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Chapter 8 pelican Ch 12 AP
The Cellular Basis of
Reproduction and Inheritance
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Rain Forest Rescue
• Scientists in Hawaii are attempting to "rescue"
endangered species from extinction by
promoting reproduction
• Reproduction is one phase of an organism's
life cycle
– Sexual reproduction
• Fertilization of sperm and egg produces
offspring
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Rain Forest Rescue
– Asexual reproduction
• Offspring are produced by a single parent,
without the participation of sperm and egg
• Cell division is at the heart of organismal
reproduction
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Connections b/w Cell Division & Reproduction
8.1 Like begets like, more or less
8.2 Cells arise only from preexisting cells
8.3 Prokaryotes reproduce by binary fission
Like Begets like, more or less
• Asexual reproduction – creation of offspring by
one parent, without sperm or egg.
– Ex: Amoebas
– Chromosomes are duplicated and cell divides
– Each daughter cell is genetically identical to
the parent and the other daughter
• Sexual reproduction
– Each offspring inherits a unique combination
of genes from both parents
– Offspring can show great variation
Video: Hydra Budding
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Amoeba producing genetically identical offspring through asexual
reproduction
Sexual Reproduction produces offspring with unique combinations of genes
8.2 Cells arise only from preexisting cells
•
Rudolf Virchow stated, “Where a cell exists, there
must have been a preexisting cell.”
•
"Every cell from a cell" is at the heart of the
perpetuation of life – cell division
– Cell Division can reproduce an entire
unicellular organism
– Is the basis of sperm and egg formation
– Allows for development from a single cell
(zygote or fertilized egg) into an adult organism
– Functions in an organism's renewal and repair,
replacing cells that die
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.3 Prokaryotes reproduce by binary fission
• Prokaryotic cells reproduce asexually by a type
of cell division called binary fission (dividing in
half)
– Genes are on one circular DNA molecule
– The cell replicates its single chromosome
– The chromosome copies move to opposite
ends of the cell
– The cell elongates
– The plasma membrane grows inward,
dividing the parent into two daughter cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-3a
Plasma
membrane
Prokaryotic
chromosome
Cell wall
Binary Fission of a
Prokaryotic cell
Duplication of chromosome
and separation of copies
Continued elongation of the
cell and movement of copies
Division into
two daughter cells
LE 8-3b
Dividing Bacterium
Colorized TEM 32,500
Prokaryotic chromosomes
The Eukaryotic Cell Cycle and Mitosis
• 8. 4 The large, complex chromosomes of eukaryotes
duplicate with each cell division.
• 8.5 The cell cycle multiplies cells.
• 8.6 Cell division is a continuum of dynamic changes.
• 8.7 Cytokinesis differs for plant & animal cells.
• 8.8 Anchorage, cell diversity, & chemical growth factors
affect cell division.
• 8.9 Growth factors signal the cell cycle control system.
• 8.10 Growing out of control, cancer cells produce
malignant tumors.
• 8.11 Review of the functions of mitosis: Growth, cell
replacement, and asexual reproduction.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division
• Eukaryotic genes
– Many more and larger than in prokaryotes
• Human cells have 30,000 genes and
bacteria cells have 3,000 genes
– Genes are grouped into multiple
chromosomes in the nucleus
Plant cell (from African
Blood lily) just before
division
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division
• Eukaryotic chromosomes
– Contain a very long DNA molecule
associated with proteins
– Most of the time occur in the form of thin,
loosely packed chromatin fibers, which is a
combination of DNA and protein molecules.
