7-Cytogenetics.pdf

Cytogenetics Dr Somaya Elbushra Mohammed MBBS-MSc- MHPE Dr Somaya Elbushra 1  Normal chromosome Human somatic cells have 23 pairs of chromosomes (46) 22 pair of autosomes + 2 sex chromosomes (44,XX) or (44,XY). Gametes have 23 chromosomes....

Cytogenetics Dr Somaya Elbushra Mohammed MBBS-MSc- MHPE Dr Somaya Elbushra 1  Normal chromosome Human somatic cells have 23 pairs of chromosomes (46) 22 pair of autosomes + 2 sex chromosomes (44,XX) or (44,XY). Gametes have 23 chromosomes. Dr Somaya Elbushra 2  Normal chromosome Centromere Chromosomes are classified according to centromere location into: Dr Somaya Elbushra 3 Karyotype : is an individual's complete set of chromosomes Dr Somaya Elbushra 4 Chromosome banding refers to alternating light and dark regions along the length of a chromosome, produced after staining with a dye Dr Somaya Elbushra 5  Chromosomal abnormalities Chromosomal abnormalities (CAs) are seen in 50% of spontaneous fetal losses during the first trimester of pregnancy, CAs one of the causes of congenital malformations. Types of chromosomal abnormalities: (a) Numerical (b) Structural Dr Somaya Elbushra 6  Numerical Chromosomal Abnormalities Changes in the number of chromosomes: Euploidy Somatic cells contain multiples of number of chromosome sets (haploid number = n) 3n (69 ch) , 4n (92 ch). Aneuploidy: Deviation from the diploid number of chromosomes (2n + 1), (2n -1) etc. Dr Somaya Elbushra 7  Types of Aneuploidy: A)Trisomy: presence of three copies of a chromosome in your somatic cells. B) Monosomy: one copy of a chromosome in your somatic cells. Both may involve autosomes or sex chromosomes Non-dysjunction: failure of separation of chromosomes during cell division. Formation of 2 abnormal types of gametes Dr Somaya Elbushra 8 Dr Somaya Elbushra 9 Dr Somaya Elbushra 10 Aneuploidy in sex chromosomes: 1. Turner syndrome (45,XO) X0 female Dr Somaya Elbushra 11 Aneuploidy in sex chromosomes: 2. Klinefelter syndrome XXY male often not detected until puberty, infertile. Dr Somaya Elbushra 12 4. XXX female (triple X syndrome): Learning disabilities. Tall stature, Low muscle tone (hypotonia) occasionally, infertility Dr Somaya Elbushra 13 3. XYY syndrome:(Jacob’s syndrome): A male is usually tall, with mild mental retardation and aggressiveness; Normal sexual development and fertile. weaker muscle tone. learning difficulties or speech problems. Dr Somaya Elbushra 14  Autosomal aneuploids: generally, tend to be spontaneously aborted Trisomy 13 (Patau Syndrome): Chromosomal set: 47,XX,+13 (female) or 47,XY,+13 (male) Dr Somaya Elbushra 15 Trisomy 21 (Down Syndrome): Chromosomal set: 47,XX,+21 (female) 47,XY,+21 (male) Dr Somaya Elbushra 16 ▪ Trisomy 18 (Edward syndrome): Chromosomal set: 47,XX,+18 47,XY,+18 Dr Somaya Elbushra 17  Structural Chromosomal Abnormalities Deletions in Humans: Cri-du-chat syndrome – Micro deletion of chromosome 5 – Characteristic cat-like cry, which disappears with age – Microcephaly and severe mental retardation Di-George syndrome – Micro deletion of chromosome 22 Angelman syndrome & Prader-Willi syndrome – Micro deletion of chromosome 15 Dr Somaya Elbushra 18  Duplication: Example is Fragile X syndrome on chromosome Xq27 Dr Somaya Elbushra 19 Translocation: The extra chromosome 21 or part of it is attached to another chromosome (Down syndrome) Dr Somaya Elbushra 20