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General Biology (BSC 1005)
Broward College
The Cellular Basis of Reproduction and Inheritance
I. Introduction
A. Cancer cells
1. start out as normal body cells
2.
3. lose the ability to control the tempo of their own division
4. run amok, causing deadly disease
B. In a healthy body, cell division allows for
1. growth
2.
3. development from an embryo into an adult
C. In sexually reproducing organisms, eggs and sperm result from
1. mitosis
2. meiosis
II. Cell Division and Reproduction
A. 8.1 Cell division plays many important roles in the lives of organisms
1. Organisms reproduce their own kind, a key characteristic of life
2. Cell division
a. is reproduction at the cellular level
b.
c. sorts new sets of chromosomes into the resulting pair of daughter cells
3. Cell division is used
a. for reproduction of single-celled organisms
b.
c. repair and replacement of cells
d. sperm and egg production
4. Living organisms reproduce by two methods
a. Asexual reproduction
i. produces offspring that are identical to the original cell or organism
ii. involves inheritance of all genes from one parent
b. Sexual reproduction
i. produces offspring that are similar to the parents, but show variations in traits
ii. involves inheritance of
B. 8.2 Prokaryotes reproduce by binary fission
1. Prokaryotes (bacteria and archaea) reproduce by binary fission (“dividing in half”)
2. The chromosome of a prokaryote is
a. a singular circular DNA molecule associated with proteins
b. much smaller
3. Binary fission of a prokaryote occurs in three stages
a. duplication of the chromosome and separation of the copies
b. continued elongation of the cell and movement of the DNA copies
c.
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III. The Eukaryotic Cell Cycle and Mitosis
A. 8.3 The large, complex chromosomes of eukaryotes duplicate with each cell division
1. Eukaryotic cells
a. are more complex and larger than prokaryotic cells
b. have more genes
c. store most of their genes
2. Eukaryotic chromosomes are composed of chromatin consisting of
a. one long DNA molecule
b. proteins that help maintain the chromosome structure and
3. To prepare for division, the chromatin becomes
a. highly compact
b. visible with a light microscope
4. Before a eukaryotic cell begins to divide, it duplicates all of its chromosomes,
resulting in
a. two copies called sister chromatids
b. joined together by a narrowed “waist” called the centromere
5. When a cell divides, the sister chromatids
a. separate from each other, now called chromosomes
b.
B. 8.4 The cell cycle multiplies cells
1. The cell cycle is an ordered sequence of events that extends
a. from the time a cell is first formed from a dividing parent cell
b. until its own division
2. The cell cycle consists of two stages, characterized as follows:
a. Interphase:
i. G1—growth, increase in cytoplasm
ii. S—duplication of chromosomes
iii. G2—growth, preparation for division
b. Mitotic phase:
i. Mitosis—division of the nucleus
ii. Cytokinesis—division of cytoplasm
C. 8.5 Cell division is a continuum of dynamic changes
1. Mitosis progresses through a series of stages
a.
b.
c.
d.
e.
2. Cytokinesis often overlaps telophase
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3. A mitotic spindle is
a.
b. composed of microtubules
c. produced by centrosomes, structures in the cytoplasm that
i. organize microtubule arrangement
ii. contain a pair of centrioles in animal cells
4. Interphase
a. The cytoplasmic contents double
b. two centrosomes form
c.
d. nucleoli, sites of ribosome assembly, are visible
5. Prophase
a. In the cytoplasm microtubules begin to emerge from centrosomes, forming the
spindle
b. In the nucleus
i. chromosomes coil and become compact
ii.
6. Prometaphase
a. Spindle microtubules reach chromosomes, where they
i. attach at kinetochores on the centromeres of sister chromatids
ii. move chromosomes to the center of the cell through associated protein
“motors”
b. Other microtubules meet those from the opposite poles
c.
