Lecture 45: Karyotyping And Aneuplody Flashcards
How can structural chromosomal abnormalities arise?
1) Deletion
2) Duplication
3) Inversions
4) Translocations
5) Isochromosomes
6) Ring chromosomes
How can we get the wrong number of chromosomes?
1) Non-disjunction (Meiosis or mitosis)
2) Mosaicism
What is cytogenetic testing and how do we do it?
- Karyotyping, giemsa staining
- FISH
- MGH Microarray
Process:
1) Blood sample
2) Add phytohemagglutinin which makes blood cells/lymphocytes divide
3) Add Colchinine which arrests dividing cells in metaphase
4) Cells swollen in hypertonic solution
5) Stain, spread on slide, observe w microscope
Karyotyping
- Use microscope
- Only views large altercations- > 5Mb (Small wont change banding, like microdeletions)
Detects
-deletions, duplications, inversions, translocations, etc.
Chromosomes:
Metacentric
Submetacentric
Acrocentric
Metacentric
-P and Q arm equal
Submetacentric
-P < Q
Acrocentric
- P arm basically non existent
- Satellites attached
What does FISH detect
- Needs correct probe to function
- Deletions needs to be larger than probe to be detected
Detects:
- # chrom abnormalities
- Deletions
- Translocations
- Gene amplifications (cancer)
- Micro-deletions (Unlike karyotyping bc has higher resolution)
Stages FISH can be held in
Interphase Stage:
(Rapid test)
-Avoids cell culture
-Chromosomes decondensed in nucleus
Metaphase Stage:
- Cultures cells
- Usually done after G-band karyotyping
- GIves location info bc the banding pattern in known
Method of SKY FISH and what does it detect?
-Chromosome painting (Each chromosome probed with fluorescence color= all glow diff color)
Detects:
-Translocations
Uses:
-Cancer
Euploidy (Polyploidy) Chromosomes:
1) Diploidy
2) Triploidy
3) Tetraploidy
Aneuploidy:
1) Monosomy
2) Trisomy
-Euploidy = chromosome # in multiples of 23
- Diploidy: Normal = two per pair = 46
- Triploidy: Abnormal = 3 per pair = 69 (Can’t survive)
- Tetraploidy: Abnormal= 4 per pair = 92 (Can’t survive)
- Aneuploidy: (Not multiple of
1) Monosomy = loss of chromosome = (Turners Monosomy X only one compatible with life) - Can only survive with 45, X arrangement)
2) Trisomy= extra chromosome - (Ex: XXY)
Trisomy 21
Cause
Risks
Symptoms
Karyotyping
-Downs syndrome
Cause:
- Meiosis nondisjunction I or II maternal
- Robertsonian translocation
- Mosaic children
Risks:
-Increased maternal age
Symptoms:
- Intellectual delay
- Short stature
- Depressed nasal bridge/upslanted palpebral fissures
- Single palmar crease
Karyotyping:
- FISH probes in interphase = rapid results
- 2 chrom = 13 signals and green
- 3 chrom = 21 signals and red
- Prenatal diagnosis with maternal serum screening and ultrasound
Trisomy 18
Symptoms
Karyotyping
-Edward Syndrome
Cause
-Nondisjunction during oogenesis
Symptoms:
- Clenched fist, overlap fingers
- Rocker bottom feet
- Congenital heart defects
- Low-set ears, small lower jaw
- Microcephaly
- Intellectual disability
Karyotyping:
- FISH probes (interphase for rapid) = 3 chrom, 18 signals
- Array CGH shows all trisomy 18
Trisomy 13
Symptoms
Karyotyping
-Patau Syndrome (47, XX, +13)
Cause:
-Nondisjunction during oogenesis
Symptoms:
- Polydactyly
- Cleft lip and palate
- Microphthalmia
- Microcephaly
- Intellectual disability
- Cardiac anomalies (VSD or ASD)
Karyotyping:
-FISH (Interphase) = rapid
Array CGH will show trisomy 13
Turner Syndrome (45, X)
-FEMALES HAVE NO BARR BODY (Inactivation of X-Chrom)
Turner Syndrome (45, X):
- X chrom monosomy (only have moms ish)
- Nondisjunction in SPERMATOGENESIS
- Symptoms:
1) Webbed/swollen neck
2) Lymphoedema of hands and feet
3) Amenorrhea
4) Streak ovaries
5) Gondal dysgenesis
Mosaic Turner Syndrome
Some Females can be mosaic for Turners
- 46, XX
- Mitotic-Nondisjunction (Embryogenesis)
- Some cells 45, X and 46, XX and 47 XXX
Some Females phenotypic females are mosaic:
- 46, XY
- Mosaic 45, X and others 46, XY (recommended oophorectomy due to risk of gonadlastoma)
Klinefelter Syndrome (47, XXY)
Mosaic individuals:
- 46XY
- 47 XXY
- 48 XXXY
-Have a Barr Body
Characteristics:
- Gynecomastia
- Female distribution of hair
- Infertility and testicular atrophy due to low levels of testosterone
- Feminization of features
-FISH probes, Array CGH, Karyotype can detect it’s extra chromosomes
