Download The Cell Cycle

Chapter 8 and 9
Lesson 1- Chromosomes
Lesson 2- Cell Cycle
Lesson 3-Mitosis
Lesson 4-Meiosis
Chromosomes
Chromosomes
Structures made of DNA and
associated proteins on which genes
are located.
Sets of Chromosomes
 Diploid-a cell that contains two
sets of chromosomes. (2n)
 Haploid- a cell that contains one
set of chromosomes. (n)
 The number of chromosomes in
cells is constant within a species.
Each human cell normally has
two pairs of 23 different
chromosomes for a total of 46
chromosomes.
The 23 pairs of chromosomes differ in size,
shape, and genetic content.
Each pair consists of two homologous
chromosomes or homologues (one from each
parent).
Homologous Example
xx
XX
1
2
•Within each homologous pair, the
chromosomes are similar in size,
shape, and genetic content.
However, each pair is different from
the next.
Autosomes
Are chromosomes that are not
directly involved in determining
the sex (gender) of an individual.
Of the 23 pairs of chromosomes,
22 pairs are called autosomes.
Sex (Gender) Chromosomes
 Are chromosomes that are directly
involved in determining the sex (gender) of
an individual.
 Of the 23 pairs of chromosomes, 1
pair is called sex chromosomes.
 Males – XY
 Females - XX
The sex of the offspring is
determined by the male, who can
donate either an X or Y
chromosome.
The presence of all 46
chromosomes is essential for
normal development and
function.
Chromosome Variations
 A genetic disorder is caused by an
abnormality in an individual's DNA.
 Abnormalities can range from a small
mutation in a single gene to the
addition or subtraction of an entire
chromosome or set of chromosomes.
RESULTS:
1. Down’s Syndrome
2. Turner’s Syndrome
3. Huntington’s Disease
4. Sickle Cell Anemia
5. Cystic Fibrosis
And other genetic disorders . .
The Cell Cycle
The Eukaryotic Cell Cycle
The eukaryotic cell cycle consists of
phases of growth, DNA replication,
preparation for cell division, and
division of the nucleus and cytoplasm.
Stages of the Cell Cycle
1.
2.
3.
4.
5.
First Growth (G1) Phase
Synthesis (S) Phase
Second Growth (G2) Phase
Mitosis (M)
Cytokinesis (C)
The Cell Cycle: Interphase
A cell spends (90%) of its time in Interphase
1.
First Growth (G1) Phase: cell grows rapidly
and carries out its routine functions.
–
Cells that are not dividing remain in the G1 phase.
2.
Synthesis (S) Phase: cell’s DNA is copied.
3.
Second Growth (G2 )Phase: preparations
are made for the nucleus to divide.
Final Stages
Mitosis:
process during cell
division in which
the nucleus of a
cell is divided
into two nuclei.
Cytokinesis:
process during cell
division in which
the cytoplasm
divides.
Importance of Mitosis and Cytokinesis
Mitosis and Cytokinesis produce new cells that
are identical to the original cells and allow
organisms to grow, replace damaged
tissues, and, in some organisms, reproduce
asexually.
 How
do cells
know when to
divide?
 How
is the
cell cycle
controlled?
Check Points

Cells have check points that control the
phases of the cell cycle.