7. Metaphase
a. The mitotic spindle is fully formed
b.
c. Kinetochores of sister chromatids are facing the opposite poles of the spindle
8. Anaphase
a.
b. Daughter chromosomes are moved to opposite poles of the cell as
i. motor proteins move the chromosomes along the spindle microtubules
ii. kinetochore microtubules shorten
c. The cell elongates due to lengthening of nonkinetochore microtubules
9. Telophase
a. The cell continues to elongate
b. The nuclear envelope forms around chromosomes at each pole, establishing daughter
nuclei
c.
d. The spindle disappears
10. During cytokinesis, the cytoplasm is divided into separate cells
11. The process of cytokinesis differs in animal and plant cells
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D. 8.6 Cytokinesis differs for plant and animal cells
1. In animal cells, cytokinesis occurs as
a.
b. the cleavage furrow deepens to separate the contents into two cells
2. In plant cells, cytokinesis occurs as
a. a cell plate forms in the middle, from vesicles containing cell wall material
b. The cell plate grows outward to reach the edges, dividing the contents into two cells
c.
E. 8.7 Anchorage, cell density, and chemical growth factors affect cell division
1. The cells within an organism’s body divide and develop at different rates
2. Cell division is controlled by
a. the presence of essential nutrients
b. growth factors, proteins that stimulate division
c.
d. anchorage dependence, the need for cells to be in contact with a solid surface to divide
F. 8.9 Growing out of control, cancer cells produce malignant tumors
1. Cancer currently claims the lives of 20% of the people in the United States and other
industrialized nations
2. Cancer cells escape controls on the cell cycle
3. Cancer cells
a.
b. spread to other tissues through the circulatory system
c. grow without being inhibited by other cells
4. A tumor is an abnormally growing mass of body cells
a. Benign tumors remain at the original site
b. Malignant tumors spread to other locations,
5. Cancers are named according to the organ or tissue in which they originate
a. Carcinomas arise in
b. Sarcomas arise in supportive and connective tissue
c. Leukemias and lymphomas arise from blood-forming tissues
6. Cancer treatments
a. Localized tumors can be
i. removed surgically and/or
ii. treated with concentrated beams of high-energy radiation
b. Chemotherapy is used for metastatic tumors
G. 8.10 Review: Mitosis provides for growth, cell replacement, and asexual reproduction
1. When the cell cycle operates normally, mitosis produces genetically identical cells for
a.
b.
c.
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IV.
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Meiosis and Crossing Over
A. 8.11 Chromosomes are matched in homologous pairs
1. In humans, somatic cells have
a.
b. one member of each pair from each parent.
2. The human sex chromosomes X and Y differ in size and genetic composition
3. The other 22 pairs of chromosomes are autosomes with the same size and genetic
composition
4. Homologous chromosomes are matched in
a. length
b. centromere position
c.
5. A locus (plural, loci) is the position of a gene
6. Different versions of a gene may be found at the same locus on maternal and paternal
chromosomes
B. 8.12 Gametes have a single set of chromosomes
1. An organism’s life cycle is the sequence of stages leading
a. from the adults of one generation
b. to the adults of the next
2. Humans and many animals and plants are diploid, with body cells that have
a.
b.
3. Meiosis is a process that converts diploid nuclei to haploid nuclei
a. Diploid cells have two homologous sets of chromosomes
b.
c. Meiosis occurs in the sex organs, producing gametes—sperm and eggs
4. Fertilization is the union of sperm and egg
5. The zygote has a diploid chromosome number, one set from each parent
6. All sexual life cycles include an alternation between
a.
b.
