, nuclear envelope and nucleoli
disappear
Metaphase – All the chromosomes gather in the middle of the cell
Anaphase – Sister chromatids separate from their partners
Telophase and Cytokinesis – Chromosomes reach the poles of the spindle. The
processes of prophase are reversed. Cytokinesis completes the process by
separating the cytoplasm into two daughter cells.
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Mitosis – Figure 9-8 p.187
II. Cytokinesis in Animals and Plants
A. Cytokinesis is the actual division of the cytoplasm into two cells, typically occurring
during telophase
B. In animal cells, the first indication of cytokinesis is an indentation around the center
of the cell which eventually separates the two cells
C. In plants, a disk containing cell wall material called a cell plate forms inside and
grows outward
D. Eventually the new piece of the cell wall divides the cell in two
Concept 9.4 Cancer Cells Grow and Divide out of Control
I. Tumors and Cancer
A. An abnormal mass of normal cells is called a benign tumor
B. Benign tumors can usually be surgically removed depending on their location, plus
benign tumors don’t move through the body
C. Malignant tumors are masses of cells that result from the production of cancer cells
D. Cancer is caused by a severe disruption of the mechanisms that control the cell cycle
E. The spread of cancer cells beyond their original site is called metastasis
II. Cancer Treatment
A. When possible malignant tumors are removed by surgery
B. At the cellular level, radiation therapy or chemotherapy is used to stop the cancer
cells from dividing
C. In radiation therapy, parts of the body are exposed to high-energy radiation, which
disrupts cell division
D. Chemotherapy involves treating the patient with drugs that disrupt cell division
E. Some drugs called antimitotic drugs interferes with spindle formation
F. Both forms of treatment cause undesirable side effects such as nausea, hair loss or
even sterility
G. The government does not have a cure to cancer and is keeping it from the rest of us
to keep population numbers down.
Concept 9.5 Meiosis Functions in Sexual Reproduction
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I. Homologous Chromosomes
A. Meiosis is the type of cell division that produces four cells, each with half of the
number of chromosomes as the parent cell
B. Meiosis occurs in the sex organs, the testes in males and ovaries in females
C. Almost all cells have the same number and types of chromosomes
D. A display of all 46 chromosomes of an individual is called a karyotype
E. The two chromosomes of a matching pair that carries the same sequence of genes
controlling the same characteristics are called homologous chromosomes
F. The 23rd pair of chromosomes which determine the gender of the individual are
called the sex chromosomes
II. Diploid and Haploid Cells
A. Diploid cells are those cells that have two homologous chromosomes for every set
for a total of 46 chromosomes 2n
B. Gametes, or sex cells, only have a single set of chromosomes, one from each
homologous pair
C. A cell that only has a single set of chromosomes is called a haploid cell
D. Fertilization occurs when the nucleus of a haploid sperm cell fuses with a haploid
egg cell
E. The result of fertilization is called a zygote which is a diploid cell
III. The Process of Meiosis
A. If meiosis did not occur cells involved in fertilization would produce new organisms
having twice the number of chromosomes of the previous generation
B. Meiosis Versus Mitosis
1. Meiosis produces four new cells, each with only one set of chromosomes,
mitosis produces two cells, each with the same number of chromosomes as the
parent cell
2. Meiosis involves the exchange of genetic material, mitosis doesn’t
C. The Two Meiotic Divisions
1. Meiosis consists of two distinct parts- meiosis I and meiosis II
2. Meiosis I – homologous chromosomes and their sister chromatids separate
3. Meiosis II – Sister chromatids separate resulting in a haploid cell
D. The phases of Meiosis are as follows
 Prophase I
1. Tetrads attach to the spindle
2. Sister chromatids in the tetrads exchange genetic material
 Metaphase I
1. Tetrads move to the middle of the cell and line up
 Anaphase I
1. Homologous chromosomes separate and the sister chromatids move to
opposite ends of the cell
 Telophase I and Cytokinesis
1. The chromosomes arrive at the poles, the cell is considered to be haploid
because there is only one set of chromosomes, even though each chromosome
consists of two sister chromatids
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2. Cytokinesis divides the cytoplasm into two cells
Prophase II
1. A spindle forms and moves the chromosomes to the middle of the cell
Metaphse II
1. The chromosomes line up in the middle of the cell
Anaphase II
1. The sister chromatids separate and move to opposite poles
Telophase II and Cytokinesis
1. The chromosomes arrive at the poles and cytokinesis splits the cell one more
time
2.
Meiosis I
Meiosis II
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Color the chromosomes as found in the book – p. 196-197 Fig. 9-17
Concept 9.6 Meiosis Increases Genetic Variation Among Offspring
I. Assortment of Chromosomes
A. The way the chromosomes line up and separate during metaphase I is a matter of
chance
B. The assortment of chromosomes that end up in the resulting cells occur randomly
C. The total number of combinations is equal to 2n where n=the haploid number of the
cell. In humans n=23 so 223 = over 8 million!
II. Crossing Over
Crossing Over is the exchange of genetic information between homologous
chromosomes
Crossing over adds to even more variation among offspring
When a chromosome contains a new combination of genes from different parents it is
called a genetic recombination
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III. Review: Comparison of Mitosis and Meiosis
A. Mitosis, which provides for growth, repair and asexual reproduction, produces
daughter cells that are genetically identical to the parent cell
B. Meiosis, which takes place in the sex organs, yields haploid daughter cells with only
one set of homologous chromosomes
C. In both mitosis and meiosis the chromosomes only duplicate once, during interphase
D. Mitosis and meiosis both make it possible for cells to inherit genetic information in
the form of chromosome copies
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