Histology Lecture (6) Karyotyping PDF

Histology lecture (6) karyotyping Histology karyotyping Definitions  Study of number & morphology (shape) of chromosomes of the Karyotyping individuals.  Map of complete set of chro...

Histology lecture (6) karyotyping Histology karyotyping Definitions  Study of number & morphology (shape) of chromosomes of the Karyotyping individuals.  Map of complete set of chromosomes of an individual, arranged as Karyotype homologous pairs according to their length.  Histology How to write a person's karyotype Total number of chromosomes, followed by sex chromosomes. Normal male karyotype → 46, XY. Normal female karyotype → 46, XX. Shorter arm → p. Longer arm → q. Normal morphology of chromosomes Morphology of metaphase chromosome  Each chromosome (d-chromosome) is made of 2 identical halves called sister chromatids, which are joined at primary constriction known as the centromere.  Each chromatid consists of a tightly coiled molecule of DNA.  The terminal end of the chromatidis called telomere which : Is a repeated DNA sequences added by telomerase enzyme. It protects and stabilizes the end of the chromosome.  Diploid cells are called so because each cell contains two copies of every chromosome.  A pair of such chromosomes is called a homologous pair.  In a homologous pair of chromosomes : One homologue originates from maternal parent. The other from the paternal parent.  Histology  In humans, there are 46 chromosomes (23 homologous pairs).  In males, there are only 22 homologous pairs (autosomes) and one non homologous pair— the sex chromosomes of X and Y.  Some chromosomes have a secondary constriction, on upper arms (chromosomes: 13, 14, 15, 21 & 22).  The terminal portion is called a satellite. Histology Chromosomal Anomalies Definitions Deviation from the normal number or morphology (shape) of chromosomes. May affect autosomes or sex chromosomes. Types Numerical (abnormal number). Structural (abnormal shape). Turner’s Wolf syndrome Klinefelter’s syndrome Down’s syndrome Cri –du-chat syndrome Multiple X Philadelphia chromosome YY syndrome syndrome Causes 1. Radiation. 2. Infection with German measles. 3. Pregnancy in old age. 4. Autoimmune diseases. 5. Family history of chromosomal abnormalities. Histology A Numerical aberrations of sex chromosomes 1. Klinefelter’s syndrome 2. YY syndrome  A condition in which a male has an  A condition in which a male has an Def extra X chromosome (i.e. XXY) in extra Y chromosome (i.e. XYY) in his cells. his cells.  47, XXY  47, XYY Karyotype  48, XXXY  49, XXXXY 3. Turner’s syndrome 4. Multiple X syndrome  A condition in which a female has  A condition in which a female has Def only one X instead of XX in her cells an extra X chromosome (i.e. XXX) in her cells.  45, XO  47, XXX Karyotype  48, XXXX  49, XXXXX  A condition in which there is an extra chromosome 21 in each cell i.e. trisomy.  Most common chromosomal abnormality. Def  47, XY+21 (male). Karyotype  47, XX+21 (female) Histology B Structural chromosomal aberrations Wolf syndrome Cri-du-chat syndrome Partial deletion of the short Partial deletion of the short Cause : arm of chromosome no. 4. arm of chromosome no.5. Karyotype : Male 46, XY, 4p- 46, XY, 5p- Female 46, XX, 4p- 46, XX, 5p- Philadelphia chromosome (PH) Translocation of half of the long arm of Cause chromosome no. 22 to chromosome no. 9. Karyotype 46, XX (or XY) , t (9 ; 22)