– Condense into visible chromosomes just
before cell division
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division
• Eukaryotic cell division
– Chromosomes replicate
• Sister chromatids joined together at the
centromere
– Sister chromatids separate
• Now called chromosomes
– Cell divides into two daughter cells
• Each with a complete and identical set of
chromosomes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-4b
Sister chromatids
In humans, a cell has 46
duplicating chromosomes
(92 chromatids) and each
of the 2 daughter cells
results in 46 single
chromosomes
Centromere
LE 8-4c
Chromosome
duplication
Centromere
Sister
chromatids
Chromosome
distribution
to
daughter
cells
8.5 The cell cycle multiplies cells
• The cell cycle is an ordered series of events
extending from the time a cell is formed until it
divides into two cells
• Cell Cycle consists of interphase & mitotic phase
• Most of the cell cycle is in interphase (90% of
time required for cell cycle
– G1: cell grows in size
– S: DNA synthesis (replication) occurs
– G2: Cell continues to grow and prepare for
division
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.5 The cell cycle multiplies cells
• The cell actually divides in mitotic (M) phase
– Accounts for 10% of time needed for cell
cycle
– Mitosis: nuclear division
• Nucleus and duplicated chromosomes
divide and are evenly distributed forming 2
daughter nuclei
– Cytokinesis: cytoplasmic division (cytoplasm
divides into 2)
– Duplicated chromosomes evenly distributed
into two daughter nuclei
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-5
INTERPHASE
S
(DNA synthesis)
G1
G2
8.6 Cell division is a continuum of dynamic changes
• Interphase: Duplication of the genetic material
ends when chromosomes begin to become
visible
• Prophase (the first stage of mitosis): The
mitotic spindle is forming. Centrosomes
migrate to opposite ends of the cell
• Prometaphase: Chromatins completely coil
into chromosomes; nucleoli and nuclear
membrane disperse
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.6 Cell division is a continuum of dynamic changes
• Metaphase: The spindle is fully formed;
chromosomes are aligned single file with
centromeres on the metaphase plate
• Anaphase: Chromosomes separate from the
centromere, dividing to arrive at poles
• Telophase: Cell elongation continues, a
nuclear envelope forms around chromosomes,
chromosomes uncoil, and nucleoli reappear
• Cytokinesis: The cytoplasm divides
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-6a
INTERPHASE
Centrosomes
(with centriole pairs)
Nucleolus
Nuclear
envelope
PROPHASE
Chromatin
Plasma
membrane
Early mitotic
spindle
PROMETAPHASE
Centrosome
Chromosome, consisting
of two sister chromatids
Centromere
Fragments
of nuclear
envelope
Kinetochore
Spindle
microtubules
LE 8-6b
METAPHASE
ANAPHASE
Cleavage
furrow
Metaphase
plate
Spindle
TELOPHASE AND CYTOKINESIS
Daughter
chromosomes
Nuclear
envelope
forming
Nucleolus
forming
Video: Animal Mitosis
Video: Sea Urchin (time lapse)
Animation: Mitosis (All Phases)
Animation: Mitosis Overview
Animation: Late Interphase
Animation: Prophase
Animation: Prometaphase
Animation: Metaphase
Animation: Anaphase
Animation: Telophase
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.7 Cytokinesis differs for plant and animal cells
• Animals
– Ring of microfilaments contracts into
cleavage furrow, shallow groove in the cell
surface.
– When actin microfilaments interact with
myosin, ring contracts, like pulling
drawstrings
– Cleavage occurs deepening and pinches
the parent cell in 2, producing 2 separate
cells, each with own nucleus and
cytoplasm.
Animation: Cytokinesis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-7a
Cleavage of
Animal Cell
Cleavage
furrow
Cleavage furrow
Contracting ring of
microfilaments
Daughter cells
8.7 Cytokinesis differs for plant and animal cells
• Plants
– Vesicles fuse into a membranous cell plate
– Cell plate fuses with plasma membrane
– Cell plate develops into a new wall between
two daughter cells bounded by its own
plasma membrane and cell wall
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-7b
Cell plate
forming
Wall of
parent cell
Daughter
nucleus
Cell plate
formation in a
Plant Cell
Cell wall
Vesicles containing
cell wall material
New cell wall
Cell plate
Daughter cells
8.8 Anchorage, cell density, and chemical growth factors affect cell division
• An organism must be able to control the timing
of cell division
• Humans, skin cells and cells lining digestive tract
divide replacing cells that are being abraded and
sloughed off.
