chapter 8 chromosomal structure and chromosomal mutations
TRANSCRIPT
Chapter 8Chapter 8
Chromosomal Structure and Chromosomal Mutations
ObjectivesObjectives
Define mutations and polymorphisms. Distinguish the three types of DNA mutations:
genome, chromosomal, and gene. Diagram a human chromosome and label the
centromere, q arm, p arm, and telomere. Illustrate the different types of structural
mutations that occur in chromosomes. Show how karyotypes reveal chromosomal
abnormalities. Describe interphase and metaphase FISH
analyses.
Mutation: a permanent transmissable change in the genetic material, usually in a single gene
Polymorphism: two or more genetically determined, proportionally represented phenotypes in the same population
Mutations and PolymorphismsMutations and Polymorphisms
Types of MutationsTypes of Mutations
Genomic: abnormal chromosome number (monosomy, polysomy, aneuploidy)
Chromosomal: abnormal chromosome structure
Gene: DNA sequence changes in specific genes
Chromosome MorphologyChromosome Morphology
Telomere: chromosome ends
Centromere: site of spindle attachment Constriction of the
metaphase chromosome at the centromere defines two arms
Nucleosome: DNA double helix wrapped around histone proteins
Centromere
Telomere
Metacentric Submetacentric Acrocentric
Telomere
Arm
Longarm (q)
Shortarm (p)
Chromosome MorphologyChromosome Morphology
p
q
Arm Region Band Subband
2
1
1
2
21
1
12
3
4
3212154321
12
312312, 34123
17q11.2
Chromosome 17
Defining Chromosomal LocationDefining Chromosomal Location
Chromosome Morphology Changes Chromosome Morphology Changes During the During the Cell Division Cycle.Cell Division Cycle.
DNA double helix: 2nm diameter Interphase (G1, S, G2)
Chromatin “beads on a string:” 11nm Chromatin in nucleosomes: 30nm
Metaphase (Mitosis) Extended metaphase chromosomes: 300 nm Condensed metaphase chromosomes: 700 nm
Cell Division CycleCell Division Cycle
G1 S
G2
Interphase(11–30 nm fibers)
Metaphase(300–700 nm fibers)
MMitosis:ProphaseAnaphaseMetaphaseTelophase
Visualizing Metaphase Visualizing Metaphase ChromosomesChromosomes
Patient cells are incubated and divide in tissue culture.
Phytohemagglutinin (PHA): stimulates cell division
Colcemid: arrests cells in metaphase 3:1 Methanol:Acetic Acid: fixes
metaphase chromosomes for staining
Visualizing Metaphase Visualizing Metaphase Chromosomes (Chromosomes (BandingBanding))
Giemsa-, reverse- or centromere-stained metaphase chromosomes
G-Bands R-Bands C-Bands
KaryotypeKaryotype
International System for Human Cytogenetic Nomenclature (ISCN) 46, XX – normal female 46, XY – normal male
G-banded chromosomes are identified by band pattern.
Normal Female Karyotype (46, XX)Normal Female Karyotype (46, XX)(G Banding)(G Banding)
Normal Female KaryotypeNormal Female Karyotype(High-Resolution G Banding)(High-Resolution G Banding)
Chromosome Number AbnormalityChromosome Number AbnormalityAneuploidy (48, XXXX)Aneuploidy (48, XXXX)
Chromosome Number AbnormalityChromosome Number AbnormalityTrisomy 21 (47, XX, +21)Trisomy 21 (47, XX, +21)
Translocation Deletion
Insertion
Inversion Isochromosome
Ringchromosome
Derivativechromosome
Chromosome Structure Chromosome Structure AbnormalitiesAbnormalities
Chromosome Structure Abnormality:Chromosome Structure Abnormality:Balanced Translocation 45, XY, t(14q21q)Balanced Translocation 45, XY, t(14q21q)
Probe
Interphase or metaphasecells on slide (in situ)
Microscopicsignal (interphase)
Fluorescent Fluorescent in situin situ Hybridization Hybridization (FISH)(FISH)
Hybridization of complementary gene- or region-specific fluorescent probes to chromosomes.
Fluorescent Fluorescent in situin situ Hybridization Hybridization (FISH) (FISH)
Metaphase FISH Chromosome painting Spectral karyotyping
Interphase FISH
Uses of Fluorescent Uses of Fluorescent in situin situ Hybridization (FISH)Hybridization (FISH)
Identification and characterization of numerical and structural chromosome abnormalities.
Detection of microscopically invisible deletions.
Detection of sub-telomeric aberrations. Prenatal diagnosis of the common
aneuploidies (interphase FISH).
FISH ProbesFISH Probes
Chromosome-specific centromere probes (CEP) Hybridize to centromere region Detect aneuploidy in interphase and metaphase
Chromosome painting probes (WCP) Hybridize to whole chromosomes or regions Characterize chromosomal structural changes in metaphase
cells Unique DNA sequence probes (LSI)
Hybridize to unique DNA sequences Detect gene rearrangements, deletions, and amplifications
Telomere
(TTAGGG)n
100–200 kb 3–20 kbUnique sequences Telomere associated repeats
Probe binding site
FISH ProbesFISH Probes
Telomere-specific probes (TEL) Hybridize to subtelomeric regions Detect subtelomeric deletions and
rearrangements
Normal diploid signal
Trisomy or insertion
Monosomy or deletion
Cellnucleus
Genetic Abnormalities by Genetic Abnormalities by Interphase FISH LSIInterphase FISH LSI Probe Probe
Greater or less than two signals per nucleus is considered abnormal.
Structural Abnormality by Interphase Structural Abnormality by Interphase FISH LSIFISH LSI Probe ( Probe (Fusion ProbeFusion Probe))
Structural Abnormality by Interphase Structural Abnormality by Interphase FISH LSIFISH LSI Probe ( Probe (Break Apart ProbeBreak Apart Probe))
Translocation by Metaphase FISHTranslocation by Metaphase FISHWCP Probe (WCP Probe (Whole-Chromosome PaintingWhole-Chromosome Painting))
SummarySummary
Mutations are heritable changes in DNA. Mutations include changes in chromosome number,
structure, and gene mutations. Chromosomes are analyzed by Giemsa staining and
karyotyping. Karyotyping detects changes in chromosome number
and large structural changes. Structural changes include translocation, duplication,
and deletion of chromosomal regions. More subtle chromosomal changes can be detected by
metaphase or interphase FISH.