UNIT 7: Cell Division
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Transcript of UNIT 7: Cell Division
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UNIT 7: Cell Division
BIG IDEA: Cell division is the process in the body to create
more cells and gametes
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Chromosome Structure• Inside your nucleus are 3 billion
nucleotides of DNA• In order to fit it is coiled and packed
into a complicated but organized structure
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Chromosome Structure• Histones-Proteins that DNA are wrapped around
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Chromosome Structure• Chromati
n-Less tightly coiled DNA wrapped around a histone
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Chromosomes• Rod shaped structures made up of
DNA and histones• Two identical halves are called
chromatids• Point holding together the
chromatids is called a centromere
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Chromosomes• Structure in cells
that undergo division and that contain hereditary information of the organism
• In mitosis the chromosomes that undergo cellular division are called autosomes
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Chromosomes• Draw a
chromosome and label the centromere and the chromatids
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How many chromosomes are present in an autosomal cell?
• 23 pairs or 46 chromosomes
• Refers to DIPLOID: meaning that a cell possesses 2 complete sets of chromosomes
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Why are there two sets of chromosomes?
– 1 set is from your mother and 1 set is from your father
– This leads to genetic variation because genetic information on chromosomes from your parents can be different
• Example: both chromosomes can code for eye color except one can be for blue eyes and one for green eyes
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Blonde Hair Black Hair
Genetic Variation
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Why is genetic variation beneficial?
• Causes a diverse collection of genes
• Increase in survival
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MITOSIS• Cell division that produces two
identical diploid daughter cells• Every body cell has a life span called
the cell cycle so cells must divide to replace themselves
• Cells also divide in order for organisms to grow
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CELL CYCLE• Cycle that a cell goes through in order to make new cells
• If an organism is unicellular, than a new organism is created via the cell cycle
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Asexual Reproduction• Reproduction with only one parent
• offspring are identical to parents
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Sexual Reproduction• Requires 2 parents• New individual is produced by
the union of the nuclei of two specialized cells (sperm & egg)
• We all start off as a single cell-the cell cycle and division made you what you are today
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Cell Cycle Consists of Two Parts:
• Mitosis:– Division of the
nucleus to form two identical nuclei
– REMEMBER: Hereditary material is found in the nucleus
• Cytokinesis–Division of the
cytoplasm of the cell after mitosis
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INTERPHASE
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Interphase• Stage when a cell
is between mitotic cycles:
A. G1- cell growsB. S- DNA replicationC. G2- Organelle replication
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MITOSIS
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Prophase• Chromosome
become visible• Centrioles
move to opposite poles of the cells
• Microtubules form spindles
• Spindle fibers become attached to centromeres
• Nuclear membrane disappears
• Nucleolus disappears
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Prophase:
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Metaphase• Chromosomes
attach to the microtubule spindles
• Chromosomes line up on the equator of the cell
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Anaphase• Centromeres
double• Chromosomes(sis
ter chromatids) move to opposite poles
• Division (cleavage furrow) appears
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Telophase• Begins when chromosomes reach the poles
• Chromosome uncoil and become invisible
• Spindle disappears• Nuclear membrane forms• Nucleioli reappears
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Telophase
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Cytokinesis in Animal Cells• Begins during late anaphase
• Cytoplasm is pinched off by cell membrane
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Mitosis & Cytokinesis in Plant Cells
• Main events are the same• Plants do not have centrioles or
asters• Cytokinesis cannot occur by
pinching off of membrane a cell plate forms between the new cells during anaphase or telophase
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Cytokinesis
End with two identical daughter cells
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Cells that divide rapidly• Plants • Animals
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Cells that seldom or never divide
• Xylem (part of a plant)
• Nerve Cells• Muscle Cells
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Meiosis• Remember-mitosis is cell division in
autosomes (all cells except sex cells)
• Meiosis is the creation of haploid sex cells for reproduction
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What is the function of a haploid cell?Used in sexual
reproduction
EX: sperm for males & egg for females
During fertilization haploid sperm and haploid egg combine to form a diploid cell
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How does meiosis begin?• Once diploid cells in reproductive
organs have replicated DNA and they are no longer in interphase meiosis starts
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(i.e. Prophase I and Prophase II)
Stages of Meiosis: Same as mitosis EXCEPT there are two for each stage
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Prophase I • Chromosome condense from
chromatin• Nuclear Membrane Disappears• Spindle fibers develop on which
chromosomes group together• Homologous chromosomoes align
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Prophase I continued• The pairs of chromosomes are called
a tetrad and the pairing up is called synapsis
• Chromatids may break off and attach to adjacent chromatids-called crossing over.
• Exchange of genetic material between parental chromosomes creates genetic recombination
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Metaphase I• Duplicated chromosomes line up in
the middle of the cell.
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Anaphase I• Chromosomes move to opposite poles
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Telophase I• One set of each chromosome ends up
in each new nucleus and the cytoplasm divides
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Now these two cells will go through the phases again
At this point we have two DIFFERENT diploid cells
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Prophase II• Spindle fibers form• Chromosomes move toward the
middle of the spindle
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Metaphase II• Spindle fibers attach to centromere of
chromosomes and chromosomes are in the middle of the cell.
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Anaphase II• Chromosomes separate and move
toward opposite ends of the cells
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Telophase II• Daughter cells divide to form 4 haploid
cells• Chromosomes return to their
interphase or “resting” form
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At the end of meiosis…• Result in 4 cells
• Either sperm or egg cells
• Each cell possesses half the number of chromosomes of the parent (or 23 chromosomes)
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Why is the number of chromosomes reduced by half?
• Cells have divided two times but DNA was only replicated once
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Review: Diploid cells Haploid Cells
In meiosis, haploid daughter cells are created from diploid parent cells
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Chromosome Errors in Cell Division
• Deletion-loss of a piece of a chromosome
• Inversion-A chromosomal segment breaks off, flips around and reattaches
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Chromosome Errors in Cell Division
• Translocation-a piece of a chromosome breaks off and reattaches to a nonhomologous chromosome
• Nondisjunction-a chromosome does not separate from its homologue during meiosis