Chapter 8-The Cellular Basis of Reproduction and Inheritance
8.3- Prokaryotes reproduce by binary fission
Objectives: 1) Describe the events of binary fission
I. Cell Division in Prokaryotes
A. Binary fission
1. Cell division in prokaryotic cells resulting in 2 cells
2. The Steps
a. Chromosome make a copy of itself
1. A single, circular strand of DNA
b. Cell grows to approx. twice the
cells original size
c. Cell wall forms between the 2
chromosomes
d. Cell divides into 2 identical cells
8.4-The large, complex chromosome of eukaryotes duplicate with each cell division
Objectives: 1) Define chromatin
2) Describe the structure of a chromosome
3) Distinguish the difference between sister chromatids and
chromosomes
I. DNA Structure
A. The form in which info in the cell is contained
B. The cells alphabet
C. Comprised of nucleic acids
D. A double helix
E. Each strand contains thousands of genes
1. Each gene contains a specific code which is
responsible for a different trait
II. Chromatin
A. The state in which DNA is normally found in nondividing cells
1. DNA is too long to fit into the cell
a. Each chromosome contains approx. 5 cm of DNA when
uncoiled
B. DNA coiled around proteins called histones
C. When cell division is initiated, this chromatin coils & condenses into
microscopic chromosomes.
III. A chromosome
A. Strands of DNA wrapped around proteins (chromatin) and tightly
condensed
B. In most cells, chromosomes are only visible during cell division
C. Most other times, they are uncoiled
8.5-The cell cycle multiplies cells
Objectives: 1) Define the cell cycle
I. Cell Cycle
A. Repeating set of events that make up the life of a cell
1. The sequence of division and growth of a cell’s life cycle
a. Interphase
1. Subdivided into G1, S, G2
b. Mitotic phase (M phase)
1. Subdivided into mitosis and cytokinesis
8.6-Cell division is a continuum of dynamic changes
Objectives: 1) Describe each phase of interphase
2) Describe each phase of mitotic phase
3) Summarize the phases of interphase & mitosis
I. Interphase
A. The growth phaseCells spend most of their lifetime in this
phase
B. G1 phase
1. Offspring cells grow to mature size
C. S phase
1. Cell’s DNA is copied
D. G2 phase
1. Cell prepares for cell division
II. Mitotic Phase (M phase)
A. Nuclear division occurs
1. The process by which 2 daughter cells are formed
a. Each containing a complete set of chromosomes
B. Phases of mitosis
1. Prophase/Prometaphase: the 1st phase
a. Chromatin coils into visible chromosomes
1. Remember in S phase the DNA was copied
2. Sister chromatids stay connected by the centromere
b. Nuclear membrane disappears
c. Centrioles & Spindle fibers form
1. Spindle fibers are a network of protein fibers
d. Spindle fibers attach to centromeres
2. Metaphase: the 2nd phase
1. The chromosomes line up in center of cell
3. Anaphase: the 3rd phase
1. Sister chromatids separate
a. Spindle fibers pull each chromosome to opposite sides of cell
d. Telophase: the 4th phase
1. Each side of cell now has a complete set of chromosomes
2. Chromosomes begin to unwind
3. Spindle fibers break down
4. Nuclear envelope forms around each set of chromosomes
5. A new plasma membrane begins to form between the two
nuclei
C. Cytokinesis
1. Actual cell division
2. Cytoplasm is pinched in half
a. Cleavage furrow
1. Area of the cell membrane that pinches in
b. Forms 2 new cells
3. Each cell contains identical DNA
4. Cell enters growth phase
Cleavage Furrow
8.7- Cytokinesis differs for plant and animal cells
Objectives: 1) Describe the difference between plant and animal cell cytokineses
I. Animal cells
A. Cleavage furrow develops between 2 new cells
II. Plant cells
A. Cell plate forms between 2 new cells
8.10-Growing out of control, cancer cells produce malignant tumors
II. What happens when the cell cycle is not controlled?
A. A tumor develops
1. A mass off cells that results from
uncontrolled growth
2. Benign tumor
a. A tumor that remains in the region in
which it was originally formed
b. Usually harmless
B. Cancer develops
1. A tumor that does not remain in the region in which it was originally
formed
a. Malignant tumor
2. Uncontrolled cell division
3. Most prevalent types of cancer in U.S.
a. Lung
b. Prostate
c. Colon
d. Breast
8.12-Chromosomes are matched in homologous pairs
I. Human cells & chromosomes
A. Somatic cells
1. Body cells
2. Composed of 46 chromosomes
a. Remember: Chromosomes are composed of 2 sister chromatids
b. Each chromosome has a twin chromosome that is identical in length and
centromere position
1. 23 pairs of chromosomes
a. Homologous chromosomes (or homologs)
2. The exception
a. Sex chromosomes
1. Female XX, Male XY
8.13-Gametes have a single set of chromosomes
I. Somatic cells
A. 46 chromosomes or 23 pairs
B. Diploid
1. Cells with 2 homologous sets of chromosomes
2. Represented as 2n
a. Humans: Diploid number is 46 - 2n=46
1. In order to be human you must have 46 chromosomes
II. Sex cells (gametes)
A. Reproduction
1. In order to reproduce sexually the chromosome number in sex cells must be
reduced to half
a. A single set of chromosomes
b. Haploid cell
1. Humans: Haploid number is 23 – n=23
2. Dad gives 23 chromosomes/mom gives 23 chromosomes = 46 chromosomes
a. Dad’s gamete (sperm/haploid) fertilizes mom’s gamete (egg/haploid) creating
a diploid zygote
B. How do we get from a diploid cell to a haploid cell?
1. Meiosis
8.14-Meiosis reduces the chromosome number from diploid to haploid
Objectives: 1) Describe each phase of meiosis
2) Summarize the phases of meiosis
3) Be able to describe the purpose and importance of meiosis
I. Stages of meiosis
A. Defined
1. Process of nuclear division that reduces the number of chromosomes
in new cells to half the # of diploid chromosomes
2. Cells go through interphase
B. Meiosis I
1. 4 phases
a. Prophase I
1. Chromatin coils into chromosomes
2. Spindle fibers appear
3. Nuclear membrane disappears
4. Homologous chromosomes pair up
a. Called synapsis
b. Does not happen in mitosis
c. Each pair is called a tetrad
d. Chromatids line up so corresponding genes line up next to each
other
e. Crossing-over
1. Portions of broken chromatids attach to adjacent chromatids
on homologous chromosomes
2. Results in genetic recombination
a. Producing a new mixture of genetic material
b. Metaphase I
1. Tetrads randomly line up along equator of cell
2. Spindle fibers attach to centromeres
3. Spindle fibers from opposite poles attach to different centromeres
w/in tetrad
c. Anaphase I
1. Each homologous chromosome moves to opposite ends of cell
d. Telophase I
1. Spindle fibers disappear
C. Cytokinesis I
C. Meiosis II
1. Same as Mitosis w/ the exception of no nuclear envelope break down
8.15- Mitosis and meiosis have important similarities and differences
Objectives: 1) Be able to describe the difference between mitosis and meiosis