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Cellular Division
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Two meiotic divisions --- Meiosis I and Meiosis II

Called Reduction- division

Original cell is diploid (2n)

Four daughter cells produced that are monoploid (1n)

Slide 68

Facts About Meiosis

Facts About Meiosis

Daughter cells contain half the number of chromosomes as the original cell

Produces gametes (eggs & sperm)

Occurs in the testes in males (Spermatogenesis)

Occurs in the ovaries in females (Oogenesis)

Slide 69

Start with 46 double stranded chromosomes (2n)

Start with 46 double stranded chromosomes (2n)

After 1 division - 23 double stranded chromosomes (n)

After 2nd division - 23 single stranded chromosomes (n)

Occurs in our germ cells that produce gametes

More Meiosis Facts

Slide 70

Why Do we Need Meiosis?

Why Do we Need Meiosis?

It is the fundamental basis of sexual reproduction

Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote

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Fertilization – “Putting it all together”

Fertilization – “Putting it all together”

1n =3

2n = 6

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Replication of Chromosomes

Replication of Chromosomes

Replication is the process of duplicating a chromosome

Occurs prior to division

Replicated copies are called sister chromatids

Held together at centromere

Occurs in Interphase

Slide 73

A Replicated Chromosome

A Replicated Chromosome

Gene X

Homologs separate in meiosis I and therefore different alleles separate.

Slide 74

Meiosis Forms Haploid Gametes

Meiosis Forms Haploid Gametes

Meiosis must reduce the chromosome number by half

Fertilization then restores the 2n number

The right number!

Slide 75

Meiosis: Two Part Cell Division

Meiosis: Two Part Cell Division

Homologs

separate

Sister

chromatids

separate

Diploid

Diploid

Haploid

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Meiosis I: Reduction Division

Meiosis I: Reduction Division

Early Prophase I

(Chromosome number doubled)

Late Prophase I

Metaphase I

Anaphase I

Telophase I (diploid)

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Prophase I

Prophase I

Early prophase

Homologs pair.

Crossing over occurs.

Late prophase

Chromosomes condense.

Spindle forms.

Nuclear envelope fragments.

Slide 78

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