Download Chromosomes and Cell Reproduction Human Reproduction

Cell Reproduction
Chromosome Structure Review
Except for the gametes, humans have 46
chromosomes (23 pairs) in the nucleus of
every cell.
 Chromosomes are long strands of DNA
(genetic code).
 When chromosomes are uncoiled, they are
called chromatin.
 When chromosomes are coiled, they look
like a “x”.

Chromosome Structure Review
ChromatidsEach half of a
chromosome
Each chromatid
is a double helix
(twisted ladder)
Centromereholds 2 chromatids
together
Cells with different numbers of
chromosomes
Diploid (somatic cell) – A cell consisting of
homologous chromosomes . In humans, this
cell has 46 chromosomes. One chromosome
of a pair came from the mother and one from
the father. All cells in the human body are
diploid except sex cells.
 Haploid (gamete) – A cell that does not
contain chromosome pairs. The sperm and
egg are haploid and, in humans, have 23
chromosomes.

Chromosome Shorthand
n = # of unique chromosomes (haploid)
 2n = # of chromosomes in pairs (diploid)

n=4 Haploid cell
X
x
X
x
2n=8 Diploid cell
XX
xx
xx
XX
Homologous
Pair
Cell Cycle- Series of events for cells
Cytokinesis

Interphase is the time
between cell division. This
is when the cell grows and
replication occurs
(chromatids are copied).
During interphase, DNA is
uncoiled (chromatin).

Mitosis/Meiosis is the
division of the cell’s
nucleus (chromosomes).

Cytokinesis is division of
the cell’s cytoplasm and
membrane. This is when
the cell physically splits in
half.
Interphase
Mitosis or
Meiosis
MITOSIS

Mitosis results in new cells with genetic material
identical to that of the original cell. This process
is the reason for human growth.
 Mitosis occurs in all cells of the body except the
sex cells (egg and sperm cells). Sex cells
undergo a different process called meiosis.
 Mitosis has 4 phases: Prophase, Metaphase,
Anaphase and Telophase.
PROPHASE
DNA supercoils (goes
from chromatin to
chromosomes)
 Nuclear membrane
breaks down
 Nucleolus breaks
down
 Mitotic spindle forms
from the centrosomes
(containing 2
centrioles)

METAPHASE
Chromosomes line
up in single file at
the center of the
cell.
 The chromosomes
(at the centromere)
are held in place by
the mitotic spindle.

ANAPHASE

The chromatids of
each chromosome
separate and move
toward opposite
poles of the cell.

The spindle pulls the
chromatids apart at
their centromere.
TELOPHASE
(opposite of Prophase)
Mitotic spindle breaks
down
 Chromosomes uncoil
(become chromatin)
 Nuclear envelopes
reform
 Nucleolus reappears
within each envelope

CYTOKINESIS
Cytokinesis occurs differently in animal
and plant cells.
 In animal cells, the cell membrane pinches
in until it eventually splits the cell into
two.
 This pinching in is called a cleavage
furrow.

CYTOKINESIS
In plant cells, cytokinesis occurs when a
cell plate forms and splits the cell into
two.
 The cell plate starts to form in the center
and works its way outward until it reaches
the cell wall.

Mitosis and Cytokiinesis Practice

Each student kit needs:
– one 8 foot orange string cut in ½
– One 5 foot black string cut in ½
– 1 clear spoon and fork
– 1 white spoon and fork
– 2 pom-poms
– 2 paper clips
– 8 coffee stirrers
What is the cell cycle phase?
(IPMATC)
What is the cell cycle phase?
(IPMATC)
What is the cell cycle phase?
(IPMATC)
What is the cell cycle phase?
(IPMATC)
What is the cell cycle phase?
(IPMATC)
What is the cell cycle phase?
(IPMATC)
Meiosis
A type of cell division in which the
chromosome # is reduced by half to produce
haploid cells.
 This produces gametes (sex cells).
 Meiosis has the same phases as mitosis;
however, it goes through 2 rounds of these
phases. The phases of meiosis are Prophase
I/II, Metaphase I/II, Anaphase I/II and
Telophase I/II.

PROPHASE I
Nuclear membrane breaks down
 Nucleolus breaks down
 Mitotic spindle forms from the centrosomes
 Chromatin coils to become chromosomes
 Homologous chromosomes position
themselves next to each other- This is called
synapsis.
 Crossing over occurs- This is when
homologous chromosomes “swap” pieces of
DNA with each other.

METAPHASE I

Homologous pairs line up along the
midline of the cell.
ANAPHASE I

Homologous chromosomes move away
from each other toward opposite poles of
the cell.
TELOPHASE I
Nuclear membrane forms around each set
of chromosomes
 Spindle breaks down
 Chromosomes do not uncoil and
nucleoluses do not form because there is
a second round of nuclear division.
 This is followed by Cytokinesis I which
produces 2 haploid cells.

PROPHASE II
Nuclear membrane breaks down
 Spindle forms

METAPHASE II

Chromosomes line up in single file along
the midline of the cell.
ANAPHASE II

Chromatids of chromosomes separate and
move to opposite poles of the cell.
TELOPHASE II
Chromosomes uncoil to become
chromatin.
 Nuclear membranes form around each set
of chromosomes
 Nucleoluses form in each nuclear
membrane.
 Spindle breaks down.
 This is followed by Cytokinesis II which
produces 4 haploid cells.

Differences between mitosis and
meiosis

Mitosis
– Metaphasechromosomes are in
single file
– 2 product cells
(diploid)
– Somatic cells (nonsex) produced
– 4 phases (PMAT)

Meiosis
– Metaphase I
chromosomes are aligned
as pairs
– 4 product cells (haploid)
– Sex cells (gametes)
produced
– Synapsis and crossing
over occurs during
Prophase I
– 8 phases (PMAT 1 and 2)
What if meiosis yields sex cells
with < or >23 chromosomes?
Down Syndrome
 Turner Syndrome
 Klinefelter Syndrome
