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Chromosomes and Cell
Reproduction
Chap. 6
Section 1
Chromosomes – Formation of new
Cells by Cell Division
• Cell division occurs in
humans & other
organisms at different
times in their lives
• The type of cell division
differs depending on the
organism & why the cell
is dividing
• Reproduction, growth,
development, repair, or
asexual reproduction, or
formation of gametes
• Gametes – an
organism’s
reproductive cellssuch as sperm or
ovum (egg) cells
• All information stored
in DNA must be
present in each
resulting cells
• DNA is first copied –
then distributed
• Each cell ends up
with a complete set
(copy) of DNA
Prokaryotic Cell Reproduction
• Prokaryote’s single DNA
molecule is circular & is
attached to the inner cell
membrane
• Binary fission – a form
of asexual reproduction
that produces identical
offspring
• Occurs in 2 stages –
1st,DNA is copied 2nd,
cell divides
Binary fission animation
• http://highered.mcgrawhill.com/sites/9834092339/student_view0/
chapter10/animation_-_cell_division.html
• http://www.classzone.com/books/hs/ca/sc/
bio_07/animated_biology/bio_ch05_0149_
ab_fission.html
Bacterial Growth
• http://www.ryancshaw.com/Files/micro/Ani
mations/BacterialGrowth/micro_bacterial_
growth.swf
Eukaryotic Cell Reproduction
• Information
encoded in DNA
organized into
units called
genes
• Gene- a segment
of DNA that codes
for a protein or
RNA molecule
• Genes play an
important role in
determining how
a person’s body
develops &
functions
• Chromosomes – the DNA &
the proteins associated with
DNA- are copied and
become visible
• Chromatids – the exact
copies of DNA that make up
each chromosome
• Centromere – point of
attachment of the chromatids
• Chromatids become
separated during cell
division, new cell will have
same genetic information as
original cell
How Chromosome Number and
Structure Affect Development
• Somatic cell – any cell
other than sperm or egg
cell
• Humans normally has
two copies of 23
different chromosomes
which differ in size,
shape, and set of genes
• Each chromosome
contains thousands of
genes which
determines how you
develop & function
Sets of Chromosomes
• Homologous
chromosomeschromosomes that are
similar in size, shape,
and genetic content
• 23 – from each parent
• Diploid- containing two
sets of chromosomes,
such as somatic cells
• Haploid- contains one
set of chromosomes,
such as gametes
• The symbol n is
used to represent
one set of
chromosomes
• Zygote- is a
fertilized egg cell,
the first cell of a
new individual
• Each organism
has a
characteristic
number of
chromosomes
• P. 121 Table 1
see chart
Sex Chromosomes
• Autosomeschromosomes that are
not directly involved in
determining the sex
(gender) of an individual
in humans 22 pairs
• Sex chromosomes –
contain genes that will
determine the sex of the
individual
• Often referred to as “X”
and “Y” chromosomes
• In humans, a female is
XX; while a male is XY
• The structure & number
of sex chromosomes
vary in different
organisms
• Some insects there is no
Y chromosome- the
female is XX, but the
male is XO (O indicates
the absence of a
chromosome)
• In birds, moths, &
butterflies, the male has
two X, while female has
only one
Change in Chromosome Number
• The presence of all 46
chromosomes is
essential for normal
development & function
• Trisomy- humans with
more than two copies of
a chromosome, will not
develop properly
• Karyotype-a photo of
the chromosomes in a
dividing cell that shows
the chromosomes
arranged by size
Make a Karotype
• http://learn.genetics.utah.edu/content/begi
n/traits/karyotype/
• Trisomy 21(an extra 21
chromosome), also
Down syndrome all have
similar characteristics
• Mothers younger than
30,1 in 1500 births
• Mothers 37 & older, 1 in
290 births
• Mothers over 45, as high
as 1 in 45 births
• As a female ages, her
eggs can accumulate an
increasing amount of
damage
• Disjunction-when sperm
and egg cells form, each
chromosome & its
homologue separate
• Nondisjunctionchromosomes fail to
separate-one new
gamete ends up with
both chromosomes & the
other gamete none
• Trisomy occurs when the
gamete with both
chromosomes fuses with
a normal gamete
Prenatal Testing
• Amniocentesis
• Choriconic villi
Change in Chromosome Structure
• Mutations- change in
an organism’s
chromosome structure
• Deletion- a piece of a
chromosome breaks off
completely- can be fatal
• Duplication-a
chromosome fragment
attaches to its
homologous
chromosome, which will
now carry two copies of
certain set of genes
• Inversion – the
chromosome piece
reattaches to the original
chromosome but in
reverse orientation
• Translocation-a piece
reattaches to a
nonhomologous
chromosome
Homework
• Do section 1 key terms (definitions) 13