• In contrast, human liver does not divide unless
liver is damaged. Cell division = repairs wounds
• Anchorage dependence
– Most animal cells must be in contact with a
solid surface (matrix of tissue or culture dish)
to divide
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.8 Anchorage, cell density, and chemical growth factors affect cell division
• Density-dependent inhibition
– Cells form a single layer & cells stop
dividing when they touch one another
– If cells are removed, then cells will begin
dividing again until space is filled
– Ex: cut yourself, skin cells around the cut
begin dividing and healing occurs to fill gap
– Inadequate supply of growth factor, protein
secreted by certain body cells that
stimulates other cells to divide, causes
division to stop
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-8a
Cells anchor to
dish surface
and divide.
When cells have
formed a complete
single layer, they
stop dividing
(density-dependent
Inhibition).
If some cells are
scraped away, the
remaining cells
divide to fill the dish
with a single layer
and then stop
(density-dependent
inhibition).
LE 8-8b
After forming a
single layer,
cells have
stopped dividing.
Providing an
additional supply of
growth factors
stimulates
further cell division.
8.9 Growth factors signal the cell cycle control system
• The cell cycle control system regulates the
events of the cell cycle
– Not like a set of dominoes but proteins must
trigger the separation of sister chromatids
marking the start of the next phase.
• If a growth factor is not released at three major
checkpoints, the cell cycle will stop
– G1 of interphase
– G2 of interphase
– M phase
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-9a
G1 checkpoint
G0
Control
system
G1
M
M checkpoint
G2 checkpoint
G2
S
8.9 Growth factors signal the cell cycle control system
•
How a growth factor might affect the cell cycle
control system
– Cell has receptor protein in plasma membrane
– Binding of growth factor to receptor triggers a
signal transduction pathway leading to cell
division
– “Signals” are changes that molecules
induces in the next molecule pathway.
– Signal reaches cell cycle control system &
overrides brakes on the cell cycle control
system preventing progress
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-9b
Growth factor
Plasma membrane
Relay
proteins
Receptor
protein
Signal
transduction
pathway
G1 checkpoint
Control
system
G1
M
How a growth factor signals
the cell cycle control system
S
G2
8.10 Growing out of control, cancer cells produce malignant tumors
• Cancer claims the lives of 1 out of every 5
people in US and other developing nations
• Cancer cells do not respond normally to the
cell cycle control system
– Divide excessively
– Can invade other tissues
– May kill the organism
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.10 Growing out of control, cancer cells produce malignant tumors
•
Single cell undergoes transformation, process converts
normal cell to cancer cell.
– The body’s immune system usually recognizes the
transformed cell as abnormal and destroys it.
•
If an abnormal cell avoids destruction by the immune
system, it may form a tumor, abnormal mass growing
body mass of body cells.
– Benign: abnormal cells remain at original site & can
be removed by surgery
– Malignant: abnormal cells can spread to other tissues
and parts of the body (has cancer)
– Metastasis: spread of cancer cells through the
circulatory system
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-10
Growth and metastasis of a malignant (cancerous) tumor
Lymph
vessels
Tumor
Blood
vessel
Glandular
tissue
A tumor grows from a
single cancer cell.
Cancer cells invade
Neighboring tissue.
Cancer cells spread through
lymph and blood vessels to
other parts of the body.
8.10 Growing out of control, cancer cells produce malignant tumors
•
Cancers are named according to location of origin
– Carcinoma: external or internal body coverings
(skin or lining of intestines)
– Sarcoma: tissues that support the body (bones
and muscles)
– Leukemia and lymphoma: blood-forming
tissues (bone marrow, spleen, & lymph nodes)
– Cancer Cells don’t exhibit density-dependent
inhibition, they continue to divide even if they
have to pile up on one another
– Many have defective cell cycle control systems
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.10 Growing out of control, cancer cells produce malignant tumors
• Tumors localized may be removed by surgery
• Radiation and chemotherapy are effective as
cancer treatments because they interfere with cell
division
• Radiation damages DNA in cancer cells b/c
cancer cells have lost the ability to repair
damage
• Damage to normal cells causing bad side
effects such as sterility.
• Chemo side effects are due to the drug’s
effects on normal cells that rapidly divide like
nausea from intestinal cells, hair loss from
follicle cells, & infection from immune cells.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.10 Growing out of control, cancer cells produce malignant tumors
• Chemotherapy Drugs
• Paclitaxel ( Taxol) - “freezes” the mitotic
spindle, which stops actively dividing cells fro
proceeding past metaphase.
