Meiosis
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Transcript of Meiosis
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Meiosis
Sex cell production
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Meiosis - Sex Cell Reproduction
• Requires two parents
• Parent cells produce sex cells– Male (sperm)– Females (egg)
• Sex cells have ½ the number of chromosomes– Humans have 46
chromosomes– So human sex cells have how
many chromosomes?• 23
• When sex cells combine the offspring will have a full set of chromosomes
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Sexual Reproduction
• Advantages of sexual reproduction– Chromosomes from 2 parents– offspring are different than
the parent– Offspring are likely more
adaptable
• Different from asexual reproduction which
ALWAYS produces offspring that are the SAME.
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Homologous Chromosomes• Chromosomes that carry
the same set of instructions.
• One from mother and one from father• Remember – these replicate during interphase!
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Meiosi
s
• Produces sex cells and
• Parent cells divide twice producing4 daughter cells
• Daughter cells (sex cells) have ½ the number of chromosomes as the parent cell
Growing quadruplets
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Meiosis I Contains all the steps of
mitosisIs like mitosis except…– Homologous
chromosomes pair up– Sister chromatids don’t
separate– Produces TWO cells
Meiosis occurs in two steps…..
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Meiosis II Contains all steps of
mitosisIs like mitosis except:• No DNA replication• 4 daughter cells
with ½ number of chromosomes as parent
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• Diploid (2n) – full set of chromosomes–Parent cell
• Haploid (n) – half a set of chromosomes
–Daughter cells
Additional Vocabulary
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Sex Cell
s
Sperm Cells
Egg Cells
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http://www.mwit.ac.th/~bio/assets/meiosis%5B1%5D.swf
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Mitosis & Meiosis on the Table• Objective: Discover critical differences between mitosis and
meiosis, and the main functions of meiosis.
• Assumptions: copy from handout• Table: Distinguishing features• Summary: Copy from handout
• Questions: 1. What are the 2 main functions of meiosis?2. If you were to model an organism with six chromosomes how
many more pipe cleaners will you need? Will you need to use a third color? Why or why not?
3. Adder’s fern has 1,400 chromosomes. How many chromosomes do its sex cells have?