Give an account of the chromosomal disorders in human with reference to Downs syndrome Klinefelters syndrome and Turners syndrome

Chromosomal disorders in human with reference to Down’s syndrome, Klinefelter’s syndrome and Turner’s syndrome.

 
Down’s syndrome (21-trisomy) Mongolism                                                  
Down’s syndrome is one of the most common chromosome abnormalities of man. It was first reported by Langdon Down. It is an autosomal aneuploidy caused by the presence of an extra chromosome 21. during normal oogenesis a chromosome of the pair 21 enters an ovum. But due to nondisjunction of chromosomes of pair 21 during meiosis the chromosome of pair 21 pass into a single ovum. Thus, the ovum possesses 24 chromosomes instead of 23 chromosomes. When they form zygote with a sperm and the offspring has 23 + 23+1 =47 chromosomes. In female it is 45+XX in male 45+XY. Down’s syndrome symptoms:  They have broad forehead, short and broad neck, short and stubby (short and thick) fingers permanently open mouth, protruding tongue, projecting lower lip, flat hands, severe mental retardation hear, and other organs may be defective, gonads and genitalia are underdeveloped. Women around 45 years of age are more likely to produce children having Down’ syndrome. 
Turner’s syndrome                                                                                  
Henry H. Turner first describe this genetic disorder. The chromosome number is 45 (44+X0). It is caused by the absence of one X chromosome in female. When an abnormal ovum without X chromosome fused with a normal sperm having X chromosome a female individual is formed having 45 chromosomes.  Turner’s syndrome symptoms:  These are sterile female incapable of reproduction with poorly developed ovaries, underdeveloped breast, small uterus, and abnormal intelligence. They have webbed neck and broad chest, cardiovascular abnormalities, and hearing impairment. They may not menstruate or ovulate.one in every 3000 female births is a victim.                                                                                   
Klinefelter’ syndrome                                                                                   
H.F.Klinefelter first described this genetic disorder. The chromosome number of the patient is 47 (44 +XXY). There is an extra chromosome in male. This syndrome originates when ovum with abnormal XX chromosomes unite with a normal sperm having Y chromosome or when normal ovum X unite with abnormal sperm carrying XY chromosomes. The individual has 44+XXY chromosomes. Klinefelter’s syndrome symptoms:  Such person is sterile male with underdeveloped testis, mental retardation, thinly scattered body hair, long limb and with some female characters such as enlarged breast (gynaecomastia) and feminine pitches voice. It arises by the non-disjunction of sex chromosomes during meiosis.