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

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.

Metaphase Chromosomes Arranged Into a Karyotype Chromosomal Aberrations

Normal Karyotype Chromosome Painting with FISH

Chromosomal Abnormalities in a Cancer Cell

Amniocentesis (week 15-20) Chorionic Villus Sampling (week 10-12)

A Triploid Karyotype A Triploid Infant

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

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)

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

Structural Abnormalities In Chromosomes

Structural Abnormalities In Chromosomes

Structural Abnormalities In Chromosomes

Structural Abnormalities In Chromosomes

Chromosomal Deletions Deletion: Cri du Chat

Robertsonian Translocation Chromosomal Abnormalities in Newborns

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