Cellular Basis of Reproduction and Inheritance

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Chapter 8

• Cellular Basis of Reproduction and Inheritance

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• 8.1 Like begets like, more or less
• Some organisms reproduce asexually
• And their offspring are genetic copies of the
  parent and of each other

Figure 8.1A
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• Other organisms reproduce sexually
• Creating variety in the offspring

Figure 8.1B
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8.3 Prokaryotes reproduce by binary fission

• As the cell replicates its single chromosome,
  the copies move apart
• And the growing membrane then divides the cells

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One-celled protists also do fission, but must do
mitosis first to divide chromosomes evenly
Prokaryotic chromosomes
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8.4 Chromosomes of eukaryotes duplicate in cell
division
Eukaryotic cells have many chromosomes
each contains thousands of genes - are visible
only when the cell is dividing Before cell
division - DNA replicates a. helicase unzips
molecule b. templates original strands c.
Polymerase base-pairing rules ? two identical
molecules
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DNA condenses
Before a cell divides, it packs its DNA into
CHROMOSOMES - ALREADY COPIED (replicated)
- tightly packed and condensed -
keeps copies organized and intact until
cell splits
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DNA
chromatin
DNA wraps around histones
Groups of histones form nucleosomes
These group to form chromatin
This coils and wraps until it all fits into the
nucleus.
One chromosome (copied and packed for cell
division)
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SEM of human chromosomes
Sister chromatids identical copies
Centromere holds chromatids together
Prokaryotes have a single, circular chromosome
- no histones no nucleus
Double-stranded (replicated) chromosome
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• 8.5 The cell cycle multiplies cells
• The cell cycle consists of two major phases

Figure 8.5
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Cell Cycle
INTERPHASE - non-dividing cells - normal
function - most of cell life MITOTIC PHASE -
cell divides ? 2 new cells   G1 ? growth,
normal life functions S ? synthesis DNA
replicates G2 ? final growth prepares to divide
INTERPHASE
MITOTIC PHASE
Mitosis chromosomes condense, organize and
divide - each new cell gets one copy of every
chromosome Cytokinesis cytoplasm divides
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• The stages of cell division

Figure 8.6 (Part 1)
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PHASES OF MITOSIS

• PROPHASE cell organizes and prepares
• chromatin
• nuclear membrane, nucleolus
• spindle and asters
• centrioles

• PROMETAPHASE chromosomes condensed
• move toward middle
• centrioles to opposite poles
• spindle

• METAPHASE chromosomes in middle
• Centromeres and spindle fibers

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Figure 8.6 (Part 2)
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• ANAPHASE -chromosomes separate
• spindle fibers pull
• single copies to opposite poles of cell

• TELOPHASE return to normal
• chromosomes relax/uncoil into chromatin
• nuclear membranes form nucleoli appear
• spindle fibers disappear

• CYTOKINESIS - division of cytoplasm
• identical daughter cells

Cleavage furrow
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Cell division differs for plant and animal cells

• 8.7 Animal cytokinesis
• Microfilaments
• Cleavage furrow
• Pinch cytoplasm in two

Figure 8.7A
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In plants - no centrioles, asters (but
spindle) - cell plate - new cell wall grows
along sides of cell plate
Figure 8.7B
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(No Transcript)
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Control of Cell Division

• Chemical signals tell a cell when to divide
• Normal rate growth, repair
• - asexual reproduction in some organisms
• Slow rate some cell types divide rarely
  (liver)
• - aging ? slow healing, lose some cells
• Fast rate some cell types (skin, digestive
  lining)
• Uncontrolled ? cancer

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Cell cycle checkpoints

• Check cell conditions - Cycle wont proceed
  unless okay
• G1 checkpoint Cell has enough materials?
• - Yes? Go to S No? Go to G0 (nondividing)
• G2 checkpoint DNA copied correctly? Yes? Go to
  M
• M checkpoint ( in metaphase)
• - chromosomes lined up correctly?
• - centromeres attached to spindle?

