1. Meiosis
Chapter 11
Section 4

2. MT: Sexual Reproduction
Understand that homologous chromosomes separate randomly during meiosis to produce haploid gametes.
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3. What is happening here?
Fertilization!
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4. = when a male and female gamete join
fertilization
= when a male and female gamete join
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5. Chromosome #
Most organisms are diploid and thus want an offspring that is also diploid
So, each gamete has to be haploid so when they join they create a diploid organism
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6. ½ + ½ = 1 haploid + haploid = diploidOR
Female gamete male gamete = offspring
½ + ½ = 1
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7. Find chromosome # Human __ chromosomes Human 46 chromosomes
HAPLOID #
Human __ chromosomes
Dog __ chromosomes
Carrot __ chromosomes
Goldfish __ chromosomes
Wheat __ chromosomes
Tobacco __ chromosomes
DIPLOID #
Human 46 chromosomes
Dog 78 chromosomes
Carrot 18 chromosomes
Goldfish 94 chromosomes
Wheat 42 chromosomes
Tobacco 48 chromosomes
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8. What happens during the process of meiosis?
making of non-identical haploid gametes
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9. Telophase I and Cytokinesis
Phases of Meiosis I
Meiosis I
Meiosis I
Interphase I
During meiosis, the number of chromosomes per cell is cut in half through the separation of the homologous chromosomes. The result of meiosis is 4 haploid cells that are genetically different from one another and from the original cell.
Prophase I
Metaphase I
Anaphase I
Telophase I and Cytokinesis
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10. Interphase 1 DNA copies itself centrioles nucleus
Interphase I - Cells undergo a round of DNA replication, forming duplicate chromosomes.
nucleus
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11. Prophase I Homologous chromosomes pair up to form a tetrad.
Nuclear membrane disappears.
Homologous chromosomes pair up to form a tetrad.
Tetrad = 4 sister chromatids
Crossing over occurs
MEIOSIS I Prophase I - Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
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12. Does crossing over always occur at the same allele?
When homologous chromosomes form tetrads in meiosis I, they exchange portions of their chromatids in a process called crossing over.
Crossing-over produces new combinations of alleles.
Crossing-over occurs during meiosis. (1) Homologous chromosomes form a tetrad. (2) Chromatids cross over one another. (3) The crossed sections of the chromatids are exchanged.
Does crossing over always occur at the same allele?
NO! It is random
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13. Homologous chromosomes line up in middle of cell
Metaphase 1
Homologous chromosomes line up in middle of cell
Spindle fibers attach to the chromosomes.
MEIOSIS I Metaphase I - Spindle fibers attach to the chromosomes.
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14. Anaphase 1
The fibers pull the homologous chromosomes toward opposite ends of the cell.
MEIOSIS I Anaphase I - The fibers pull the homologous chromosomes toward opposite ends of the cell.
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15. The cell separates into two cells.
Telophase 1
Nuclear membranes form.
The cell separates into two cells.
MEIOSIS I Telophase I and Cytokinesis - Nuclear membranes form. The cell separates into two cells.
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16. Telophase II and Cytokinesis
Phases of Meiosis II
Meiosis II
During meiosis, the number of chromosomes per cell is cut in half through the separation of the homologous chromosomes. The result of meiosis is 4 haploid cells that are genetically different from one another and from the original cell.
Meiosis II
Telophase I and Cytokinesis I
Metaphase II
Anaphase II
Telophase II and Cytokinesis
Prophase II
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17. Nuclear membrane disappears.
Prophase ii
Nuclear membrane disappears.
MEIOSIS II Prophase II - Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original cell.
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18. Individual chromosomes line up in the middle of cell.
Metaphase ii
Individual chromosomes line up in the middle of cell.
MEIOSIS II Metaphase II - The chromosomes line up in a similar way to the metaphase state of mitosis.
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19. Anaphase ii
The sister chromatids separate and move toward opposite ends of the cell.
MEIOSIS II Anaphase II - The sister chromatids separate and move toward opposite ends of the cell.
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20. Meiosis II results in four non-identical haploid cells.
Telophase ii
Meiosis II results in four non-identical haploid cells.
MEIOSIS II Telophase II and Cytokinesis - Meiosis II results in four haploid (N) daughter cells.
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21. Gamete Formation
In male animals, meiosis results in four equal- sized gametes called sperm.
Meiosis produces four genetically different haploid cells. In males, meiosis results in four equal-sized gametes called sperm.
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22. Gamete Formation
In many female animals, only one egg results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction.
Meiosis produces four genetically different haploid cells. In females, only one large egg cell results from meiosis. The other three cells, called polar bodies, usually are not involved in reproduction.
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23. Websites to check out 1. http://www.cellsalive.com/meiosis.htm1. 2. 4.
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