Meiosis: Formation of gametes Utilizing BioCoach Activity “Meiosis”
MEIOSIS Chapter 10.2. Meiosis This kind of cell division produces gametes containing half the...
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Transcript of MEIOSIS Chapter 10.2. Meiosis This kind of cell division produces gametes containing half the...
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MEIOSISMEIOSISChapter 10.2
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MeiosisMeiosis This kind of cell division
produces gametes containing half the number of chromosomes as a parent’s body cell
Meiosis consists of 2 separate divisions known as Meiosis I and Meiosis II
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Diploid cellsDiploid cells Diploid means 2 sets Cell that contains both sets of
homologous chromosomes (one set from each parent)
2n
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Haploid cellsHaploid cells Gametes or reproductive
cells Haploid means one set Contain only a single set of
chromosomes n
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Homologous chromosomesHomologous chromosomes Paired chromosomes 2 chromosomes of each pair in a
diploid cell Each of a pair of homologous
chromosomes has genes for the same traits
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Meiosis IMeiosis I Begins with one diploid (2n) cell During meiosis, a spindle forms and
the cytoplasm divides in the same ways they do during mitosis.
However, what happens to the chromosomes in meiosis is very different
Phases: Prophase I, Metaphase I, Anaphase I, & Telophase I
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Prophase IProphase I Chromosomes coil up and spindle
forms Each pair of homologous
chromosomes comes together, matched gene by gene to form a 4 part structure called a tetrad.
Tetrad consists of 2 homologous chromosomes, each made up of 2 sister chromatids
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Crossing overCrossing over Tetrads are paired so tightly that
non-sister chromatids from homologous chromosomes sometimes actually exchange genetic material in a process known as crossing over.
Crossing over results in new combinations of genes on a chromosome.
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Metaphase IMetaphase I Centromere of each
chromosome becomes attached to a spindle fiber
The spindle fibers pull the tetrads into the middle of the spindle
Homologous chromosomes are lined up side by side as tetrads
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Anaphase IAnaphase I Homologous chromosomes,
each with its 2 chromatids, separate and move to opposite ends of the cell.
Centromeres holding sister chromatids together do not split
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Telophase ITelophase I Spindle is broken down, the
chromosomes uncoil and cytoplasm divides to yield 2 new cells.
Each cell has only half the genetic information of the original cell
Another cell division is needed because each chromosome is still doubled, consisting of 2 sister chromatids
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http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter11/meiosis_i.html
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Meiosis IIMeiosis II Ends with 4 haploid (n) cells These haploid cells are called sex cells
or gametes Male = sperm Female = egg When a sperm fertilizes an egg, a zygote results
with a diploid number of chromosomes. Zygote can then develop by mitosis into a
multicellular organism. Phases: Prophase II, Metaphase II, Anaphase II,
Telophase II
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Newly formed cells in some organisms undergo a short interphase in which the chromosomes do not replicate
In other organisms, however, the cells go from late anaphase of meiosis I directly to metaphase of meiosis II, skipping telophase I, interphase & prophase II.
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Prophase IIProphase II A spindle forms in each of
the 2 new cells and the spindle fibers attach to the chromosomes
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Prophase II
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Metaphase IIMetaphase II The chromosomes, still made
up of sister chromatids, are pulled to the center of the cell and line up randomly at the equator.
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Metaphase II
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Anaphase IIAnaphase II Centromere of each
chromosome splits, allowing the sister chromatids to separate and move to opposite poles
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Anaphase II
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Telophase IITelophase II Nuclei reform Spindle breaks down Cytoplasm divides Each haploid cell contains one
chromosome from each homologous pair
These haploid cells will become gametes, transmitting the genes they contain to offspring
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Telophase IIhttp://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter11/meiosis_ii.html
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Cells that are formed by mitosis are identical to each other and to the parent cell
Meiosis however, provides a mechanism for shuffling the chromosomes and the genetic info they carry.
By shuffling the chromosomes, genetic variation is produced