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Q. In human beings, $45$ chromosomes/single $X/XO$ abnormality causes

Delhi UMET/DPMTDelhi UMET/DPMT 2008

Solution:

Turners syndrome: There is single $X$ chromosome $(44 + XO)$ due to fusion of $(22 + 0)$ ovum with gynosperm $(22 + X)$. Incidence rate is one in $3000$ female births. The defect is also called female Turners syndrome. Male syndrome does not survive $(44 + Y)$. The individuals are female with limited secondary sex characters, rudimentary ovaries, lack of menstrual cycle, sparse pubic hair, undeveloped breasts, short ste etc. Downs syndrome is due to trisomy of 21st chromosome $(47)$. The syndrome is characterized by rounded face, broad fore head small ears, etc. Klinefelters syndrome: Sex complement is $XXY$. Incidence rate is one in $850$ births. 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 sex chromosomes $(22 + XY)$. Edwards syndrome: Trisomy of 18th chromosome. Malformed ears, receding chin and defective nervous system.