I. The Cell Cycle
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I. The Cell Cycle
• There are three stages to the cell cycle:1. Interphase
-G1 (growth)-S (DNA Replication)-G2 (growth and addition of organelles)
2. Mitosis-Prophase-Metaphase-Anaphase-Telophase
3. Cytokinesis
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I. The Cell Cycle• The Cell cycle
represents the time it takes for a cell to grow, reproduce, and divide
• Some cells go through the Cell Cycle much quicker than others
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A. Interphase
• Interphase is the longest part of the cell’s life
• Some cells (muscle and nerve cells) remain in interphase permanenty
• During interphase, the cell experiences growth, replication of DNA, and duplication of the organelles
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B. Mitosis
• Mitosis is the division of the cell’s nucleus
• It occurs in four phases:• Prophase• Metaphase• Anaphase• Telophase
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1. Prophase• The chromatin changes
into a more mature form:
chromatin chromatid chromosomes
• The nuclear membrane will disappear
• The centrioles and spindle fibers will appear
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2. Metaphase
• Chromosomes will line-up at the cell’s equator
(move to the middle)
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3. Anaphase• The spindle fibers
pull the chromosomes apart
chromosomes chromatid
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4. Telophase• The chromatid
unwind into chromatin
• The centrioles and spindle fibers disappear
• The nuclear membrane reappears
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Telophase in an animal cell:
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C. Cytokinesis
• Cytokinesis is the division of the cell membrane and cytoplasm
• In plant cells, a cell plate forms in between the new cells. The cell plate eventually forms a cell wall.
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C. CytokinesisC. Cytokinesis
In plant cells a cell plate forms in between In plant cells a cell plate forms in between the new cells and will become the cell the new cells and will become the cell membrane. A cell wall then forms around membrane. A cell wall then forms around the cells.the cells.
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III. Mistakes in Mitosis
• Cancer is a disease in which cells grow and divide uncontrollably, damaging parts of the body around them.
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IV. Meiosis
• Meiosis is the formation of sex cells or gametes.
• Sex cells contain half the number of chromosomes that normal body cells have• normal cells in humans have 46• sex cells in humans have 23
• When two sex cells combine they form a zygote.
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IV. Meiosis
• Meiosis is basically mitosis twice without replication after the initial mitosis.
• Meiosis has two divisions:• the first division reduces the number of
chromosomes (from 46 to 23)• the second division makes another copy of
the cell
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IV. Meiosis
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A. The Results of Meiosis
• In Females – one egg and three polar bodies form
• In Males – four sperm cells form
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V. Genetic Inheritance
• The male sperm cell and the female egg cell join together to form a zygote
• The sperm contributes 23 chromosome and the egg contributes 23 SIMILAR chromosomes
• These similar chromosomes pair up and form homologous chromosomes
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A. Karyotype
• A karyotype is a picture of one’s chromosomes
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B. Homologous Chromosomes
• These chromosomes are sorted into similar pairs called homologous chromosomes
• The 23rd pair tells us if it is male or female• Male XY• Female XX
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VI. Mistakes in Meiosis
• Nondisjunction is one of the most common errors that occurs in meiosis
• In nondisjunction, some chromosomes fail to split apart during anaphase
• This causes the resulting cells to have too many or too few chromosomes
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VI. Mistakes in Meiosis
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A. Trisomy 21
• Trisomy 21 occurs when a person has an extra 21st chromosome.
• Some characteristics include slow mental development, heart problems, small head, a distinct crease in the palm of the hand
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One day old infant