• Found in bark of Pacific yew tree in
northwestern US
• Vinblastin – prevents spindles from forming in
the first place
• Found in periwinkle plant found in
Madagascar rain forest
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.11 Review of the functions of mitosis: growth, cell replacement, and asexual reproduction
• When the cell cycle operates normally, mitotic
cell division functions in
– Growth
– Replacement of damaged or lost cells
– Asexual reproduction
Video: Hydra Budding
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Growth in an onion root
Cell replacement in bone marrow
Asexual reproduction
Meiosis and Crossing Over
• 8.12 Chromosomes are matched in homologous pairs.
• 8.13 Gametes have a single set of chromosomes
• 8.14 Meiosis reduces the chromosome number from
diploid to haploid
• 8.15 Review: A comparison of mitosis & meiosis
• 8.16 Independent orientation of chromosomes in meiosis
and random fertilization lead to varied offspring.
• 8.17 Homologous chromosomes carry different versions
of genes.
• 8.18 Crossing over further increases genetic variability.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.12 Chromosomes are matched in homologous pairs
• The somatic (body) cells of each species contain
a specific number of chromosomes, humans
have 46 chromosomes.
• Humans and most other organisms have pairs of
homologous chromosomes, 2 chromosomes
composing a pair.
– Carry genes for the same characteristics at
the same place, or locus
• Except sex chromosomes XX and XY
– One chromosome is inherited from the female
parent, one from the male
– Autosomes, other 22 pairs of chromosomes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-12
Chromosomes
Homologous Pair of
Chromosomes
Centromere
Sister chromatids
8.13 Gametes have a single set of chromosomes
• Diploid cells have two sets of chromosomes
(2n)
– Humans = diploid # = 46
– Somatic cells
• Haploid cells have one set of chromosomes (n)
– Gametes (egg and sperm cells)
• Sexual life cycles involve the alternation of
haploid and diploid stages
– Fusion of haploid gametes in fertilization
forms a diploid zygote (1haploid set from
mom and one set from dad)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-13
Haploid gametes (n = 23)
n
Egg cell
n
Sperm cell
Meiosis
Fertilization
Diploid
zygote
(2n = 46)
Multicellular
diploid adults
(2n = 46)
Mitosis and
development
2n
8.14 Meiosis reduces the chromosome number from diploid to haploid
• Meiosis – type of cell division that produces
gametes in diploid organisms
– Like mitosis, is preceded by chromosome
duplication
– Unlike mitosis, cell divides twice to form four
haploid daughter cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.14 Meiosis reduces the chromosome number from diploid to haploid
• The process of meiosis includes two
consecutive divisions
– Meiosis I
• In synapsis, homologous chromosomes are
paired
• In crossing over, homologous chromosomes
exchange corresponding segments
• Each homologous pair divides into two
daughter cells, each with one set of
chromosomes consisting of two chromatids
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.14 Meiosis reduces the chromosome number from diploid to haploid
• Meiosis II
– Essentially the same as mitosis
– Sister chromatids of each chromosome
separate
– Result is four cells, each with half as many
chromosomes as the parent
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.14 Meiosis reduces the chromosome number from diploid to haploid
Animation: Meiosis Overview
Animation: Interphase
Animation: Prophase I
Animation: Metaphase I
Animation: Anaphase I
Animation: Telophase I and Cytokinesis
Animation: Telophase II and Cytokinesis
Animation: Prophase II
Animation: Metaphase II
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-14a
MEIOSIS I : Homologous chromosome separate
INTERPHASE
PROPHASE I
METAPHASE I
ANAPHASE I
Centrosomes
(with centriole
pairs)
Microtubules
Sister chromatids
Sites of crossing over attached to Metaphase remain attached
plate
kinetochore
Spindle
Nuclear
envelope
Sister
chromatids
Chromatin
Tetrad Centromere
(with kinetochore)
Homologous
chromosomes separate
LE 8-14b
MEIOSIS II : Sister chromatids separate
TELOPHASE I
AND CYTOKINESIS
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II
AND CYTOKINESIS
Cleavage
furrow
Sister chromatids
separate