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• Growth factors cyclins
• Chemicals secreted by cells
• Can start or stop cell division

Figure 8.8B
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Anchorage and Contact Inhibition

• Anchored to a solid substance
• - ex. Extracellular matrix
• Contact stop dividing when they touch other
  cells
• - density-dependent

Figure 8.8A
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Programmed Cell Deathapoptosis

• Cells damaged too much to repair
• self-destruct
• 2. Embryonic development lose unneeded cells

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8.10 Cancer uncontrolled cell division

• Cancer cells ignore cycle controls
• Repeated and rapid cell divisions
• tumor mass of non-functioning cells
• Benign not cancer do not spread to nearby
  tissue
• May get so large it stops tissue function
• Malignant tumor cancer
• Will invade and destroy neighboring tissue
• Metastatic tumor spreads to other body parts
• Starts new cancers

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Cells begin to divide abnormally Continue
dividing, invade healthy tissue Spread through
blood or lymph stream, can start new tumors
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• If not treated early, cancer will spread
• - kills by destroying organ function

Figure 8.10
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The most common cancer - skin
Most dangerous - MELANOMA
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• Cancer treatment
• Radiation high-energy, carefully aimed at tumor
• Chemotherapy drugs specific for tumor types
• interfere with cell division
• some normal cells destroyed, too
• Skin (lose hair) digestive lining (nausea)
• Surgery remove tumor and nearby cells
• Boost immune system healthy diet, reduce stress

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8.11 Review mitosis Growth, cell replacement,
and asexual reproduction

• Mitosis functions in growth adds new cells

In repair replace old or damaged cells
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In Asexual Reproduction

• One-celled organisms, some simple
  multicelled
• Hydra with bud vegetative
  propagation in plants

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Regeneration replace lost body part

• starfish can replace an arm
  flatworms can regrow a body

Lizards can replace a tail
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Stem cells and differentiation
Differentiate cells specialize as embryo
develops Stem cell unspecialized cell -
can differentiate to form many kinds of cells
- depends on chemical signals from nearby cells
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Stem cells for cloning tissues
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Meiosis Sexual Reproduction
Sexual Reproduction - two parents a. Offspring
are genetic mix of both parents b. Have a NEW
combination of genes Advantage genetic
variation in offspring a. Some may have traits
that favor survival b. Can pass these traits on
to offspring c. Darwins theory - survival of
the fittest d. Variation in individuals allows
species to evolve 
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Crossing over a. Only in meiosis b.
Chromatids trade pieces c. Further increases
genetic variation
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Simple organisms exchange some DNA a.
Bacteria and protists - conjugation
Sexual Reproduction
Complex organisms special cells a. gametes
sperm and egg b. Gametes combine in
fertilization ? zygote ? new
organism
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Chromosome Number Diploid and Haploid

• Somatic (body) cells
• a. have matched chromosome pairs
• - homologous
• - one member of pair from each parent
• - carry genes for the same traits
• b. 22 pairs autosomes one pair sex
  chromosomes X, Y

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Cells with paired chromosomes are diploid a. 2n
(n number) b. Human 2n 46 (23 pairs)
Fruit fly 2n 8
2 sets of chromosomes - 2 sets of genes
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Homologous pairs separate in MEIOSIS
Diploid cell Has pairs (2n2)
TWO cell divisions - Daughter cells have ½
parent chromosome number
Meiosis I Pairs separate (n 1)
Meiosis II copies separate (n 1)
Haploid cells - NO pairs (n 1)
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Sex cells are haploid

• gametes sperm and egg
• Haploid (n) - one set of chromosomes
• - one member from each homologous pair
• human n 23

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Meiosis Reduces the Chromosome Number

• 2n parent cell
• DNA replicates in interphase
• First division pairs separate
• Second division sister chromatids separate
• ? 4 haploid daughter cells

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Sexual Life Cycle

• Alternates between diploid and haploid generations

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Meiosis I homologous pairs separate -
makes two daughter cells, but sister chromatids
are still attached
2n parent cell synapsis
pairs line up pairs separate
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Meiosis II sister chromatids separate ? 4
haploid cells
2n ? n two daughter cells
chromatids 4 daughters
one chromosome set each
separate one set
two copies (sisters)
single copies
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8.15 Review Comparing mitosis and meiosis
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Making sperm and egg
Sperm 2n parent cell ? 4 haploid
sperm Ovum 2n parent cell ? 1 haploid egg
haploid polar bodies
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Ovum needs all the cytoplasm
Sperm needs only DNA - and flagellum - and
mitochondria for power - and acrosome to
penetrate ovum
Ovum and polar body (0.1mm)
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Causes of genetic variation

