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Meiosis Gamete Production

Meiosis Gamete Production. Timothy G. Standish, Ph. D. A packaged chromosome. Chromatid. Identical chromatid. Replication. Anaphase. Chromosomes, Chromatids and Centromeres. Chromosome arm. Two identical chromosomes. Centromere. Chromosome arm. In The Beginning Two.

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Meiosis Gamete Production

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  1. MeiosisGamete Production Timothy G. Standish, Ph. D.

  2. A packaged chromosome Chromatid Identical chromatid Replication Anaphase Chromosomes, Chromatids and Centromeres Chromosome arm Two identical chromosomes Centromere Chromosome arm

  3. In The Beginning Two • Humans and many other complex multicelled organisms incorporate genetic recombination in their reproduction • Reproduction in which there is a re-mixing of the genetic material is called sexual reproduction • Two cells, a sperm and an egg, unite to form a zygote, the single cell from which the organism develops • Meiosis is the process of producing sperm and eggs (gametes)

  4. Egg 1n Haploid nucleus Sperm 2n Haploid nucleus Fertilization Results In A Diploid Zygote

  5. Fertilization Results In A Diploid Zygote Egg 1n Haploid nucleus Sperm 2n Haploid nucleus

  6. Haploid nucleus Fertilization Results In A Diploid Zygote Egg 1n Haploid nucleus Sperm 2n

  7. Haploid nucleus Fertilization Results In A Diploid Zygote Egg 1n Haploid nucleus Sperm 2n

  8. Zygote 2n Zygote 2n From Zygote to Embryo

  9. From Zygote to Embryo Cleavage

  10. From Zygote to Embryo Cleavage

  11. From Zygote to Embryo Cleavage

  12. From Zygote to Embryo Cleavage

  13. From Zygote to Embryo Morula

  14. Gametes Are Haploid • Gametes must have half the genetic material of a normal cell • If the genetic material in the gametes was not halved, when they combined the zygote would have more genetic material than the parents • Meiosis is specialized cell division resulting in cells with half the genetic material of the parents • Gametes have exactly one set of chromosomes, this state is called haploid (1n) • Regular cells have two sets of chromosomes, this state is called diploid (2n)

  15. Stages Of Meiosis • Meiosis resembles mitosis except that it is actually two divisions, not one • These divisions are called Meiosis I and Meiosis II • Meiosis I results in haploid cells with chromosomes made up of two chromotids • Meiosis II is essentially mitosis on haploid cells • Stages of meiosis resemble mitosis with two critical differences: the first in Prophase I and the second in Metaphase I

  16. Stages Of Meiosis - Meiosis I • Prophase I - The beginning phase - • DNA which was unraveled and spread all over the nucleus is condensed and packaged • Homologous chromosomes (each made of two identical chromatids) come together and form tetrads (4 chromatids) • Crossing over, in which chromatids within tetrads exchange genetic material, occurs • Metaphase I - Middle stage - Tetrads line up along the equator of the cell

  17. Stages Of Meiosis - Meiosis I • Anaphase I - One copy of each chromosome still composed of two chromatids moves to each pole of the cell • Telophase I - End stage - New nuclear membranes are formed around the chromosomes and cytokinesis (cytoplasm division) occurs resulting in two haploid daughter cells

  18. Stages Of Meiosis - Meiosis II • Prophase II - Cells do not typically go into interphase between Meiosis I and II, thus chromosomes are already condensed • Metaphase II - Chromosomes line up at the equator of the two haploid cells produced in meiosis I • Anaphase II - Chromosomes made up of two chromatids split to make chromosomes with one chromatid which migrate to the poles of the cells • Telophase II - Cytokinesis and reformation of the nuclear membrane in haploid cells each with one set of chromosomes made of one chromatid

  19. Mother cell Interphase Prophase I: Condensing Chromosomes Prophase I: Tetrad formation/ crossing over Metaphase I Meiosis II Anaphase I Telophase I Stages Of Meiosis: Meiosis I

  20. Metaphase II Anaphase II Telophase II Stages Of Meiosis: Meiosis II The products of meiosis are 4 haploid cells each with a unique set of chromosomes. Telophase I Prophase II The products of mitosis are 2 diploid cells with identical chromosomes.

  21. Prophase I: Tetrad formation/ crossing over Metaphase I Telophase I Telophase II Anaphase I Crossing Over Because of crossing over, every gamete receives a unique set of genetic information.

  22. The End

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