THE CELLULAR BASIS OF
REPRODUCTION AND INHERITANCE
Chapter 8
When demands are too high The Result: Cell Division
Cell Division
Ratio of surface area to volume cannot get too large because…Demands on DNA = “info crisis”Nutrient and waste movement = “traffic
jams”
Cell Division in Our Bodies Brain cell - doesn’t divide in a lifetime
RBC’s - 120 days
Skin cells - 35 days
Stomach cell - 2 days
Bacteria cell - 20 to 30 minutes
DNA PackagingSimple to complex Double helix Chromatin: DNA
and histones (protein)
Supercoils Chromosomes:
tightest packaged DNA
Chromosomes Genetic information in eukaryotic cells is
organized into chromosomes. Chromosomes are only visible (with a light
microscope) during cell division, it is then that they pack tightly into a dense visible structure.
Chromosomes are copied before division Copied chromosomes consist of two
identical “sister” chromatids held together by an area called the centromere.
Parts of a Homologous Pair of Chromosomes
Centromere
Chromosome
Chromatid
Homologous Chromosomes
Cell Division “All cells come from pre-existing cells” Prokaryotic cell division: binary fission
Eukaryotic cell division: mitosis and meiosis
Cell Division Why do cells divide?
To repair damaged or old cellsSo the organism can get larger (grow)
The Cell Cycle Describes the Life Cycle of a Cell Every cell
follows a specific sequence of steps, just like a human goes through stages of life.
THE MAJOR AND MINOR STAGES OF THE CELL CYCLE
Interphase: Cell growth and DNA replicationGap 1SynthesisGap 2
The Mitotic Phase:Mitosis: the division of the nucleus
○ Prophase○ Metaphase○ Anaphase○ Telophase
Cytokinesis: the division of the cytoplasm.
Interphase (Stage 1)
Gap 1 (G1) – Cell grows, preps for DNA replication
Synthesis phase (S-phase) – DNA is replicated
Gap 2 (G2) – Cell grows, preps for mitosis
3 Sub-Stages of Interphase
Mitosis (Stage 2 – part of the mitotic phase)
Prophase Metaphase Anaphase Telophase PMAT!
4 Sub-Stages of Mitosis
Mitosis: The division of the nucleus
ProphaseChromosomes
become visible Centrioles separate
and move to opposite ends of the cell
The spindle (a structure that helps to separate the chromosomes) forms
Nucleolus disappears and nuclear envelope breaks down
MetaphaseMicrotubles attach
to the centromeres to move the chromosomes
Chromosomes line up in the center of the cell
Mitosis: The division of the nucleus
AnaphaseCentromeres that join
sister chromatids split in half
Sister chromatids split and become individual chromosomes
Chromosomes move to opposite poles of the cell
TelophaseChromosomes
begin to disperse and are less visible
Nuclear envelopes begin to reform around each cluster of chromosomes
The spindle fibers dissolve
MitosisAt the end of
InterphaseProphase Metaphase Anaphase Telophase
Blood lilly
Mitosis
At
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Inte
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ase
Pro
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Meta
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An
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Telo
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Cytokinesis (Stage 2 – part of the mitotic phase)
The result of Mitosis is the formation of two nuclei each with duplicate sets of chromosomes formed within the cytoplasm of a single cell.
Cytokinesis separates the cytoplasm of the cell into two.During cytokinesis in plant cell a cell
plate forms between the nucleiDuring cytokinesis in animals a cleavage
furrow forms pinching the two cells apart
Do You Know the Stages of Mitosis?
CYTOKIN
ESIS
PROPHASE
ANAPHASE
ANAPHASE
INTE
RPHASE
MET
APHASE
TELO
PHASE
Controls on cell division
Anchorage dependence – cells must be in contact with a solid surface to divide.
Density dependent inhibition – when cells are touching other cells they don’t usually divide
Growth factors are proteins that tell cells to divide
Growth factors control the cell cycle
Cells do not usually divide unless they get a chemical signal.
