the number of chromosomes in the nucleus of an...
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Cytogenetics: Karyotypes and Chromosome Aberrations
Chapter 6
Chromosome Number
! The number of chromosomes in the nucleus of an organism is characteristic for a species
Fig. 6-2, p. 131
METACENTRIC SUBMETACENTRIC ACROCENTRIC
Stalk
Centromere Satellite
Long arm (q)
Short arm (p)
3 17 21
p
q
A Human Karyotype
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Karyogram: Chromosome Banding Patterns
Fig. 6-4a, p. 132
1 2 3 4 5 6
System of Naming Chromosome Bands
! Allows any region to be identified by a descriptive address (chromosome number, arm, region, and band)
Fig. 6-6, p. 133
Draw 10 to 20 ml of blood.
Add a few drops of blood.
Add phytohemagglutinin to stimulate mitosis.
Incubate at 37°C for 2 to 3 days.
Transfer to tube containing fixative.
Transfer cells to tube.
Add Colcemid to culture for 1 to 2
hours to stop mitosis in metaphase.
Centrifuge to concentrate cells.
Add low-salt solution to break open
red blood cells, swell lymphocytes.
Drop cells onto microscope slide.
Stain slide with Giemsa.
Examine with microscope.
Digitized chromosome
images processed to make karyotype.
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Metaphase Chromosomes Arranged Into a Karyotype Chromosomal Aberrations
Normal Karyotype Chromosome Painting with FISH
Chromosomal Abnormalities in a Cancer Cell
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Amniocentesis (week 15-20) Chorionic Villus Sampling (week 10-12)
A Triploid Karyotype A Triploid Infant
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Nondisjunction in Meiosis I Effects of Monosomy and Trisomy
! Autosomal monosomy is a lethal condition • Eliminated early in development (spontaneous
abortion)
! Autosomal trisomy is relatively common • Most result in spontaneous abortion • Three types can result in live births (13, 18, 21)
Trisomy 13: Patau Syndrome (47,+13)
! A lethal condition
Trisomy 18: Edwards Syndrome (47,+18)
! A lethal condition
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Trisomy 21: Down Syndrome (47,+21) Maternal Age and Trisomy 21
Turner Syndrome
! Monosomy of the X chromosome (45,X) that results in female sterility • One MZ twin with
Turner syndrome
Turner Syndrome (45,X)
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Klinefelter Syndrome
! Aneuploidy of the sex chromosomes involving an XXY chromosomal constitution
Klinefelter Syndrome (47,XXY)
XYY Syndrome (47,XYY) Structural Alterations Within Chromosomes
! Changes in the arrangement of chromosomes • Deletions • Translocations • Duplications • Inversions
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Structural Abnormalities In Chromosomes
Structural Abnormalities In Chromosomes
Structural Abnormalities In Chromosomes
Structural Abnormalities In Chromosomes
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Chromosomal Deletions Deletion: Cri du Chat
Robertsonian Translocation Chromosomal Abnormalities in Newborns
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Fig. 6-29, p. 152
Nondisjunction in one parent
followed by dup- lication in embryo
Nondisjunction in both parents Normal
Duplication
Embryo
Zygote
Gamete
Fragile Sites on the X Chromosome
Sites of chromosomal breakage
Fragile X syndrome
! f
Genetic Cause of Autism Trinucleotide repreats in FMR 1 gene on q arm of X chromosome