©2000 Timothy G. Standish Meiosis Gamete Production Timothy G. Standish, Ph. D.
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Transcript of ©2000 Timothy G. Standish Meiosis Gamete Production Timothy G. Standish, Ph. D.
©2000 Timothy G. Standish
MeiosisMeiosisGamete ProductionGamete Production
Timothy G. Standish, Ph. D.
©2000 Timothy G. Standish
Replication
Chromosomes, Chromatids Chromosomes, Chromatids and Centromeresand Centromeres
Centromere
Chromosome arm
Chromosome arm
Identicalchromatid
Chromatid
Anaphase
A packaged chromosome
Two identical chromosomes
©2000 Timothy G. Standish
In The Beginning TwoIn 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)
©2000 Timothy G. Standish
Egg1n
Haploidnucleus
Fertilization Results In A Fertilization Results In A Diploid ZygoteDiploid Zygote
Sperm2nHaploid
nucleus
©2000 Timothy G. Standish
Sperm2n
Fertilization Results In A Fertilization Results In A Diploid ZygoteDiploid Zygote
Egg1n
Haploidnucleus
Haploidnucleus
©2000 Timothy G. Standish
Sperm2n
Fertilization Results In A Fertilization Results In A Diploid ZygoteDiploid Zygote
Egg1n
Haploidnucleus
Haploidnucleus
©2000 Timothy G. Standish
Sperm2n
Fertilization Results In A Fertilization Results In A Diploid ZygoteDiploid Zygote
Egg1n
Haploidnucleus
Haploidnucleus
©2000 Timothy G. Standish
From Zygote to EmbryoFrom Zygote to Embryo
Zygote2n
Zygote
2n
©2000 Timothy G. Standish
Cleavage
From Zygote to EmbryoFrom Zygote to Embryo
©2000 Timothy G. Standish
Cleavage
From Zygote to EmbryoFrom Zygote to Embryo
©2000 Timothy G. Standish
Cleavage
From Zygote to EmbryoFrom Zygote to Embryo
©2000 Timothy G. Standish
Cleavage
From Zygote to EmbryoFrom Zygote to Embryo
©2000 Timothy G. Standish
Morula
From Zygote to EmbryoFrom Zygote to Embryo
©2000 Timothy G. Standish
Gametes Are HaploidGametes 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)
©2000 Timothy G. Standish
Stages Of MeiosisStages 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
©2000 Timothy G. Standish
Stages Of Meiosis - Meiosis IStages 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
©2000 Timothy G. Standish
Stages Of Meiosis - Meiosis IStages 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
©2000 Timothy G. Standish
Stages Of Meiosis - Meiosis IIStages 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
©2000 Timothy G. Standish
InterphaseInterphase
Mother cell Stages Of Meiosis: Stages Of Meiosis: Meiosis IMeiosis I
Meiosis IIMeiosis II
Prophase I:Tetrad formation/
crossing over
Prophase I:Tetrad formation/
crossing overMetaphase I Metaphase I
Telophase ITelophase I
Prophase I:Condensing
Chromosomes
Prophase I:Condensing
Chromosomes
Anaphase I Anaphase I
Telophase ITelophase I
Stages Of Meiosis: Stages Of Meiosis: Meiosis IIMeiosis II
Metaphase II Metaphase II
Anaphase II Anaphase II
Telophase II Telophase II
The products of mitosis are 2 diploid cells with identical chromosomes.
The products of meiosis are 4 haploid cells each with a unique set of chromosomes.Prophase IIProphase II
©2000 Timothy G. Standish
Prophase I:Tetrad formation/
crossing over
Prophase I:Tetrad formation/
crossing over
Crossing OverCrossing Over
Anaphase I Anaphase I
Telophase II Telophase II
Metaphase I Metaphase I
Telophase ITelophase IBecause of crossing over, every gamete receives a unique set of genetic information.
©2000 Timothy G. Standish