The cell cycle control system is a set of molecules that help to trigger and coordinate important steps in the cell cycle.
Checkpoints are critical control points in the cycle when cells will either stop or go forward in the cycle.
Proteins that control the steps in the cell cycle are called cyclins.
Controls on Cell Division Most cells are in interphase Checkpoints for division:
Is DNA fully replicated?Is the DNA damaged?Are there enough nutrients to support cell
growth Proto-oncogenes – start cell division Tumor-Suppressor Genes – stop cell
division
Mutations in both types of
genes can lead to cancer
Controls on Cell Division
Example Tumor suppressor gene:p53 stops cell division and induces
apoptosis in abnormal cells (cells with damaged DNA)○ Apoptosis – cell suicide (pre-programmed
death)
Example proto-oncogene:Ki-ras – when mutated can lead to
increased risk of lung, ovarian, colon and pancreatic cancer
Apoptosis Video
Uncontrolled Cell Growth Cancer is a disease caused by cells that
do not respond to the signals that regulate growth.
According to the American Cancer Society:As of 2008 in the USA a man has a 1 in 2
chance of developing cancer in his lifetime and a woman has a 1 in 3 chance of developing cancer in her lifetime
Cancer accounts for 1 in 4 deaths in the U.S. each year.
Cancer occurs when extra cells form a mass or a tumorBenign tumor remain within the mass (non-
cancerous)Malignant tumor cells invade and destroy healthy
tissues elsewhere in the body (cancerous)
Types of Cancer Carcinoma - affects skin cells
(most common) Sarcoma - affects muscle,
bone, cartilage, fat or connective tissues.
Leukemia - affects white blood cells or their precursors (begins in bone marrow)
Lymphoma - affects bone marrow cells/lymphatic system (solid tumors)
Malignant Tumor
Normal Cells
Metastasized Tumor
What Causes Cancer?
Gene changes due to: diet – lack of antioxidants tobacco use exposure to radiation exposure to chemicals Inherited genes (p53 or Ki-ras don’t work)
Immune System Failure
Carcinogens
Allergic reactions, swelling, itching also flu like symptoms, greatest concern is extreme allergic reactions.
Biological Therapy:Elicits a response from your immune system (helps immune system fight cancerous cells)
Weakening of the bones can also effect sex characteristics
Hormone Therapy:Blocks hormones that cancer needs to grow
Similar to radiation therapyChemotherapy: Chemicals target cancer cells given 2 or more at a time
Can injure or kill healthy cellsRadiation Therapy:Damages cancer cell’s DNA, cells won’t reproduce
Restricted to a few types of cancer, may not get all cells, damages organs.
Surgery: physically remove tumor
Side EffectsTreatment
Cancer Among Men
The three most common cancers among men include:Prostate cancerLung cancerColorectal cancer
The leading causes of cancer death among men are:Lung cancerProstate cancerLiver cancer
Cancer Among Women
The three most common cancers among women include:Breast cancerLung cancerColorectal cancer
The leading causes of cancer death among women are:Lung cancerBreast cancerColorectal cancer
Meiosis and Crossing Over
Mitosis is cell division to replace dead cells or allow an organism to grow.
Meiosis as a specialized type of cell division that occurs only in the reproductive organs, to create reproductive cells.
Chromosomes in Somatic Cells are Matched in Homologous Pairs
Somatic cell: a body cellEx. skin cell, bone cell, etc.Contain 46 chromosomes
(diploid meaning 2 copies)○ Pairs 1-22 are called autosomes○ Pair 23 (X and Y) are sex
chromosomesThere are 23 types of
chromosomes which exist as pairs called homologus chromosomes
Homologous chromosomes
Carry the same genes at the same locations (called loci)
Genes may be different versionsEx. gene is eye color
versions of those genes include: brown, blue, grey, hazel, green
Gametes have a single set of chromosomes
Gametes are sex cellsSperm cell and egg cellGametes have only 1 copy
of each type of chromosome (called haploid – 1n)
When two gamete cells combine a diploid cell (2n) called a zygote is created.