At each checkpoint, feedback signals from
the cell can trigger the next phase of the cell
cycle.
Cell Cycle Review
1.
2.
3.
4.
5.
6.
7.
Define cell cycle.
List the 5 phases of the cell cycle.
List the 3 phases of the cell cycle.
What phases make up Interphase?
How much time does a cell spend in Interphase?
What regulates the cell cycle?
Do all cells go through all stages of the cell cycle?
Mitosis
Mitosis
•Process in which the nucleus
of the cell divides and
maintains the parental
chromosome number for
daughter cells.
Stages of Mitosis
•PROPHASE
•METAPHASE
•ANAPHASE
•TELEPHASE
P
M
A
T
Prophase
Chromosomes coil up and
become visible.
Nuclear envelope dissolves and
a spindle forms
Metaphase
•Chromosomes move to the
center of the cell and line up
along the equator (middle).
•Spindle fibers link the
chromosomes to opposite
poles.
Anaphase
• Centromeres divide
(split)
• Chromatids are pulled
away to opposite poles
of the cell
Telophase
Nuclear envelopes form
around the chromosomes
at each pole.
Two new cells are visible.
Cytokinesis
 During
cytokinesis, the cytoplasm
of the cell membrane grows to
enclose each cell, forming two
separate cells as a result.
ASEXUAL
AND
SEXUAL REPRODUCTION
REPRODUCTION
the process of producing offspring.
Types:
Asexual Reproduction
Sexual Reproduction
SEXUAL REPRODUCTION
• Definition: reproduction in which gametes from
opposite sexes or mating types unite to form a
zygote (fertilized egg).
• Occurs in eukaryotic organisms.
• Two parents each form haploid reproductive cells.
-sperm cells contain 23 chromosomes (Father)
-egg cells contain 23 chromosomes (Mother)
SEXUAL REPRODUCTION CONTD.
• Both parents contribute genetic material
• The offspring has traits of both parents but are
not exactly like either parent.
ADVANTAGES OF SEXUAL REPRODUCTION
Makes different combinations of
genes among individuals.
Leads to greater genetic diversity.
ASEXUAL REPRODUCTION
• Definition: reproduction that involves
only one parent and results in
genetically identical offspring.
• Occurs in Prokaryotes and some
eukaryotes.
• Parent passes copies of all of its genes
to each of its offspring
ASEXUAL REPRODUCTION CONTD.
• There is no fusion of haploid cells
• = clone (an organism that is
genetically identical to its parent)
TYPES OF ASEXUAL REPRODUCTION
1. Binary fission - reproduction in which the
parent separates into one or more
individuals of equal size.
1. Fragmentation -reproduction in which the
body breaks into several pieces.
1. Budding - reproduction in which new
individuals split off from existing ones.
ASEXUAL REPRODUCTION
Advantages
Simple
Allows organisms
to reproduce rapidly
Organisms do not
need a mate
Disadvantages
DNA is identical
to that of the parent
Organism may not
be able to adapt to
a new environment
Let’s Review
1. Define reproduction
2. Some organisms have ______ parents, while others
have ________.
3. Distinguish between asexual reproduction and
sexual reproduction.
4. An individual produced by asexual reproduction is a
_____________.
5. List the types of asexual reproduction.
6. List the disadvantages/advantages of asexual
reproduction.
Meiosis
 A form of nuclear division that creates four haploid
cells from one diploid cell.
 Meiosis reduces the chromosome number and
creates genetic diversity.
 Involves two rounds of cell division-meiosis I and
meiosis II.
Points to Remember
Homologous Chromosomes
 Are two separate
chromosomes
 One comes from the
mother AND one comes
from the father.
 Very similar in size, shape,
and genetic content
 divided in meiosis I.
Sister Chromatids
 Half of a duplicated
chromosome
 Two chromatids together
joined at the centromere
 divided in meiosis II.
Meiosis


Meiosis – Prophase I
 Nuclear membrane breaks down
 Centrosomes and centrioles move
to opposite sides of the cell
 Spindle fibers start to assemble
 Chromosomes condense and
homologous chromosomes pair up.
Meiosis – Metaphase I
 Homologous chromosome pairs
are randomly lined up along the
middle of the cell
 This arrangement mixes up the
chromosomal combinations and
helps create and maintain genetic
diversity.
Meiosis – Anaphase I
Paired homologous chromosomes
separate and move to opposite
sides of the cell
sister chromatids are still
connected.
Meiosis – Telophase I
Chromosomes are in two groups at
opposite sides of the cell.
Cell divides into two haploid
cells.
Meiosis – Prophase II
 Nuclear membrane breaks down
 Centrosomes and centrioles move to
opposite sides of the cell
 Spindle fibers assemble
Meiosis – Metaphase II
 Spindle fibers align the
chromosomes along the cell’s
equator.
Meiosis – Anaphase II
 The sister chromatids are pulled
apart from each other and move to
opposite sides of the cell.
Meiosis – Telophase II
 Nuclear membrane forms around each set of
chromosomes at opposite ends of the cell
 Spindle fibers break apart
Meiosis -- Cytokinesis
 Cytoplasm and organelles finish
replicating and the cell divides into
two.
 Cell membrane forms between the
new cells.
 Four haploid cells are formed.
Mitosis Overview
Meiosis Overview