Cellular Reproduction:

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Chapter 8

• Cellular Reproduction
• Cells from Cells

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Reproduction

• Usually thought to be the birth of a new organism
  but in Biology it is the creation of new cells as
  well as the formation of a zygote
• Our cells must be continually dividing to
  maintain our 60 trillion cells

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Functions of Cell Division

• Divide to maintain the organism
• Growth of the organism by having more cells
• Cell division is to make 2 daughter cells from a
  parent cell
• need to duplicate chromosomes (DNA) so each cell
  gets a complete set

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Simple Cell Division

• Cells are identical to the parent cell
• Asexual reproduction chromosomes from a single
  parent and all offspring have the same genes
  caused by mitosis

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Sexual Reproduction

• Requires an egg and a sperm
• made thru the process of meiosis
• only in the reproductive tissue of ovary and
  testis
• have only half the number of chromosomes (1 of
  each type)
• Both mitosis and meiosis are involved in sexually
  reproduced organisms

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Chromosomes

• Genes are found on chromosomes in the nucleus,
  mitochondria and chloroplasts
• Organisms have different numbers of chromosomes
• even number providing no genetic abnormality
• 1 set from mom and 1 from dad

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Chromatin

• Loosely packed DNA wrapped around a protein
  called a histone
• Chromosomes not seen in light microscope until
  cell is getting ready to divide

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DNA Packaging

• DNA wrapped around a histone protein particle to
  make a nucleosome bead on a string look
• Helps to package DNA into a nucleus
• Will eventually coil up into a chromosome

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Chromosome Structure

• Chromosome is duplicated to form an X shape made
  up of 2 identical sister chromatids
• identical DNA sequence
• joined at the centromere
• Sister chromatids will separate during cell
  division then called chromosome
• one into each new daughter cell

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Cell Cycle

• Process that regulates cell division
• time varies for different cells
• 90 time spent in interphase as the cell
  prepares for cell division
• consists of 2 growth periods, DNA replication and
  mitosis

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Cell Division

• Occurs in the M phase of the cell cycle
• 2 overlapping processes
• Mitosis nucleus divides into 2 daughter nuclei
  with full set of chromosomes
• very few mistakes in process
• Cytokinesis cell divides into 2 daughter cells
• Each new cell is identical to the parent
• Unique to eukaryotic cells, bacteria do it
  differently

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Mitosis

• Sticking changes are going on in the cell
• 4 phases that are a continuum
• Chromosomes are the most important part of this
  process because we need to equally distribute
  them to the new cells
• Mitotic spindle group of microtubules that
  separate the chromatids, arise in the centriole

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• Interphase normal cell, no evidence of
  chromosomes
• Prophase mitotic spindle forms, nuclear
  membrane breaks down and chromatin condenses

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• Metaphase chromosomes line up at metaphase
  plate equator of cell
• Anaphase mitotic spindle pulls chromosomes to
  each end of cell
• Telophase chromosomes de-condense and nuclear
  membrane reforms

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Cytokinesis Animal Cell

• Division of cytoplasm
• Cleavage furrow is made of a contractile ring of
  microfilaments to pinch the cell into new
  daughter cells
• Starts in anaphase and completes at end of
  telophase

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Cytokinesis Plant Cell

• No cleavage furrow but form a cell plate
  consisting of cell wall material
• moves outward to join with the cell wall and
  complete cell division

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Cancer

• Cell grows out of control no response to the
  cell cycle control mechanism
• stop and go ahead signals
• No go ahead signal will force a cell into G0
  meaning no cell division
• nerve and muscle cells

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2 Types of Tumors

• Benign abnormal cell growth but does not invade
  adjacent tissue
• Malignant spreads to adjacent tissue and spread
  to other parts of body (metastasis)

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Types of Cancer

• Named based on the origination site
• carcinomas external and internal linings of
  body cavities or skin
• sarcomas tissues that support the body such as
  bone and muscle
• leukemias blood cells and bone marrow
• lymphomas lymph nodes

