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 shown but 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… What are the major events in Meiosis I?… Prophase I: Metaphase I: Anaphase I: Telophase 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: After S1 phase (Sister chromatids) Copy of Chromosome (doubling the DNA) A chromosome before the S1 phase Original Chromosome

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