a typical bio lab …… b // o o o
Post on 19-Dec-2015
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A typical bio lab ……
//www.youtube.com/watch?v=Vc1UqeHhjeo
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MeiosisUnlike mitosis, which occurs in somatic cells, meiosis has evolved to make sexual reproduction possible. Meiosis produces sex cells.
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Meiosis – the big picture
THIS PROCESS GENERATES
THE DIVERSITY OF ALL
SEXUALLY REPRODUCING
ORGANISMS. Including,
naturally, us.
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Asexual reproduction – no meiosis here
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Asexual reproduction – NOT meiosis
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Chromosome reduction …
How a father with 46 chromosomes in each cell and a mother with 46 chromosomes per cell can have a child with 46 chromosomes per cell.
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Diploid and Haploid Diploid cell – contains two of each
kind of chromosome, one from the male parent, one from the female parent ..... It is 2n. (2n = 46 in human)
Haploid cell – contains one of each kind of chromosome, from either of the parents ..... It is n. (n = 23 in human)
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Meiosis defined
Meiosis- process where the number of chromosomes per cell is cut in half through the separation of chromosomes in a diploid cell.
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Homologous chromosomes are …
A pair of chromosomes having
the same gene sequences, each derived from one parent.
So, the chromosomes have the same genes at the same loci but possibly different alleles.
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Gene – DNA sequence coding for protein. Basic unit of heredity.
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Allele – One member of a pair of genes occupying a specific spot on a chromosome (locus) that controls the same trait.
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Human Karyotype
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Haploid or Diploid?
Mitosis produces _________ cells.
Sex cells (eggs, sperm) are _________ cells.
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Phases (Stages) of Meiosis
Interphase I -- • cell replicates its DNA, like in mitosis • each chromosome now consists of 2 sister chromatids held together by a centromere
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Interphase
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Interphase
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Meiotic stages (cont’d.)
Prophase I -- • Chromosomes coil up • Spindle forms • Homologous chromosomes pair
up as tetrads • Crossing over occurs – genetic material exchanges between homologues
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Homologues in a tetrad … how romantic!
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Crossing over – very important
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Stirring the pot …
Crossing over - The chromosomes you receive from your mom’s egg and your dad’s sperm are NOT the same chromosomes that your mom and dad have. They are “shuffled” versions.
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How do we know this is .....
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Meiosis I stages (cont’d.)
Metaphase I – the centromere of each
chromosome becomes attached to a spindle fiber
the spindle fibers pull the tetrads to the equator of the spindle
homologous chromosomes are lined up side by side along the equator
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More shuffling …
Independent assortment – homologues line up or “shuffle” randomly on the metaphase plate in Meiosis I. 223 or 8 million possible assortments of chromosomes for every sperm cell. (Random fertilization – the ovum also has 8 million possible chromosome combos, so … 8 mill. X 8 mill. = 64 trillion possible diploid combinations in each zygote!!!)
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How do we know this is …..
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Metaphase I
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Metaphase I -- after crossing over
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Meiotic stages (cont’d.)
Anaphase 1: homologous chromosomes
separate and move to opposite ends of the
cell centromeres do not split this ensures that each new cell will
receive only one chromosome from each homologous pair
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How do we know this is …..
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Meiotic stages (cont’d.)
Telophase 1: the spindle breaks down and the
chromosomes uncoil the cytoplasm divides to yield two
new cells each cell has half the genetic
information of the original cell because it has only one homologous
chromosome from each pair
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How do we know this is …..
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Cell plate forms …..
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Meiosis II – mitosis of the products of Meiosis I
Prophase II- a spindle forms in each of the two
new cells and the fibers attach to the chromosomes
Metaphase II- the chromosomes are pulled to the
center of the cell and line up randomly at the equator
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How do we know this is …..
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How do we know this is …..
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Meiosis II – mitosis of the products of Meiosis I (cont’d.)
Anaphase II- the centromere of each
chromosome splits the sister chromatids separate and
move to opposite poles Telophase II- -nuclei re-form -the spindles break down -the cytoplasm divides
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How do we know this is …..
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The spindle
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How do we know this is …..
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What Meiosis produces:
four haploid sex cells from one original diploid cell
-each haploid cell contains one chromosome from each homologous pair
-haploid cells will become gametes transmitting genes to offspring
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A different type of tetrad ….
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Put it together …
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Don’t blink …
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Meiosis overview
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Spermatogenesis
Spermatogenesis -- in testes. 2 months from start to finish. Every day, several hundred million sperm are made by meiosis! Spermatogonia – 2n, undergo meiosis Primary spermatocytes – 2n, meiosis I. 23 pairs of homologues incl. X,Y Spermatids – n, meiosis II, 23 chromosomes, incl. X or Y Spermatozoa - n, pumped and ready to roll
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Oogenesis Oogenesis – in ovaries. 15 – 30
years from start to finish. Developmental arrest in Meiosis I until a girl goes through puberty.
Oogonia - 2n. 2 million are formed in a baby girl before birth!
Oocytes – primary, meiosis I … 2n. 23 pairs of homologues including XX chromosomes. A few progress through meiosis every 28 days. secondary, meiosis II … 23 chromosomes including an X chromosome. All made up and lookin’ to party.
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And finally ……
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Meiosis videos
http://www.youtube.com/watch?v=uh7c8YbYGqo
http://www.youtube.com/watch?v=D1_-mQS_FZ0
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http://bio.rutgers.edu/~gb101/lab10_meiosis/meiosis_web/index10.html
Meiosis phase I.D. lab
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Mitosis vs Meiosis
http://www.pbs.org/wgbh/nova/baby/divide.html#
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Meiosis Animation Links
Animation How Meiosis Works.mht
Meiosis animation 2.mht
Animation Stages of Meiosis 3.mht
YouTube - Meiosis.mht
Meiosis An Interactive Animation Cells Alive.mht
YouTube - Meiosis.mht
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Meiosis Quiz
http://www.biologycorner.com/bio1/qz_meiosis.html