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Cancer Treatment

• Dependent on the type and location of cancer will
  dictate the type of treatment
• Treatments include
• surgery
• radiation therapy high-energy radiation,
  disrupts cell division by damaging the DNA
• chemotherapy use drugs to disrupt cell division
  usually by disrupting mitotic spindle
• taxol Pacific Yew tree
• vinblastine periwinkle plant
• Decrease need for this by quit smoking, exercise
  regularly, avoid excessive sun exposure and do
  self exams --- EARLY DETECTION

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Meiosis

• Basis of sexual reproduction
• Get a unique set of offspring because the genes
  come from 2 parents rather than 1 in asexual
  reproduction
• Egg and sperm come together in fertilization

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Homologous Chromosomes

• Cells of an individual have the same number of
  chromosomes
• somatic cells all cells but gametes
• humans have 46
• Karyotype is a picture of the chromosomes from an
  individual
• 22 matching sets called autosomes
• 1 set called sex chromosomes

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Life Cycle

• Adult of 1 generation to adult of the next
  generation
• Somatic cells are diploid have 2n chromosomes
• Gametes are haploid have 1n chromosomes so that
  zygote is diploid
• All sexual life cycles fluctuate between diploid
  and haploid stages

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Meiosis

• Process that makes the haploid cells or gametes
• Similar to mitosis but 2 special features
• halving the number of chromosomes 2 rounds of
  cell division, meiosis I and II
• exchange of genetic material swap parts of
  chromosomes in a process called crossing over

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Homologous Chromosomes

• 2 near identical copies of each chromosome 1
  from the mother and 1 from the father
• Sister chromatids identical copies of
  chromosome made during DNA replication

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Meiosis I

• Prophase I crossing over occurs
• Metaphase I homologous pairs line up as a
  tetrad
• Anaphase I and Telophase I are same as mitosis
  except that sister chromatids are separated and
  have only 23 chromosomes is each new daughter cell

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Meiosis II

• Much more similar to mitosis but with half the
  chromosomes
• Final cells are either sperm or egg and are
  haploid

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Important Things

• DNA is duplicated only once during S phase
• Mitosis and meiosis II are the same with the
  exception of the number of chromosomes
• Metaphase I has mom and dad chromosomes pairing
  up
• Prophase I has crossing-over occurring

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Genetic Variation

• Offspring from sexual reproduction are different
  from parents and other offspring
• Happens because of independent assortment
• in humans about 8 million combinations of
  chromosome distribution in egg and sperm which
  means about 16 trillion possible combinations in
  zygote

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Independent Assortment
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Crossing-Over

• Exchange corresponding segments of chromosomes
  because of close proximity during prophase I of
  meiosis I
• Form a chiasma between chromosomes and make a
  genetic recombinant
• Can see multiple cross-overs in each tetrad

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Errors

• Usually errors result in faulty mitotic spindles
  that result in non-disjunction
• chromosome fails to separate during Anaphase I or
  II so the egg or sperm does not get a full set of
  chromosomes

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Consequences Of Non-Disjunction

• End up with a zygote with an extra chromosome
• Mitosis will pass this one to all somatic cells
• See increase in this as women age

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Down Syndrome

• 3 copies of chromosome 21 usually results in a
  live birth with a collection of symptoms
• called trisomy 21
• Other trisomies are usually much more traumatic
  in terms of development and end in miscarriage

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Increase in Non-Disjunction

• As women age there is an increase in Down
  Syndrome cases
• 1 in 2000 before 30
• 1 in 80 in early 30s
• even higher after 40

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Non-Disjunction in Sex Chromosomes

• These are not nearly as dramatic as in autosomal
  chromosomes
• Can tolerate excess X chromosomes because we will
  just shut them off
• 1 Y is enough to develop maleness regardless of
  the number of Xs
• XO only instance where 45 chromosomes not fatal
  and other than sterility, decreased girlness
  there isnt much wrong