Meiosis reduces the chromosome number from diploid to haploid
Meiosis Occurs only in sex cellsTwo divisions
○ Meiosis I○ Meiosis II
Creates haploid cells from diploid cellsCreates genetic diversity through:
○Crossing over (Prophase I)
○ Independent assortment (Metaphase I)
PROPHASE I
METAPHASE I
ANAPHASE I TELOPHASE I
STEPS OF MEIOSISMEIOSIS I
STEPS OF MEIOSIS: MEIOSIS I
Homologous chromosomes
sister chromatids sister chromatidsTetrad
Maternal Chromosom
e
Paternal Chromosom
e
PROPHASE I: Grouping of tetrads and crossing over
Non-sister chromatids Crossing
over
Crossing over: homologous chromosomes exchange genetic material
STEPS OF MEIOSIS: MEIOSIS I
PROPHASE I: Grouping of tetrads and crossing over
Crossing over contributes to genetic diversity
centriolesspindle fiber
STEPS OF MEIOSIS: MEIOSIS IPROPHASE I: Grouping of tetrads and
crossing over
OR
Independent Assortment: tetrads line up randomly during Metaphase I
Contributes to genetic diversity
STEPS OF MEIOSIS: MEIOSIS I
METAPHASE I: Independent assortment
ANAPHASE I: Homologous chromosomes separate
Tetrads split Homologous chromosomes move to opposite ends
of cell Sister chromatids stay together (not like mitosis)
STEPS OF MEIOSIS: MEIOSIS I
2 new cells each with haploid set of chromosomes
In human sex cells 23 chromosomes
STEPS OF MEIOSIS: MEIOSIS I
TELOPHASE I/CYTOKINESIS I: Homologous chromosomes separate
MEIOSIS I – recap!
PROPHASE I
METAPHASE I
ANAPHASE I TELOPHASE I
MEIOSIS I – recap!Q: What is the purpose of Meiosis I?
A: To decrease the # of chromosomes by 1/2
Q: What 2 features of Meiosis I increase the diversity of the daughter cells?
A: Crossing Over & Independent Assortment
PROPHASE II METAPHASE II ANAPHASE IITELOPHASE II
MEIOSIS II
STEPS OF MEIOSIS: MEIOSIS II
Happens immediately after cytokinesis I – interphase does not happen!
Meiosis II stages: prophase IImetaphase IIanaphase II telophase II
Meiosis II is nearly identical to Mitosis
PROPHASE II METAPHASE IIANAPHASE II TELOPHASE II
MEIOSIS II
Summary of MEIOSIS
The entire process of meiosis results in
four haploid daughter cells.
gametes = sperm or egg
Karyotypes
A karyotype is a photographic inventory of an individual’s chromosomes
White blood cells are made to go through mitosis. Cells are treated to stop cells during metaphase of mitosis and a picture is taken of the cell.
Karyotypes are used to determine gender and also identify chromosomal abnormalities.
Development of a Karyotype
Is it a boy or girl?
Chromosomal Abnormalities
Occasionally chromosomes do not separate properly during meiosis, these mistakes are called nondisjunction
This can result in too many or too few chromosomes
Most cases result in miscarriage. Some types of nondisjunction result in specific
syndromes
Chromosomal Abnormalities Down syndrome =
trisomy 21 (three copies of chromosome 21)Effects 1 out of every
700 childrenSymptoms:
○ Round face○ Short stature○ Heart defects
Chromosomal Abnormalities Klinefelter
syndrome = XXYMales born
are sterileUsually
normal intelligence
Chromosomal Abnormalities Turner
syndromeFemales lack a
second X chromosome.
Short statureWebbed neckSterile
Alterations of chromosomes can cause birth defects and cancer
Deletion – section of chromosome is deleted
Duplication – section of chromosome is copied twice
Inversion – section of chromosome is out of order
Translocation – non-homologous chromosomes cross over