• 1. Homologous pairs have different genes
• same traits, but may be different forms
• 2. Crossing over homologs trade pieces before
  separating
• 3. Pairs position in Metaphase I
• n pairs ? 2n possible combinations
• 4. Random fertilization of eggs by sperm
• Any egg or sperm is equally likely to be used
• 5. Gene or chromosome mutation
• - Error in replication or cell division

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8.16 Chromosomes line up randomly in meiosis

• Many different gene combinations in haploid
  gametes

Figure 8.16
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When meiosis goes wrong
Nondisjunction - do not separate correctly -
pairs or chromatids
In mitosis ? defective nucleus, cell usually
dies In meiosis ? defective gamete ? wrong
number in zygote
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8.21 Accidents during meiosis can alter
chromosome number
Nondisjunction in meiosis I
Nondisjunction in meiosis II All
gametes abnormal Some gametes
normal
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Wrong chromosome number in zygote ? wrong
number in every cell in organism

• Fertilization after nondisjunction ? trisomy in
  zygote

Trisomy 3
Abnormal chromosome number aneuploidy
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8.22 Abnormal number of sex chromosomes usually
do not affect survival in humans

• Nondisjunction of large chromosomes is usually
  lethal
• Down Syndrome - 21 is very small, carries few
  genes
• In sex chromosomes, leads to varying degrees of
  malfunction, but usually not lethal

Turner X_
Klinefelter XXY
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Abnormalities of Sex Chromosomes in Humans
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8.23 Other chromosome changes can cause birth
defects and cancer

• Chromosomes break pieces lost or rearranged
• - in somatic cells ? increases cancer risk
• - in gametes ? genetic disorders

Translocation
Translocation
Activated cancer-causing gene
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8.19 A karyotype is a picture of a persons
chromosomes
Photographed during mitosis - sorted into
homologous pairs - largest-to-smallest -
sex chromosomes last
Abnormalities visible - missing or extra -
pieces broken or moved - pieces added or lost
autosomes
sex chrom.
Trisomy 21
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Making a karyotype

1. Centrifuge blood, use cells 4. Microphotograph
2. Hypotonic cells swell, chromosomes spread out
   5. Sort by pairs and size
3. Centrifuge again, save white cells, mount

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Nuclear transfer cloning animals
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Chromosome disorders______________

• Abnormal zygote - does mitosis ? every cell has
  same defect
• -- Chromosome mutations affect many body systems
• Down Syndrome extra chromosome 21
• -- most common chromosome number abnormality
• -- characteristic features facial, body build
• -- may have internal defects heart, digestive
  tract
• - varying degrees of mental defects
• - age-related - risk increases with maternal age
• Klinefelter, Turner - abnormal sex chromosomes

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Internal control mechanisms Feedback and repair

• Cells make control factors that can start or stop
  cell division
• 1) Growth factor chemical secreted by cells
  tells other cells when to divide
• - use signal transduction pathway
• - cells crowded ? use up growth factors ? stop
  dividing
• Positive feedback when level of a chemical is
  high ? cell divides
• ex. Cyclins made in cell at constant rate,
  accumulate over time
• - when reach a certain level, cell divides
• 3) Negative feedback when level of a chemical
  is low ? cell divides
• - normal number of cells ? normal level of
  chemical
• - some cells missing or damaged ? level drops
  ? cells divide Repair chemicals check for
  damage and fix errors in DNA
• - if damaged beyond repair, cell self-destructs
• - apoptosis programmed cell death
• ex. p53 control chemical, cancer research on
  how it works

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Types of Cancer

• Name tells type of tissue
• Carcinoma epithelial tissue - skin, linings
• Sarcoma support tissue bone, muscle
• Glioma nerve tissue brain, eyes
• Leukemia, lymphoma white blood cells
• Cancer cells ignore cell cycle controls
• - some make their own growth factor
• - grow extra blood vessels to feed themselves
• - divide randomly (no cycle) immortal