Meiosis Division of Sex Cells Meiosis A process

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Meiosis Division of Sex Cells

Meiosis Division of Sex Cells

Meiosis § A process of reduction division in which the number of chromosomes is

Meiosis § A process of reduction division in which the number of chromosomes is cut in half through separation of homologous pairs in a diploid cell. § Diploid – 2 sets of chromosomes § Haploid – 1 set of chromosomes § Homologous – pairs of matching chromosomes that come from each parent

Meiosis

Meiosis

Meiosis Stages § Meiosis involves 2 distinct cell divisions: § Meiosis II

Meiosis Stages § Meiosis involves 2 distinct cell divisions: § Meiosis II

Prophase I § Each chromosome pairs with its corresponding homologous chromosome to form a

Prophase I § Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. § There are 4 chromosomes in a tetrad. § The pairing of homologous chromosomes is the key to meiosis. § Crossing-over may occur here § Crossing-over is when chromosomes overlap and exchange portions of their DNA

Prophase I

Prophase I

Metaphase I § Spindle fibers attach to the chromosomes § Homologous pairs line up

Metaphase I § Spindle fibers attach to the chromosomes § Homologous pairs line up side by side

Metaphase I

Metaphase I

Anaphase I § The fibers pull the homologous chromosomes toward opposite sides.

Anaphase I § The fibers pull the homologous chromosomes toward opposite sides.

Anaphase I

Anaphase I

Telophase I & Cytokinesis § Nuclear membranes form. § The cell separates into 2

Telophase I & Cytokinesis § Nuclear membranes form. § The cell separates into 2 cells.

Telophase I

Telophase I

End of Meiosis I § Meiosis I results in two haploid (N) cells. §

End of Meiosis I § Meiosis I results in two haploid (N) cells. § Each cell has half the number of chromosomes as the original cell.

Prophase II § Chromosomes re-condense and nuclear membrane breaks down again (similar to Prophase

Prophase II § Chromosomes re-condense and nuclear membrane breaks down again (similar to Prophase of Mitosis)

Prophase II

Prophase II

Metaphase II § The chromosomes line up similar to metaphase in mitosis.

Metaphase II § The chromosomes line up similar to metaphase in mitosis.

Metaphase II

Metaphase II

Anaphase II § Sister chromatids separate and move to opposite sides.

Anaphase II § Sister chromatids separate and move to opposite sides.

Anaphase II

Anaphase II

Telophase II and Cytokinesis § Meiosis II results in 4 GENETICALLY DIFFERENT haploid cells.

Telophase II and Cytokinesis § Meiosis II results in 4 GENETICALLY DIFFERENT haploid cells. (gametes)

Telophase II

Telophase II

Gamete Formation § In males, meiosis results in 4 sperm cells (spermatogenesis)

Gamete Formation § In males, meiosis results in 4 sperm cells (spermatogenesis)

Gamete Formation § In females, meiosis results in 1 egg cell and three polar

Gamete Formation § In females, meiosis results in 1 egg cell and three polar bodies, which are not used in reproduction. (Oogenesis)

Mitosis vs Meiosis Results in Cells are Occurs in Mitosis 2 Diploid Cells (2

Mitosis vs Meiosis Results in Cells are Occurs in Mitosis 2 Diploid Cells (2 N) Genetically Identical Somatic (Body) Cells Meiosis 4 Haploid Cells (N) Genetically Different Sex Cells