Chapter 8 - How Cells Replicate
8.5 will not be tested
- The fusion of 2 gametes create a single fertilized zygote as the
beginning of an organism’s life cycle.
- The cell must go through several thousand rounds of cell division
to produce the large population of cells needed to construct the
body of a multicellular organism
- Throughout this process of cell division the genetic material
must be replicated, condensed and portioned into daughter
cells. This type of cell division is called MITOSIS.
- For sexually reproducing organisms, the gametes mentioned
above are created in gonads by a specialized type of cell division
that must reduce the amount of genetic material by half – This is
- Our body (Somatic cells) are diploid, our gametes are haploid
- Know Fig 8.5 and Fig 8.13 It is essential to understand
meiosis and mitosis before working on inheritance
- Humans inherit 23 chromosomes from each parent so that we
end up with 2 copies of each. Ie. We have 23 pairs of
- Whenever a cell needs to divide it replicates all of the
chromosomes and then splits them down the middle giving one of
each to each of the 2 daughter cells – daughter cells are
identical to the mother cell
- Cells that need to produce gametes replicate all of the
chromosomes and split them, but the split is different this time
- Instead of splitting each replicated chromosome – Meiosis begins
by splitting the members of each pair into daughter cells
- The reduces the number of chromosomes
- A second division splits the replicated chromosomes down the
middle and results in gametes having only half the number of
chromosomes as the original gonad cell
1 8.2 Multiplication by Division pg. 133
Asexual Reproduction - mode by which offspring arise from a
single parent only
Meiosis – nuclear division process that halves the chromosome
number. Basis of sexual reproduction
Mitosis – nuclear division mechanism that maintains the
chromosome number. Basis of body growth, tissue repair and
replacement in multi celled eukaryotes; also asexual reproduction
in some plants, animals, fungi and protists.
Sexual reproduction – reproductive mode by which offspring
arise from two parents and inherit genes from both.
1. A cell reproduces by dividing; nucleus first, then cytoplasm.
2. Each descendant cell receives a complete set of
chromosomes and some cytoplasm
3. Nuclear division mechanisms of mitosis and meiosis partition
chromosomes of a parent cell into new nuclei.
4. Mitosis is the basis of growth, cell replacement and tissue
repair in multi celled species and asexual reproduction in
5. Meiosis is the basis of sexual reproduction in eukaryotes
Take Home Message
1. When a cell divides, each descendant cell receives a set of
chromosomes and some cytoplasm. In eukaryotic cells, the
nucleus divides first , then cytoplasm
2. Mitosis is a nuclear division mechanism that maintains the
chromosome number. It is the basis of body size increases, cell
replacements, and tissue repair in multi celled eukaryotes; and
asexual reproduction in single celled and some multi celled
3. Meiosis, a nuclear division mechanism that halves the
chromosome number is the basis of sexual reproduction in
2 8.3 Mitosis and the Cell Cycle pg. 134
cell cycle – A series of events from the time a cell forms until its
homologous chromosomes paired chromosomes with the same
length, shape and set of genes
interphase – in eukaryotic cell cycle, the interval between mitotic
division when a cell grows, roughly doubles the number it its
cytoplasmic components and replicates its DNA
anaphase- stage of mitosis during which sister chromatids separate
and move towards opposite sides of the cell
metaphase– stage of mitosis at which all chromosomes are aligned in
the middle of the cell
prophase – stage of mitosis during which chromosomes condense and
become attached to a newly forming spindle
spindle – apparatus that moves chromosomes during nuclear division;
consists of dynamically assembled and disassembled microtubules
telophase – stage of mitosis during which chromosomes arrive at
opposite ends of the cell and de condense, and two new nuclei form.
3 1. A cell cycle includes all the stages through which a eukaryotic
cell passes during its lifetime; it starts when a new cell forms, and
ends when the cell reproduces.
2. Most of a cell’s activities, including DNA replication of its
homologous chromosomes, occur during interphase
3. Mitosis maintains the chromosome number
4. During prophase, the duplicated chromosomes condense.
Microtubules form a spindle, and the nuclear envelope breaks up.
Spindle microtubules attach to the chromosomes at the
5. At metaphase, all of the chromosomes are aligned in the middle
of the cell.
6. During anaphase, the sister chromatids of each chromosome
detach and move toward opposite sides of the cell
7. During telophase, a nuclear envelope forms around the two
clusters of chromosomes. Two new nuclei, each with the parental
chromosome number are the result.
Take Home Message
What happens during the cell cycle?
1. A cell’s life passes through a series of stages that include
interphase, mitosis, and cytoplasmic div