Haploid daughter
cells forming
8.15 Review: A comparison of mitosis and meiosis
• Mitosis
– Provides for growth, tissue repair, and
asexual reproduction
– Produces daughter cells genetically
identical to the parent
• Meiosis
– Needed for sexual reproduction
– Produces haploid daughter cells with one
member of each homologous chromosome
pair
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-15
MITOSIS
MEIOSIS
Site of
crossing over
Parent cell
(before chromosome replication)
MEIOSIS I
Prophase I
Prophase
Tetrad formed
by synapsis of
homologous
chromosomes
Chromosome
replication
Chromosome
replication
Duplicated
chromosome (two
sister chromatids)
2n = 4
Chromosomes
align at the
metaphase plate
Metaphase
Anaphase
Telophase
Sister chromatids
separate during
anaphase
2n
2n
Daughter cells
of mitosis
Tetrads
align at the
metaphase plate
Metaphase I
Anaphase I
Telophase I
Homologous
chromosomes
separate during
anaphase I;
sister
chromatids
remain together
No further
chromosomal
replication;
sister
chromatids
separate during
anaphase II
Haploid
n=2
Daughter
cells of
meiosis I
MEIOSIS II
n
n
n
Daughter cells of meiosis II
n
8.16 Independent orientation of chromosomes in meiosis and
random fertilization lead to varied offspring
• Reshuffling of the different versions of genes during
sexual reproduction produces genetic variation
– Random arrangements of chromosome pairs at
metaphase I of meiosis lead to many different
combinations of chromosomes
– Random fertilization of eggs by sperm greatly
increases this variation
– 50% chance that a daughter cell will get the
maternal chromosome of a certain homologous pair
and 50% chance that it will receive the paternal
chromosome.
– Total # of combinations of chromosomes = 2n
– Human (n=23) 223 = 8 million possible
combinations
Animation: Genetic Variation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-16
Possibility 1
Possibility 2
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Gametes
Combination 1
Combination 2
Combination 3
Combination 4
8.17 Homologous chromosomes carry different versions of genes
• Each chromosome of a homologous pair can
bear different versions of genes at
corresponding loci
– Makes gametes (and thus offspring)
different from one another
– Examples: coat color and eye color in mice
Brown coat (C); black eyes (E)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
White coat (c); pink eyes (e)
LE 8-17a
Coat-color
genes
Eye-color
genes
Brown
Black
C
E
C
E
C
E
c
e
c
e
Meiosis
c
e
White
Pink
Tetrad in parent cell
(homologous pair of
duplicated chromosomes)
Chromosomes of
the four gametes
8.18 Crossing over further increases genetic variability
• Crossing over is a genetic rearrangement
between two homologous chromosomes
– Homologues pair up into a tetrad, 4
chromatids, during prophase I of meiosis
which are attached at the centromere
– Maternal and paternal chromatids break at
the same place
– The two broken chromatids join together in
a new way at the chiasma, which is where
crossing over appears as a X-shaped
region
Animation: Crossing Over
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
TEM 2,200
LE 8-18a
Tetrad
Chiasma
Centromere
8.18 Crossing over further increases genetic variability
– When homologous chromosomes separate at
anaphase I, each contains a new segment
– In meiosis II, each sister chromatid goes to a
different gamete
– Gametes of four genetic types result due to
crossing over resulting in genetic
recombination, production of gene
combinations different from those carried by
the original chromosomes.
– Different versions of genes that homologous
chromosomes may have arise from mutations,
so mutations are responsible for genetic
diversity
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-18b
Coat-color
genes
Eye-color
genes
C
E
Tetrad
(homologous pair of
chromosomes in synapsis)
c
e
Breakage of homologous chromatids
C
E
c
e
Joining of homologous chromatids
C
E
Chiasma
c
e
Separation of homologous
chromosomes at anaphase I
C
E
C
e
c
E
c
e
Separation of chromatids at
anaphase II and
completion of meiosis
C
E
Parental type of chromosome
C
e
Recombinant chromosome
c
E
c
e
Recombinant chromosome
Parental type of chromosome
Gametes of four genetic types
Alterations of chromosome number and structure
• 8.19 A karyotype is a photographic inventory of
an individual’s chromosomes.
