4.2.4 Explain that non-disjunction can lead to changes in chromosome number

00:02:19
https://www.youtube.com/watch?v=CgGm_hUFiY0

概要

TLDRThis video elaborates on the concept of nondisjunction in meiosis, emphasizing its occurrence during anaphase 1 and anaphase 2. In meiosis 1, homologous chromosomes may fail to separate, resulting in daughter cells with either an extra or a missing chromosome. In meiosis 2, sister chromatids may similarly fail to separate. If this nondisjunction happens with chromosome 21, it can lead to gametes with an abnormal number of these chromosomes. Fertilization of such gametes may produce a zygote with three copies of chromosome 21, leading to Down syndrome, which can be confirmed through karyotype analysis to detect the presence of trisomy 21.

収穫

  • 🧬 Nondisjunction is the failure to separate chromosomes during meiosis.
  • 📉 Occurs in anaphase 1 or anaphase 2 of meiosis.
  • 🔄 Anaphase 1 results in one daughter cell with an extra chromosome (n+1) and another with one less (n-1).
  • 🔄 Anaphase 2 results in one extra chromosome, one less, and two normal cells.
  • 👶 Nondisjunction of chromosome 21 can cause Down syndrome.
  • 🧬 Down syndrome results from three copies of chromosome 21 (trisomy 21).
  • 🧪 Identified through karyotype analysis.

タイムライン

  • 00:00:00 - 00:02:19

    Nondisjunction is the failure of chromosomes to separate during meiosis, specifically during anaphase I of meiosis I and anaphase II of meiosis II. In anaphase I, homologous chromosomes fail to separate, leading to daughter cells with either an extra chromosome (n + 1) or one less (n - 1). In anaphase II, sister chromatids do not separate, resulting in one cell with n + 1, one with n - 1, and two with the normal number of chromosomes. If nondisjunction affects chromosome 21, it can produce gametes with extra copies, potentially resulting in Down syndrome when fertilization occurs with a normal gamete. This condition can be identified by a karyotype showing three copies of chromosome 21 (trisomy 21) and indicates the individual's sex.

マインドマップ

ビデオQ&A

  • What is nondisjunction?

    Nondisjunction refers to the failure to separate homologous pairs of chromosomes or sister chromatids during meiosis.

  • Where does nondisjunction occur in meiosis?

    Nondisjunction can occur during anaphase 1 of meiosis 1 or anaphase 2 of meiosis 2.

  • What can result from nondisjunction in meiosis?

    Nondisjunction can lead to gametes with extra or missing chromosomes, potentially resulting in genetic disorders.

  • What does Down syndrome result from?

    Down syndrome results from having three copies of chromosome 21, known as trisomy 21.

  • How can Down syndrome be identified?

    Down syndrome can be identified by examining karyotypes for three copies of chromosome 21.

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  • 00:00:04
    nondisjunction refers to the failure to
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    separate as this applies to meiosis it
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    is the failure of homologous pairs to
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    separate during anaphase 1 of meiosis 1
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    or of cyto chromatids to separate during
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    anaphase 2 of meiosis
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    2 this first example shows
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    non-disjunction in anaphase 1 of meiosis
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    1 and so you see the pink homologous
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    pair of chromosomes fail to separate
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    this therefore results in half of the
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    daugh cells containing one extra
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    chromosome or n +1 and the other half of
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    the D cells containing one less
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    chromosome or n minus
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    one in this second example we'll show
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    non-disjunction in anaphase 2 of meiosis
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    2 so you can see the pink sister
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    chromatids on the left hand side fail to
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    separate into separate daughter cells
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    of the four daughter cells produced in
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    this example one of them will have one
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    extra chromosome n +1 one will be short
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    by one chromosome n minus one and the
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    other two will have the normal number of
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    chromosomes
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    n now if this nondisjunction were to
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    occur in either meiosis 1 or meiosis 2
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    to chromosome number 21 this would
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    result in one of the gamuts having two
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    copies of chromosome number 2
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    during fertilization if one of these
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    gamuts with n +1 or two copies of
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    chromosome number 21 fuses with one with
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    a normal number of chromosomes one copy
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    of chromosome number 21 then the result
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    is a cell with 2 N +1 chromosomes or
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    three copies of chromosome number 21 and
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    this results in Down
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    syndrome Down syndrome can be identified
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    on a car type by looking for three
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    copies of chromosome number 21 known as
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    tric 21 the carot type will also show
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    whether the individual is a male XY or a
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    female XX
タグ
  • nondisjunction
  • meiosis
  • anaphase
  • chromosomes
  • Down syndrome
  • trisomy 21
  • gametes
  • fertilization
  • karyotype