All are chromosomal trisomies except:

Ans: c Turner syndromeTurner's syndrome is due to the absence / defect of second X chromosome and not due to trisomy.All other conditions mentioned are due to trisomies.Down syndrome - trisomy 21Edward syndrome - trisomy 18 (Eighteen)Patau syndrome - trisomy 13 (Pathimunnu)Molecular pathogenesis - Turner syndromeI. Ovaries develop normally early in embryogenesis but, absent 2nd X chromosome - leads to accelerated loss of oocytes II. Ovaries become atrophic fibrous bands devoid of ova and follicles III. Nongonadal abnormalities are due to loss of some genes that reside on the X chromosome Eg, SHOX gene (short stature homeobox gene) on X p22-23. Normally it remains active in both X chromosomes. But haploinsufficiency of this gene (as in turners syndrome) gives rise to short stature.Trinucleotide repeat# Myotonic dystrophy - CTG# Huntingtons disease - CAG# Spinocerebellar ataxia type 1 - CAG# Machado joseph disease - CAG# Spinomuscular atrophy -CAG# Dentate rubral pallidoluysian atrophy - CAG# Fragile X syndrome-CGGDefective splicing of hnRNA# Beta thalassemia# Gaucher disease# Tay sachs disease# Spinomuscular atrophy