A) 21st trisomy
B) two X and one Y chromosomes
C) 19 trisomy
D) only one X chromosome
Correct Answer: A
Solution :
Downs syndrome is characterized by 21st trisomy which is common in children and is characterized by mental retardation, a short body, swollen tongues and eyelid folds resembling those of mongolian races. Klinefelters syndrome is characterised by two X and one Y chromosomes. It is produced by fusion of normal androsperm (22+Y)with egg having 2X (22+XX) or normal egg (22+X) with sperm having both chromosomes (22+XY). The individuals are males with undeveloped tesres, azospermia, occurence of barr body, feminine secondary sex characters (gynecomastia) like very few body hair and enlarged breasts. Turners syndrome is characterised by only one X chromosome. There is single X-chromosome (44+XO) due to fusion of (22+0) ovum with gynosperm (22+X). The individuals are female with limited secondary sex characters, rudimentary ovaries, lack of menstrual cycle, sparse pubic hair, undeveloped breasts, subnormal intelligence etc.
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