words
• Section 1 review p. 124
• Questions 1-5 write the question
The Cell Cycle
section 2
Cell Cycle
• http://www.wisconline.com/objects/ViewObject.aspx?ID=A
P13604
The Life of a Eukaryotic Cell
• The Cell Cycle is a
repeating sequence of
cellular growth and
division during the life of
an organism
• Cell usually spends 90%
of its time in the first 3
phase of the cycle,
which are called
interphase
• Last 2 phases of cell
cycle will only occur if
the cell is about to divide
• First growth (G1) phasecell grows rapidlycarries out routine
functions- some cells
stay in this phase
• Synthesis (S) phaseCell’s DNA is copied-two
chromatids attached at
the centromere
• Second growth (G2)
phase- preparations are
made for the nucleus to
divide – microtubules are
rearranged in
preparation for mitosisrepair of DNA mistakes
Cell Cycle Animation
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/
chapter2/animation__how_the_cell_cycle_
works.html
• Mitosis- process
during cell division in
which the nucleus of a
cell is divided into two
nuclei-same number &
kinds of chromosomes
as original cell
• Cytokinesis- the
process during cell
division in which the
cytoplasm divides
• Cell cycle may be
summarized as
follows:
G1 - S – G2 - M - C
Cell cycle virtual lab
• http://bio.rutgers.edu/~gb101/lab2_mitosis/
index2.html
Control of the Cell Cycle
• Cells have a set of
“red light-green light”
switches that are
regulated by
feedback information
from the cell
• Cell cycle is
controlled by many
proteins
• Cell growth (G1)
checkpoint- makes
the decision of
whether the cell will
divide
• During S phase, DNA is copied, if conditions not
favorable, cells can typically stop the cell cycle
• DNA synthesis (G2) checkpoint - DNA repair enzymes
check DNA replication – if okay, mitosis occurs
• Mitosis checkpoint – triggers the exit of mitosis – also
signals the beginning of the G1 phase
When Control is Lost: Cancer
• Genes contain
information necessary to
make proteins
• Proteins control cell
growth & development
• Cancer- uncontrolled
growth of cells – a
disorder of cell division
• Mutations over
producing growthpromoting molecules or
inactivating the control
proteins that act to slow
or stop cell cycle
Cancer Map
• http://www.insideca
ncer.org/
Cancer Biology
• http://www.cancerquest.org/images/Docu
mentary/English/DocInterfaceEng.swf
Homework
• Section 2 review 1-4 page 127
• Section 2 Key terms page125
• Chapter review page 134
2, 7-8,12,14,17
Mitosis & Cytokinesis
section 3
• Cells receiving the signal
to divide continue past
the G2 phase – enter the
last 2 phases of the cell
cycle-mitosis &
cytokinesis
• During mitosis,
chromatids are
physically moved to
opposite sides of the
dividing cell with the help
of spindles
Forming the Spindle
• Spindle-cell structure made
of both centrioles &
microtubule fibers that move
chromosomes during cell
division
• Centrosome – organelle that
organizes the assembly of
the spindle
• Centrioles & spindle fibers of
hollow tubes of protein –
microtubules
• Spindle fiber-individual;
centrioles- 9 triplets arranged
in a circle
• Plants don’t have centrioles
Separation of Chromatids by
Attaching Spindle Fibers
• Microtubules attach to
the centromeres & poles,
the two chromatids can
be separated
• Once separated, the
chromatids move along
paths described by
microtubules
• When chromatids are
separated, they are
called chromosomes
Mitosis & Cytokinesis
• Divided into 4 phases:
• Step 1 Prophase –
chromosomes coil up
& become visible;
nuclear envelope
dissolves & a spindle
fiber forms
• Step 2 Metaphase –
chromosomes move to
the center of the cell &
line up along the
equator; spindle fibers
link the chromatids of
each chromosome to
opposite poles
• Step 3 Anaphase –
chromatids divide (now
called chromosomes)
move toward opposite
poles as spindle fibers
shorten
• Step 4 Telophase –
nuclear envelope forms
around the
chromosomes at each
pole; chromosomes
begin to uncoil & spindle
dissovles & disappear –
• Mitosis complete
Cytokinesis
• The cytoplasm divides in
half, cell membrane
grows to enclose each
cell, forming two
separate cells
• Two genetically cells
where there was one
• Cells lacking cell walls,
the cell is pinched in half
by protein threads
• Cells with cell wall - vesicles formed by Golgi
apparatus fuse at midline to form cell plate
• Cell wall forms on either side of cell plate
• Offspring cells – about equal size; identical copy
of the original chromosomes; & receives about
½ of original cytoplasm & organelles
Homework
• Write question
• Section 3 Review page 132 1-4
• Chapter review page 134
1,3-6,9,10,11
STP 1-3
Bonus
Page 129 Calculating the number of cells
resulting from Mitosis 1-3 show work