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11.4 Meiosis

Meiosis
by

Lori Richardson

on 8 January 2014

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Transcript of 11.4 Meiosis

Today's Objectives At the end of today's lesson students should:

-Be able to compare and contrast mitosis and meiosis.
-Be able to demonstrate how crossing-over leads to genetic variation. Chromosome number We have a total of 46 chromosomes in our cells.
23 come from mom and 23 come from dad.

Homologous chromosomes are two identical chromosomes that come from different parents. They carry the same genes but specify slightly different traits. Homologous
Chromosomes

1 Paternal
1 Maternal Chromosome Number A cell that contains both sets of homologous chromosomes is said to be diploid, which means "two sets"
-Somatic cells are diploid.

A cell that contains only a single set of chromosomes is said to be haploid, which means "one set"
-Sex cells (gametes) are haploid. Meiosis Meiosis has two divisions called Meiosis 1 and Meiosis 2.
Meiosis 1: Homologous Chromosomes Separate
Meiosis 2: Sister Chromatids Separate

The 3 main differences in the cell division
of mitosis and meiosis are:

-Formation of a Tetrad
-Crossing-over
-Two Divisions vs. One Division Formation of a Tetrad In Prophase of Meiosis 1 each chromosome pairs with its homologous pair to form a Tetrad.

Tetrad: Structure containing 4 chromatids. Unique to meiosis. Homologous chromosomes pair up. Crossing-Over After homologous chromosomes pair up and form
a Tetrad, they exchange portions of their
chromatids in a process called Crossing-Over. Crossing-Over
Leads to genetic
variation! Meiosis 1 and Meiosis 2 Purposes Mitosis: Growth and Repair
-Two identical cells

Meiosis: Reproduction
-4 unique cells (sperm in males, eggs in females). Comparison of Mitosis and Meiosis Mitosis
1. Purpose: Growth/Repair
2. Division: 1
3. Parent Cell: Diploid
4. Daughter Cell: 2 Identical Diploid Cells
5. Somatic Cells Meiosis
1. Purpose: Reproduction
2. Division: 2
3. Parent Cell: Diploid
4. Daughter Cell: 4 Unique Haploid Cells
5. Reproductive Cells Meiosis Gametes are reproductive cells that unite during sexual reproduction. In humans, male gametes are sperm and female gametes are ova (eggs). Gametes=Haploid
Only one copy of
chromosomes Mitosis=Cell division for growth and repair.
Results in two identical cells.
Occurs in somatic cells


Meiosis=Cell division for reproduction.
Results in four genetically different cells.
Occurs in sex cells Compare and Contrast
What is one similarity and one difference between mitosis and meiosis?

Write on a half sheet of paper and bring to the front desk when completed. EXIT TICKET Meiosis 1 Meiosis 2 Crossing-over also happens in prophase 1.
Mitosis: Prophase, Metaphase, Anaphase, Telophase. Meiosis: Does each phase twice (2 divisions). Also, the chromosomes align differently in Metaphase. In males, gametes are made in the testes. In females, gametes are made in the ovaries. Meiosis Mitosis Mitosis vs Meiosis Mitosis-Somatic Cells Meiosis-Sex Cells


-2 Diploid Cells

- Both paternal and maternal chromosomes are present 4 Haploid Cells Does not have both paternal and maternal chromosomes Homologous Chromosomes
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