Chromosomes
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Transcript of Chromosomes
![Page 1: Chromosomes](https://reader036.fdocuments.net/reader036/viewer/2022062321/568134df550346895d9c113c/html5/thumbnails/1.jpg)
Chromosomes
• Each organism has a set # of chromosomes
• Individuals of the same species have the same # of chromosomes
• Humans– 46
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Karyotype
• Display of chromosomes
• All the chromosomes in a cell
• Arranged by homologous chromosomes
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Homologous Chromosomes
• One from each parent• There are 23 pairs of
homologous chromosomes in each body cell
• Have the same sequence of genes on DNA
• Control the same traits
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More Karyotypes
• Normal Male– 22 pairs of body
chromosomes
– 1 pair of sex chromosomes• 1 X Chromosome
• 1Y Chromosome
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• Normal Female– 22 pairs of body
chromosomes
– 1 pair of sex chromosomes
• 2 X chromosomes
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Diploid
• Contain 2 of ever chromosome
• 46 is the diploid # in humans
• 2n• Body Cells
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Haploid
• Contain 1 of each chromosome
• 23 is the haploid # in humans
• n• Sex Cells
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What does this have to do with anything?
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SEX!
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Fertilization
• The fusion between the sperm and the egg
• Creates a Zygote– The first cell of a
human
• 23 chromosomes from the male and 23 chromosomes from the female (46 total)
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How do we make sex cells?
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Meiosis (sex cell division)
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Let’s Remember…
• In Mitosis– Each of the 46 chromosomes double in
interphase…92 total chromosomes at the start of prophase
– The doubled chromosome
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Interphase I:
• Each chromosome has been replicated, exactly as in mitosis.
• The cell grows in size.
Lily Anther Cell: Meiosis I (Male)
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Prophase I:
• The chromosomes shorten and thicken.
• The nuclear membrane disappears.
• Homologous chromosomes stick to each other and form a Tetrad.
• Crossing Over occurs
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Metaphase I:
• The spindle fibers form.
• The centromeres (middle of the tetrad) become attached to the spindle fibers.
• The chromosomes line up in the middle of the cell.
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Anaphase I:
• Double-stranded homologous chromosomes move apart.
• The homologous chromosomes that separated are different.
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Telophase I:
• The chromosomes are at opposite poles.
• Cytokinesis separates the two new nuclei into two haploid sister cells.
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Prophase II:
• The chromatids of each chromosome are not wound tightly around each other.
• Spindle fibers form again.
Lily Anther Cell: Meiosis II
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Metaphase II:
• The chromosomes line up in the middle.
• Note that both sister cells are undergoing the process at the same time.
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Anaphase II:
• The sister centromeres and the sister chromatids separate.
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Telophase II:
• The chromatids are at opposite poles.
• Cytokinesis splits the cells
• The result is four separate haploid cells.
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Mitosis makes Body Cells
• 1 cell division• Produces 2 cells• The same number of chromosomes as the parent
cell• 46 Chromosomes in humans• Creates body cells (somatic)
– Blood, bone, muscle, nerve, skin…
• Takes place all over your body except in your testes or ovaries.
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Meiosis makes sex cells
• 2 cell divisions• Produces four cells• 1/2 the number of chromosomes as the parent• 23 chromosomes in humans• Creates sex cells (gametes)
– Sperm
– Egg
• Takes place in the testes and ovaries
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Errors in Meiosis (Nondisjunction)
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Ex. Down Syndrome
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Errors in Meiosis(Translocation)
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Ex. •Leukemia•Carcinomas
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Errors in Meiosis(Deletion)
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Ex. •Muscular Dystrophy•Cri-Du-Chat Syndrome