7. Producing haploid gametes prevents the chromosome number from doubling in every
generation
C. 8.13 Meiosis reduces the chromosome number from diploid to haploid
1. Meiosis is a type of cell division that produces
2. Two haploid gametes combine in fertilization to restore the diploid state in the zygote
3. Meiosis and mitosis are preceded by the duplication of chromosomes. However,
a. meiosis is followed by
b. mitosis is followed by only one cell division
4. Because in meiosis, one duplication of chromosomes is followed by two divisions, each of
the four daughter cells produced has a haploid set of chromosomes
5. Meiosis I – Prophase I – events occurring in the nucleus
a. Chromosomes coil and become compact
b. Homologous chromosomes
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c. Each pair, with four chromatids, is called a tetrad
d. Nonsister chromatids exchange genetic material by crossing over
6. Meiosis I – Metaphase I – Tetrads align at the cell equator
7. Meiosis I – Anaphase I – Homologous pairs separate and
8. Meiosis I – Telophase I
a. Duplicated chromosomes have reached the poles
b. A nuclear envelope re-forms around chromosomes in some species
c. Each nucleus has the
9. Meiosis II follows meiosis I without chromosome duplication
10. Each of the two haploid products enters meiosis II
11. Meiosis II – Prophase II
a. Chromosomes coil and become compact
b. Nuclear envelope breaks up
12. Meiosis II – Metaphase II – Duplicated chromosomes align at the cell equator
13. Meiosis II – Anaphase II
a. sister chromatids separate
b. chromosomes move
14. Meiosis II – Telophase II
a. Chromosomes have reached the poles of the cell
b. A nuclear envelope forms around each set of chromosomes
c. With cytokinesis,
D. 8.14 Mitosis and meiosis have important similarities and differences
1. Mitosis and meiosis both
a. begin with diploid parent cells
b. have chromosomes duplicated during the previous interphase
2. However, the end products differ
a. Mitosis produces two genetically identical diploid somatic cells
b. Meiosis produces four
E. 8.15 Independent orientation of chromosomes in meiosis and random fertilization lead to varied
offspring
1. Genetic variation in gametes results from
a. independent orientation at metaphase I
b.
2. Independent orientation at metaphase I
a. Each pair of chromosomes
b. There is an equal probability of the maternal or paternal chromosome facing a
given pole
c. The number of combinations for chromosomes packaged into gametes is 2n where
n = haploid number of chromosomes
3. Random fertilization – The combination of each unique sperm with each unique egg
increases genetic variability
F. 8.17 Crossing over further increases genetic variability
1. Genetic recombination is the production of new combinations of genes due to crossing over
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2. Crossing over is an exchange of corresponding segments between separate (non-sister)
chromatids on homologous chromosomes
a. Nonsister chromatids join at a chiasma (plural, chiasmata), the site of attachment and
crossing over
b. Corresponding amounts of genetic material are exchanged
V. Alterations of Chromosome Number and Structure
A. 8.18 A karyotype is a photographic inventory of an individual’s chromosomes
1. A karyotype is an ordered display of magnified images of an individual’s chromosomes
arranged in pairs
2. Karyotypes
a. are often produced from dividing cells arrested at metaphase of mitosis
b. allow for the observation of:
c.
d.
e.
B. 8.19 CONNECTION: An extra copy of chromosome 21 causes Down syndrome
1. Trisomy 21
a. involves the inheritance of three copies of chromosome 21
b. is the most common human chromosome abnormality
2. Trisomy 21, called Down syndrome, produces a characteristic set of symptoms, which
include:
a.
b.
c. short stature
d. heart defects
e. susceptibility to respiratory infections, leukemia, and Alzheimer’s disease
f. shortened life span
3. The incidence increases with the age of the mother
C. 8.20 Accidents during meiosis can alter chromosome number
1. Nondisjunction is the failure of chromosomes or chromatids to separate normally during
meiosis. This can happen during
a. meiosis I, if both members of a homologous pair go to one pole or
b. meiosis II if both sister chromatids go to one pole
2. Fertilization after nondisjunction
D. 8.21 CONNECTION: Abnormal numbers of sex chromosomes do not usually affect
survival
1. Sex chromosome abnormalities tend to be less severe, perhaps because of
a. the small size of the Y chromosome
b. X-chromosome inactivation
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2. Table 8.21 in the textbook lists the most common human sex chromosome abnormalities. In
general,
a. a single Y chromosome is enough to produce “maleness,” even in combination with
several X chromosomes
b. the absence of a Y chromosome yields “femaleness.”
E. 8.23 CONNECTION: Alterations of chromosome structure can cause birth defects and cancer
1. Chromosome breakage can lead to rearrangements that can produce
a. genetic disorders or,
b. if changes occur in somatic cells, cancer
2. These rearrangements may include
a. a deletion, the
b. a duplication, the repeat of a chromosome segment
c. an inversion, the reversal of a chromosome segment
d. a translocation, the attachment of a segment to a nonhomologous chromosome that can be
reciprocal
3. Chronic myelogenous leukemia (CML)
a. is one of the most common leukemias
b. affects cells that give rise to white blood cells (leukocytes)
c. results from part of
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