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Chromosomal Abnormalities. Jane Yoo HST.180 January 27, 2004. Genetic Disorders. Cytogenetic Disorders Gross chromosomal abnormalities Single Gene Disorders Classical (Mendelian) inheritance Non-classical inheritance Mitochondrial genes Trinucleotide repeats

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chromosomal abnormalities

Chromosomal Abnormalities

Jane Yoo


January 27, 2004

genetic disorders
Genetic Disorders
  • Cytogenetic Disorders

Gross chromosomal abnormalities

  • Single Gene Disorders

Classical (Mendelian) inheritance

Non-classical inheritance

Mitochondrial genes

Trinucleotide repeats

Genetic imprinting

Cytogenetic disorders are characterized by an abnormal constitutional karyotype

What mechanisms would result in cytogenetic abnormalities?

chromosomal rearrangments
Chromosomal Rearrangments
  • Translocation
  • Deletion
  • Duplication
  • Inversion
trisomy 21 down syndrome
Trisomy 21 (Down Syndrome)
  • The most common chromosomal disorder with an incidence of 1:700 live births in the US
  • 95% trisomy 21; 4% Robertsonian translocation involving long arm of 21; 1% mosaic
  • High correlation between maternal age and meiotic nondisjunction leading to trisomy 21
  • Congenital heart disease; dysmorphic features; mental retardation; predisposition to leukemias; neurodegenerative changes; abnormal immune response and autoimmunity
patient interview
Patient Interview

Chromosome 2

2p25.3 myelin transcription factor 1-like

2p21 protein kinase C, epsilon

2p12-p11.1 catenin (cadherin-associated protein), alpha 2

2q14.3 caspr5 protein

2q21.2 low density lipoprotein-related protein 1B (deleted in tumors)

2q22.3 Rho GTPase activating protein 15

2q31.1-q31.2 myosin IIIB

2q33.3 amyotrophic lateral sclerosis 2 (juvenile) chromosome region, candidate 19

single gene mendelian disorders
Single Gene Mendelian Disorders
  • Structural Proteins

--Osteogenesis imperfecta and Ehlers-Danlos (collagens); Marfan syndrome

(fibrillin); Duchenne and Becker muscular dystrophies (dystrophin)

  • Enzymes and Inhibitors

--Lysosomal storage disease; SCID (adenosine deaminase); PKU

(phenylalanine hydroxylase); Alpha-1 antitrypsin deficiency

  • Receptors

--Familial hypercholesterolemia (LDL receptor)

  • Cell Growth Regulation

--Neurofibromatosis type I (neurofibromin); Hereditary retinoblastoma


  • Transporters

--Cystic Fibrosis (CFTR); Sickle Cell (Hb); Thalassemias (Hb)

genetic imprinting
Genetic Imprinting
  • For most (non-imprinted) genes, the maternal copy is functionally equivalent to the paternal copy
  • Imprinted genes, however, are expressed differently from maternal and paternal alleles
  • In most cases, imprinting selectively inactivates either the maternal or the paternal allele of a particular gene
the puzzle of del 15 q11q13
The Puzzle of Del(15)(q11q13)

Mental Retardation Mental Retardation

Ataxic gait Short Stature

Seizures Hypotonia

Inappropriate laughter Obesity


fluoresence in situ hybridization fish
Fluoresence In Situ Hybridization (FISH)
  • Fluorescent molecules paint
  • chromosomes to detect abnormalities
  • Labeled probes hybridize to complementary DNA
  • Three types of probes: locus specific, centromeric repeat, whole chromosome
fish many varieties
FISH: Many Varieties

Multicolor FISH

Spectral Karyotyping

Comparative Genomic Hybridization (CGH)

interphase fish
Interphase FISH
  • Provides analysis of chromosomal aneuploidy from direct amniocyte or chorionic villus sample (CVS) preparations
  • Screens for abnormalities in Chromosomes X, Y, 13, 18, 21

which account for 70% of chromosomal aneuploidy in the second trimester

  • Subtelomeric probes allow for screening of terminal rearrangements
cytogenetics and fish
Cytogenetics and FISH
  • Interphase FISH was performed on direct CVS or amniocyte preparations from 12 reciprocal translocation and 2 Robersonian translocation pregnancies
  • Hybridization involved 1:1 mixture of Spectrum Green labeled pter subtelomere and Spectrum Orange qter subtelomere probes
  • Fifty interphase nuclei were scored
prenatal preimplantation genetic diagnosis pgd
Prenatal & Preimplantation Genetic Diagnosis (PGD)
  • Involves creation of several in vitro embryos from the eggs and sperm of a couple
  • Embryos develop to a 6-10 cell stage, at which point one of the embryonic cells is removed and the cellular DNA is analyzed for chromosomal abnormalities
  • Embryos free of genetic abnormalities are subsequently transferred to women’s uterus for gestation. Embryos found carrying a genetic abnormality are discarded.
ethical social implications of pgd
Ethical & Social Implications of PGD
  • PGD has been used in several countries for sex selection
  • Designer baby eugenics
  • Creating babies to save siblings from a life-threatening disease