Chapter 3 ( Cytogenics ) Flashcards
G banding ?
Mitotic chromosomes are partially digested with trypsin and then stained with Giemsa
Acrocentric chromosomes ?
13-14-15-21-22
Which are the only chromosomes involved in Robertsonian translocation
Autosomal monosomies ?
All are inconsistent with a live birth
Autosomal trisomies ?
Only 3 are consistent with a live birth which are : 13 - 18 - 21
Down syndrome ?
Trisomy 21 Mental retardation Short stature Hypotonia Depressed nasal bridge Upslanting palpebral fissure , epicanthal fold Congenital heart defects Reduced fertility
Edward syndrome ?
18 trisomy Clenched fist with overlapping fingers Low set ears Micrognathia Mental retardation Inward turning Congenital heart defects
Patau syndrome ?
Trisomy 13 Polydactyly Cleft lip and cleft palate Microphthalmia Microcephaly and mental retardation Cardiac and renal defects
Klinefelter syndrome ?
Sex chromosome aneuploidy 47,XXY Testicular atrophy Infertility Gynecomastia Female distribution of hair High pitched voice
Turner syndrome ?
The only monosomy consistent with life
45,X
50% of cells are 45,X
Majority of others are mosaics for 45,X and one other cell lineage
Short stature
Cystic hygroma in utero resulting in excess nuchal skin and webbed neck
Primary amenorrhea
Infertility
Edema of wrist and ankles in new borns
Coarctation of aorta and other congenital heart defects
Prenatal triple screen ?
Prenatal screening for down syndrome by assessing the serum levels of
1- alpha fetoprotein
2- chorionic gonadotropin
3- unconjugated estriol
Which can detect 70% of fetuses with down
Types of chromosomal translocations ?
1- Reciprocal translocation : when genetic material is exchanged between two homologous chromosomes .
2- Robertsonian translocation : occurs only in acrocentric chromosomes and involves loss of short arms of two of the chromosomes and subsequent fusion of the long arms .
Alternate and adjacent segregation ?
Alternate segregation : chromosomes from alternate quadrants enter a gamete
Adjacent segregation : chromosomes from adjacent quadrants enter a gamete
Reciprocal translocations involving oncogenes ?
t(9;22) Chronic myelogenous leukemia (c-abl)
t(8;14) Burkitt lymphoma (c-myc)
t(15;17) Acute myelogenous leukemia (retinoid recepor alpha)
t(14;18) Follicular lymphomas (bcl-2 that inhibit apoptosis)
t(11;14) Mantle cell lymphoma (cyclin D)
Cri-du-chat syndrome ?
Caused by interstitial or terminal deletion of 5p ( short arm of chromosome 5 )
High-pitched cat like cry
Microcephaly and mental retardation
Congenital heart disease
Examples for microdeletions ?
Parder-Willi syndrome Angelman syndrome DiGeorge syndrome Wilms tumor Williams syndrome
Williams syndrome ?
Hypercalcemia
Supravalvular aortic stenosis
Mental retardation
Characteristic face
DiGeorge syndrome ?
Congenital absence of the thymus and parathyroids Hypocalcemic tetany T-cell immunodeficiency Characteristic face with cleft palate Heart defects
The only example for isochromosome that’s compatible with live birth ?
Turner syndrome 46,X,i(Xq)
Which is the cause of 22% of Turner cases
The other 78% have 45,X monosomy due to nondisjunction
Fluorescence in situ Hybridization (FISH) uses and advantages ?
Used to detects ; aneuploidies , translocations , deletions
Advantage : the chromosomes don’t have to be in the metaphase stage for accurate diagnosis
Uses of Spectral Karyotyping ?
Visualization of chromosome rearrangements such as small translocations
Example : Philadelphia chromosome rearrangement t(9;22) in CML
Direct genetic testing and indirect genetic testing types ?
Direct genetic testing :
1- PCR and ASO probes
2- RFLP analysis of PCR product
3- Direct DNA sequencing
Indirect genetic testing :
1- using STRPs
2- using RFLPs
