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Meiosis Gamete Production

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Title: Foundations of Biology Subject: Chromosomal Basis of Inheritance Author: T. G. Standish Last modified by: wmc user Created Date: 8/30/1956 11:14:58 AM – PowerPoint PPT presentation

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Title: Meiosis Gamete Production


1
MeiosisGamete Production
2
Chromosomes, Chromatids and Centromeres
Chromosome arm
Two identical chromosomes
Centromere
Chromosome arm
3
In The Beginning Two
  • Humans and many other complex multi-celled
    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
Fertilization Results In A Diploid Zygote
5
Fertilization Results In A Diploid Zygote
Egg 1n
Haploid nucleus
Sperm 2n
Haploid nucleus
6
Fertilization Results In A Diploid Zygote
Egg 1n
Haploid nucleus
Sperm 2n
7
Fertilization Results In A Diploid Zygote
Egg 1n
Haploid nucleus
Sperm 2n
8
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
Stages Of Meiosis Meiosis I
20
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
Crossing Over
Because of crossing over, every gamete receives a
unique set of genetic information.
22
  • www.pbs.org/wgbh/nova/miracle/divide.html
    meiosis animation from NOVA
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