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Chromosomal Abnormalities Errors of Meiosis. Chromosomal abnormalities. Incorrect number of chromosomes nondisjunction chromosomes don’t separate properly during meiosis chromosome structure mutations deletion duplication inversion translocation. n. n. Nondisjunction.

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Presentation Transcript
slide1

Chromosomal Abnormalities

Errors of Meiosis

chromosomal abnormalities
Chromosomal abnormalities
  • Incorrect number of chromosomes
    • nondisjunction
      • chromosomes don’t separate properly during meiosis
    • chromosome structure mutations
      • deletion
      • duplication
      • inversion
      • translocation
nondisjunction

n

n

Nondisjunction
  • Problems in meiosis cause errors in daughter cells
    • chromosome pairs do not separate properly during Meiosis 1
    • sister chromatids fail to separate during Meiosis 2
    • too many or too few chromosomes

2n

n-1

n+1

nondisjunction1
Nondisjunction
  • Baby has wrong chromosome number
    • trisomy
      • cells have 3 copies of a chromosome
    • monosomy
      • cells have only 1 copy of a chromosome

n-1

n

n+1

n

monosomy

2n-1

trisomy

2n+1

human chromosome disorders
Human chromosome disorders
  • High frequency in humans
    • most embryos are lost to miscarriage
    • alterations are too disastrous
    • developmental problems result from biochemical problems
  • Certain conditions are tolerated
    • upset the balance less = survivable
    • characteristic set of symptoms = syndrome
down syndrome
Down syndrome
  • Trisomy 21
    • 3 copies of chromosome 21
    • 1 in 700 children born in U.S.
  • Chromosome 21 is the smallest human chromosome
    • but still severe effects
  • Frequency of Down syndrome is related tothe age of the mother
slide9

Chapter 12

Detecting Genetic Disease

  • Genetic screening examines a person’s genetic makeup and potential risks of passing disorders to offspring.
  • Amniocentesis and chorionic villi sampling help physicians test a fetus for the presence of genetic disorders.
slide10
Amniocentesis – 14-16 weeks
    • sample of embryo cells
    • stain & photograph chromosomes
  • Chorionic villi sampling – 8-10 weeks
    • Cells derived from the embryo that grow between the mother’s uterus and the placenta
  • Analysis of karyotype
sex chromosomes abnormalities
Sex chromosomes abnormalities
  • Human development more tolerant of wrong numbers in sex chromosome
  • But produces a variety of distinct syndromes in humans
    • XXY = Klinefelter’s syndrome male
    • XXX = Trisomy X female
    • XYY = Jacob’s syndrome male
    • XO = Turner syndrome female
klinefelter s syndrome
Klinefelter’s syndrome
  • XXY male
    • one in every 2000 live births
    • have male sex organs, but are sterile
    • feminine characteristics
      • some breast development
      • lack of facial hair
    • tall
    • normal intelligence
jacob s syndrome male
Jacob’s syndrome male
  • XYY Males
    • 1 in 1000 live male births
    • extra Y chromosome
    • slightly taller than average
    • more active
    • normal intelligence, slight learning disabilities
    • delayed emotional immaturity
    • normal sexual development
turner syndrome
Turner syndrome
  • Monosomy X or X0
    • 1 in every 5000 births
    • varied degree of effects
    • webbed neck
    • short stature
    • sterile
changes in chromosome structure
Changes in chromosome structure
  • deletion
    • loss of a chromosomal segment
  • duplication
    • repeat a segment
  • inversion
    • reverses a segment
  • translocation
    • move segment from one chromosome to another
slide16
Translocation disorders: Partial errors in chromosomes can occur, where a person still only has a pair, but accidentally has entire sequences misplaced.
  • Translocations are the transfer of a piece of one chromosome to a nonhomologous chromosome. Translocations are often reciprocal; that is, the two nonhomologues swap segments.