• 8.20 An extra copy of chromosome 21 causes
Down Syndrome.
• 8.21 Accidents during meiosis can alter
chromosome number
• 8.22 Abnormal numbers of sex chromosomes
do not usually affect survival
• 8.23 Alterations of chromosome structure can
cause birth defects and cancer
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.19 A karyotype is a photographic inventory of
an individual's chromosomes
•
A blood sample is treated with a chemical that
stimulates mitosis
•
After several days, another chemical arrests mitosis at
metaphase, when chromosomes are most highly
condensed
•
Chromosomes are photographed and electronically
arranged by size and shape into the karyotype,
ordered display of magnified images of an individual’s
chromosomes arranged in pairs, starting with longest.
•
Normal humans have 22 pairs of autosomes and two
sex chromosomes
•
Trisomy 21 is detected through karyotyping
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-19
Packed red and
white blood cells
Blood
culture
Hypotonic
solution
Fixative
White
blood
cells
Centrifuge
Stain
Fluid
Centromere
Siste
c
r hromatids
2,600
Pair of homologous
chromosomes
8.20 An extra copy of chromosome 21 causes Down syndrome
• A person has 23 pairs of chromosomes but may
have abnormal number of chromosomes
– In most cases, human embryo with abnormal
number of chromosomes is aborted
• Down syndrome is caused by trisomy 21, an
extra copy of chromosome 21
– The most common human chromosome
number abnormality, 1 out of 700 kids born
– Many physical and mental problems
– Increased incidence in older mothers, testing
done to women over the age of 35
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
A karyotype of trisomy 21
Child with Down Syndrome
Round face, skin fold at inner
corner of eyes, flattened nose
bridge, small, irregular teeth,
short statue, heart defects,
Susceptibility to leukemia,
Alzheimer’s Disease, and
respiratory infections, Varying
degrees of mental retardation
LE 8-20c
8.21 Accidents during meiosis can alter chromosome number
• Abnormal chromosome count is a result of
nondisjunction
– The failure of homologous pairs to separate
during meiosis I
• The failure of sister chromatids to separate
during meiosis II with 2 gametes normal and 2
gametes abnormal
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-21a
LE 8-21b
LE 8-21c
Fertilization of an egg resulting from nondisjuction with a
normal sperm results in a zygote with an abnormal
chromosome number
May be involved in Trisomy 21
8.22 Abnormal numbers of sex chromosomes do not usually affect survival
• Nondisjunction can produce gametes with
extra or missing sex chromosomes
– Upset the genetic balance less than
unusual numbers of autosomes
– Lead to varying degrees of malfunction in
humans
– Usually do not affect survival
– P. 147 (next to last paragraph)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
8.22 Abnormal numbers of sex chromosomes do not usually affect survival
8.23 Alterations of chromosome structure can cause birth defects and cancer
•
Breakage can lead to rearrangements affecting genes
on one chromosome
– Deletion: loss of a fragment of chromosome
– Duplication: addition of a fragment to sister
chromatid
– Inversion: reattachment of a fragment in reverse
order
– Inversions least harmful because all genes are
present in normal number
– Deletions cause serious physical & mental
problems
• Ex: cri du chat (child is mentally retarded with small
head and unusual face features, & has a cry of
distressed cat – usually die in infancy)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-23a
8.23 Alterations of chromosome structure can cause birth defects and cancer
• Translocation is the attachment of a
chromosomal fragment to a nonhomologous
chromosome
– Can be reciprocal
– May or may not be harmful
– Some people with Down Syndrome have
only part of a 3rd chromosome 21 as a result
of translocation it is attached to another
chromosome
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-23b
8.23 Alterations of chromosome structure can cause birth defects and cancer
• Chromosomal changes in sperm or egg cells can
cause congenital disorders
• Chromosomal changes in a somatic cell may
contribute to the development of cancer
• Ex: Chromosomal translocation in somatic cells
in the bone marrow is associated with chronic
myelogenous leukemia
– Affects cells that give rise to white blood cells
– Part of chromosome 22 has switched places
with a small fragment from a tip of
chromosome 9
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-23c