Meiosis Guided Notes

Ramshaw – Biology

Interphase…• Interphase happens at the start of

_____________ as well as mitosis.

• Prior to prophase I, the cell goes through the G1, S, and G2 phases of ________________.

Prophase I(chapter 10)

• DNA coils into ___________ chromosomes, spindle fibers appear, nucleus disappears.

• Every chromosome is paired up next to its ______________ (the chromosome that is the same size and shape).

• This is called _____________ and does not occur in mitosis.

Prophase I (cont.)• Each pair of homologous

chromosomes is called a ______________.

• When chromosomes line up next to each other, “____________ ______” occurs and they exchange pieces of DNA.

• This is called _________ recombination.

Crossing over

Only one cross over is shownbut many occur per pair.

So why is Crossing Over SO important?????

• Reasons why:

Review of Key Terms• Homologue (Homologous Chromosomes):

• Synapsis

• Tetrad

• Crossing Over

Metaphase I• _____________ line up in the

center of the cell next to each other.

• Spindle fibers from one centriole attach to the centromere of one _________ chromosome then spindle fibers from the opposite centriole attach to the other homologous _____________.

Anaphase I• Each homologous

chromosome moves to the _____________ pole.

• This __________ separation of homologous chromosomes is called ________________ assortment. – It separates the chromosomes

you inherited from your mom and dad and creates new combinations of ________ on each chromosome!

Telophase I

• Chromosomes reach the opposite ends of the ______, new nuclei form in each new cell, and spindle fibers __________.

• The new cells are ___________!

To review…

• Prophase I:

• Metaphase I:

• Anaphase I:

• Telophase I:

What are the major events in Meiosis I?…

NO INTERPHASE HERE

• There is no interphase between _____________ 1 and ____________ 2. This is very important because there is no S phase!!! (no doubling of the ________!!!)

Start of Meiosis II

Prophase II– Centrioles form and move

toward the __________ – The nuclear membrane

________________

Metaphase II

• __________ fibers attach from the centrioles to the centromeres

• The __________ chromatids line up along the cell equator

Anaphase II

• The centromeres __________ and sister chromatids separate 

• The cell starts to ______ apart

Telophase II – Cytokinesis

• The cell pulls _____________ apart – forming new nuclei, one in each cell

• Cytokinesis reaches completion, creating ___ haploid ____________ cells

These 4 haploid cells then create:• ______________!• If the organism going through meiosis is a

female, only ___ of the cells becomes the egg, the others become “_______ Bodies” and are dissolved by the body. This process of making an egg is called __________________.

• If the organism going through meiosis is a male, _____ __ cells become spermatids which mature in to sperm. This is called _______________________.

Major events in Meiosis!• The cell starts out by doubling the _____

in Interphase:

A chromosome beforethe S1 phase

Original Chromosome

Copy of Chromosome(doubling the DNA)

After S1 phase(Sister chromatids)

After Interphase is…

• Prophase I

• _____________ and crossing over occur

• Lets draw that out!

Then comes:

• Metaphase I – Homologous chromosomes line up in the _________ of the cell next to each other.

• Anaphase I – The __________ are pulled apart, one to each side of the cell

• Telophase I – Two ___________ cells are formed

Then the second part - Meiosis II

• Prophase II – Nucleus _______________

• Metaphase II – Chromosomes line up _________ file down the middle of the cell

• Anaphase II – Sister chromatids are pulled ___________ towards opposite ends of the cell

• Telophase II – 4 __________ cells are formed