Humman Chromosomes Histology Lecture PDF

HUMMAN CHROMOSOMES By Mona Abd-elmawla Soliman Assistant Prof. of histology Faculty of medicine Menoufia university Intended learning outcome ✓Describe the structure of chromosome. ✓Define chromosomal abnormalities. ✓Identify types of structural chromosomal abno...

HUMMAN CHROMOSOMES By Mona Abd-elmawla Soliman Assistant Prof. of histology Faculty of medicine Menoufia university Intended learning outcome ✓Describe the structure of chromosome. ✓Define chromosomal abnormalities. ✓Identify types of structural chromosomal abnormalities. ✓Identify types of numerical chromosomal abnormalities. ✓Correlate between chromosomal abnormalities and its clinical applications. ✓Define Barr body and outline its clinical applications.  General Characteristics - Chromosomes are the carriers of genetic information, as they contain the genes, which are the units of heredity. - They are formed of macro-molecules of DNA, in the form of two strands, twisted on each other, in the form of double helix. - Human somatic cells contain diploid number of chromosomes (46 = 44 autosomes & 2 sex chromosomes). - Male cells contain XY sex chromosomes, while female cells contain XX sex chromosomes.  Structure of chromosome Each chromosome is made of two chromatids (sister chromatids), connected at the centromere. Centromere divides chromosomes into 2 arms, short arm (p) and long arm (q). The centromere divides the chromatid into 2 arms; short upper arm (P arm) and long lower arm (Q arm). Structure of chromosome  Chromosomal abnormalities Definition: It is disturbance in chromosomal structure and number. Causes of Chromosomal abnormalities: ✓ Hereditary in the family. ✓ Old age pregnant women. ✓ Infection with German measles during pregnancy. ✓ Exposure of pregnant women to radiation or autoimmune disease.  Types of chromosomal abnormalities ❑Abnormalities of structure: These are changes in morphology or structure of chromosomes. 1-Deletion: is loss of a part of one or more chromosome. 2-Breaks of chromosomes & ring formation. 3- Inversion: is wrong reattachment of broken segments of chromosomes. 4- Translocation: is the transfer of segments between chromosomes. 5- Iso-chromosomes: is abnormal transverse division of the centromere separating the two arms instead of longitudinal division separating individual chromatids.  Deletion loss of a part of one or more chromosome  Ring chromosome Breaks of chromosomes & ring formation  Inversion Wrong reattachment of broken segments of chromosomes.  Translocation is the transfer of segments between chromosomes  Iso-chromosome is abnormal transverse division of the centromere separating the two arms instead of longitudinal division separating individual chromatids.  Numerical chromosomal abnormalities ❑These are changes in number by addition or loss of one or more of chromosomes.  Numerical chromosomal abnormalities ✓Polyploidy: is abnormal duplication of haploid number of chromosomes. Normally the number of chromosomes in somatic cells is double the haploid number (2n). Triploidy it is 3 times the haploid number (3n)  Numerical chromosomal abnormalities Tetraploidy it is 4 times the haploid number (4n). ✓These numerical aberrations are incompatible (impossible to continue) with life & cause miscarriage (loss of pregnancy).  Numerical chromosomal abnormalities ✓Aneuploidy: is the addition (Triosomy) or loss (Monosomy) of a chromosome and may affect autosomes or sex chromosomes.  Aneuploidy of autosomes ✓ Triosomy: is the presence of an additional chromosome to the usual pairs. It has been reported in all autosomes except chromosome number 1. The commonest is trisomy 21, which means the presence of 3 of chromosome (21) in Down’s syndrome or Mongolism. ✓ Monosomy: is the missing of one chromosome from the usual pairs and it is lethal.  Down syndrome The characteristics of Down syndrome include low muscle tone, short stature, a flat nasal bridge, a protruding tongue, small hands and feet, and skin fold in the inner corner of eyes. People with Down syndrome have a higher risk of some conditions, including Alzheimer’s disease and epilepsy.  Down syndrome Doctors can use screening tests during pregnancy to estimate the probability that a child will have Down syndrome.  Aneuploidy of sex chromosomes ✓ Triosomy: is presence of an additional sex chromosome (usually X). Normally, males have X & Y sex chromosomes and need both for sex differentiation, while female cells possess double X chromosomes, one is inactive called sex chromatin or Barr body, and so females are positive for sex chromatin, while males are negative.  Aneuploidy of sex chromosomes Klinefilter syndrome: In this disease males have positive sex chromatin (47, XXY) presenting with poor musculature, underdeveloped genitalia, infertility and gynecomastia. They have higher risk for breast cancer.  Aneuploidy of sex chromosomes ✓ Monosomy of X chromosome is detected in females (45, X0) in Turner syndrome. ✓ Turner syndrome: gonadal dysgenesis is a common abnormality, where one X chromosome is missing. Barr body is absent. In this disease females have primary amenorrhea, underdeveloped genitalia and secondary sex characters, infertility, together with renal and cardiac anomalies.  Sex chromatin (Barr body) ✓ The sex chromatin represents an X chromosome, which remains inactive (coiled), during the interphase, stained with basic dyes (Hx) and is Feulogon +ve. ✓ It occurs in females as their cells posses double X chromosomes, while males have Y & X sex chromosomes and need both for sex differentiation as sperms contain either Y or X sex chromosome, while ova contain X sex chromosome.  Sex chromatin (Barr body) ✓Somatic female cells as those lining the internal surface of cheek show a darkly stained body or granule, at the periphery of their nuclei attached to the nuclear envelope (sex chromatin or Barr body). ✓In neutrophils, it appears as a drum-stick like structure, attached to the nucleus. Sex chromatin (Barr body) Sex chromatin (Barr body) Sex chromatin (Barr body) Sex chromatin (Barr body)  Importance of Barr body 1. Identification of the sex of fetus. 2. Diagnosis of chromosomes abnormalities. 3. Diagnosis of the cause of primary amenorrhea, repeated abortion, sterility. 4. Important for forensic medicine and Olympic games Q: Which one of the following represent missing of one chromosome? a) Monosomy. b) Nulliosomy c) Trisomy. d) Tetrasomy. Q: which one of the following represents the main cause of Down syndrome? a) Trisomy of 21st chromosome. b) Tetrasomy of 21st chromosome. c) Trisomy of 22nd chromosome. d) Tetrasomy of 22nd chromosome. THANK YOU