Boo-Yah Biology! Meiosis Molecular Biology Sumner HS

Quick Mitosis Review Mitosis important in growth & repair Produces genetically identical daughter cells. DNA replicated in S phase Copies divided into daughter cells during mitosis (PMAT) & cytokinesis. Daughter cells have the diploid number of chromosomes. (humans = 46, or 23 pair)

Meiosis Making Reproductive Cells (Sexual Reproduction)

Meiosis Fundamentals Meiosis is a process of cell division that reduces the number of chromosome sets from diploid to haploid, producing 4 cells. Takes place in two sets of divisions, meiosis I and meiosis II It is this process that organisms use to make sperm and egg cells

Meiosis Fundamentals Chromosomes replicate once. Two consecutive nuclear divisions (similar stages to mitosis) Meiosis 1 Meiosis 2 Results in four haploid cells. Reduces Chromosome number in half.

Meiosis Fundamentals Why do we want reproductive cells to be haploid?

Two stages of Meiosis Meiosis I Reduces the number of chromosomes from 4n to 2n, producing 2 cells. Homologous chromosomes separate Meiosis II Sister chromatids separate Produces four haploid (n) daughter cells

Chromosome Accounting

9 Regular human body cell = 46 total chromosomes The total number of chromosomes in a regular cell is the diploid number (46 in humans). Or 2n = 46 Or 23 pairs The number of chromosomes received from each parent is the haploid number (23 in humans) Or n = 23 Or 23 total

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12 Chromosomes and the Cell Cycle During G1 = 2n = 46 During S & G2 = 4n = 92 (DNA is replicated) After Cytokinesis = 2n = 46 Mitosis produces genetically identical cells.

Organism Life Cycles At sexual maturity, the ovaries and testes produce haploid gametes by meiosis. n = 23 Not genetically identical to parent cell due to only having half of the total chromosome set During fertilization these gametes (sperm and ovum) fuse, forming a diploid zygote The zygote develops into an adult organism

Life cycle

Homologous chromosomes What is a homologous chromosome? The pair of chromosomes from each parent Ex: Homologous chromosome 1: 1 from Mom and 1 from Dad

Homologous Chromosome What is a homologous chromosome? The pair of chromosomes from each parent Ex: Homologous chromosome 1: 1 from Mom and 1 from Dad

The human genome: _Genome/posters/chromosome/chooser.shtml _Genome/posters/chromosome/chooser.shtml Meiosis: A A

Meiosis: The Steps

The Steps of Meiosis I Interphase Chromosomes duplicate (4n) Prophase I Homologous replicated chromosomes pair forming tetrads (four chromatids) and exchange gene segments = crossing over

Steps of Meiosis I Metaphase 1 Tetrads line up on cell equator Spindles attached to centromere

Steps of Meiosis I Anaphase I Homologous chromosome pairs separate Sister chromatids still attached

Steps of Meiosis I Telophase I/Cytokinesis New nuclei form Cytokinesis produces two non-identical diploid cells Chromosomes still as sister chromatids.

Steps of Meiosis II Prophase II Much like prophase in mitosis Preparation for division

Steps of Meiosis II Metaphase II Homologous pairs line up on the metaphase plate (equator) Spindle attaches to centromere

Steps of Meiosis II Anaphase II Sister chromatids separate Pulled to opposite ends of the cell.

Steps of Meiosis II Telophase II/ Cytokinesis New nuclei forming New cells are haploid, not diploid Cells divide Four non-identical daughter cells formed.

Meiosis Accounting During G1 = 2n = 46 During S & G2 = 4n = 92 (DNA is replicated) After Cytokinesis I = 2n = 46 After Cytokinesis II = n = 23

Meiosis animation

Now we dance! Two groups: mitosis vs. meiosis Resources: steps of mitosis & meiosis Major roles: chromosomes, membranes Prepare to create a “dance” showing how your style of cell division works.

The Big Picture

Comparison

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