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Biology 3
Ch 6 Cell Division
Dr. Terence Lee
Telomeres
� The telomere is like a protective cap at the end of the DNA.
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Three Types of Cell Division
• Asexual Reproduction
– Binary fission and mitosis
are the primary means of
reproduction in single cell
organisms.
• Sexual Reproduction
– Combining of genetic information from two parents.
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The Cell Cycle
The Cell Cycle
• Interphase
– The longest phase
– Also called the growth phase
– Prepares for next cell division.
• Mitosis
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Mitosis
• Prophase
1. Chromosomes condense
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Sister Chromatids
Early Prophase
Prophase
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Metaphase
Anaphase
1. The chromosome breaks in
half
2. Each sister chromatid is now a
new daughter chromosome.
Telophase
1. Spindle fibers disassemble
2. Nuclear membrane re-forms
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Cytokinesis
• Process during which …
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Cell Division and Sexual
Reproduction
• Why sexual reproduction when asexual reproduction
(mitosis) gets the job done?
Cell Division and Sexual
Reproduction
Humans have two sets of chromosomes
Cell Division and Sexual
Reproduction
• Haploid
• Diploid
• Gametes
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Meiosis I
Overview
Meiosis I
• Prophase I
1. Chromosomes condense
2. Spindle and spindle fibers form
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Meiosis I
• Metaphase I
Meiosis I
• Anaphase I
1. Homologous chromosomes
separate from each other
2. Chromosomes move toward
cell’s poles
Meiosis I
• Telophase I
1. Spindle fibers disassemble
2. Chromosomes uncoil
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Meiosis I
Review
Meiosis II
• Prophase II
1. Chromosomes condense
2. Spindle and spindle fibers
form
Meiosis II
• Metaphase II
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Meiosis II
• Anaphase II
– Chromatids separate as
chromosomes begin to
move to cell’s poles
Meiosis II
• Telophase II
1. Nuclear membrane re-forms
2. Chromosomes uncoil
Review
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Sex Determination
• Autosomes
– Non-sex chromosomes (1-22)
• Sex Chromosomes
– XX and XY (23)
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6.16 The sex of the offspring is determined in a variety of ways
in other species.
The sex of the offspring is determined in a variety of ways
in other species.
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The sex of the offspring is determined in a variety of ways
in other species.
Chromosome Number
• Normal person has 23 pairs of chromosomes
• Downs Syndrome or
trisomy 21 is caused by
nondisjunction