NORMAL KARYOTYPE Karyotype: a picture of the chromosomes from a single cell.
International system forhuman cytogeneticnomenclature.eg- Xp21.2Eg-47,XY,+21
NUMERICAL ABNORMALITIES Euploid-any exact multiple of haploid Aneuploidy-chromosome compliment that is not an exact mutiple of 23 Nondisjunction Anaphase lag Mosaicism-mitotic error in early development give rise to 2 /more population of cells with different chromosomal complement in some individual EG-45X/47XXX mosaic
STRUCTURAL ABNORMALITIES Deletions-loss of a portion of chromosome Eg-46,XY,del(16)(p11.2p13.1)
SPONTANEOUS ABORTIONS 1 in 200 live born children is chromosomally abnormal 95% of chromosomally abnormal conceptus are aborted spontaneously Abortion mostly occurs in 1st trimester
DOWN SYNDROME Incidence-1 in 700 95% have trisomy 21,chromosome no 47 1% cases are mosaics.-mitotic nondisjunction 4% cases-extra chromosomal material derives from presence of robertsonian translocationof long arm of chromosome 21 to acrocentric chromosome. 10 to 20 fold increased risk of deveoping leukemia
CHROMOSOME 22q11.2 DELETION SYNDROME Small deletion of band q11.2 on long arm of chromosome 22. 1 in 4000 births Congenital heart defects ,palatal abnormalities, facial dysmorphism, developmental delay,T-cell immunodeficiency and hypocalcemia High risk for schizophrenia and bipolar disorder
TRISOMY 18 Incidence 1/8000 Overlaps with trisomy 13 Sever Mental retardation >90% dead in 1st year Small face with prominant occiput Small sternum and pelvis Flexion deformity of the finger VSD and horseshoe kidney
TRISOMY 13(PATAU SYNDROME) Severe developmetal retardation Incidence 1/20000 90% dead in the 1st year Midline brain defect Malformed ear Micropthalmos and coloboma Scalp defect
CYTOGENETIC DISORDERS AFFECTING SEXCHROMOSOME More common than autosomal aberrations. Lyon hypothesis
TURNER SYNDROME Complete or partial monosomy of X chromosome Hypogonadism in phenotypic females 1 in 2000 live born females 57% missing an entire X chromosome-45,X karyotype 14% have structural abnormalities of X chromosome 29% are mosaics Structural abnormalities are- Deletion of small arm-isochromosome of long arm-46,X,i(X)(q10) Deletion of portion of both long and short arms-ring chromosome-46,X,r,(X) Deletion of portion of short or long arm-46X,del(Xq) Mosaic patterns- 45,X/46,XX 45,X/46,XY 45,X/47XXX 45,X/46,X,i(X),(q10)
KLINEFELTER SYNDROME Male hypogonadism occur when there are 2 /more X chromosome and one /more Y chromosome. 1 in 660 live male births Eunuchoid body habitus,abnormally long legs,small atrpohic testis,lack of secondary male characteristics Increased incidence of type 2 diabetes,metabolic syndrome Higher risk of breast cancer,extragonadal germ cell tumor and autoimmune diseases 47,XXY-90% cases 15% cases are mosaics
HERMAPHRODITISM GENETIC SEX PHENOTYPIC SEX PSEUDOHERMAPHRODITISM TRUE HERMAPHRODITISM FEMALE PSEUDOHERMAPHRODITISM-excessive and innapropriate exposure to androgenic steroids during early gestation MALE PSEUDOHERMAPHRODITISM-extremely heterogenous.most common –defective virilization of male embryo(complete androgen insensitivity syndrome)
KARYOTYPING 3 main methods to identify chromosomes G BANDING-------giemsa Q BANDING-------quinacrine R BANDING-------reverse
SUBCLASSIFICATIONS OF BANDING METHODSISCN 1985 3 letter code to describe banding techniques. Ist letter---type of banding 2nd letter—general technique 3rd letter—the stain Eg-QFQ------Q band by flourescence using quinacrine
G BANDING System of dark and light bands throughout the euchromatin part of chromosome Staining technique where chromosomes are treated with trypsin then with giemsa stain Needs metaphase Culture cells until sufficient mitotic activity Add colchicine to arrest in metaphase
TERMS AND DEFINITIONS OF VARIOUS ABERRATIONS OFCHROMOSOMES Ring( r) Dicentric(d) Hyperdiploid (h) Chromosome gap (sg) Chromatid deletion (td) Fragment (f) Acentric fragment (af) Translocation (t) Triradial (tr) Quadriradial (qr) Complex rearrangement (cr) Polyploid (pp) or endoreduplication
FLOURESCENT IN SITU HYBRIDISATION(FISH) Fluorescence in situ hybridization (FISH) uses fluorescent molecules to ―paint‖ genes or chromosomes. This technique is for gene mapping, identification of chromosomal abnormalities FISH involves the use of short sequences of single-stranded DNA (probes) which are labeled with fluorescent tags, to hybridize, or bind, to the complementary DNA to see the location of those sequences of DNA under the fluorescent microscope.
ADVANTAGES OF FISH Rapid High efficiency of hybridization and detection Lots of cells can be analyzed Cells do not have to be replicating
SPECTRAL KARYOTYPING Chromosomal and subchromosomal painting probes that make use of sorted or microdissected chromosomes
Mixtures of fluorophores used to separately label chromosome-specific probesThese are mixed and hybridized en masse Interpreted via spectral interferometerTremendously useful in detecting insertions and translocations,especially in cancers.