This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetic Disorders, Subject name: Biochemistry
Barr body is not present in female having- (PGMEE 2012-13) 
Select and explain. 
A. 46 XX genome, B. 45 XO genome, C. 47 XXX, D. All of the above
B: 45 XO genome
Answer: B: 45 XO genome 
Explanation: In Turner syndrome (45, XO),one of the X-chromosome is missing in a female. This is the most lethal karyotype. It is only monosomy of sex chromosome in humans. There are 45 chromosomes instead of 46 in a normal individual. Phenotype Genotype Barr bodies Normal Male XY 0 (Normal) Normal Female XX 1 (Normal) Turner Syndrome X0 0 (Female with no Barr Body) Klinfelter Syndrome XXY 1 (Male with Barr Body) Super Female XXX 2 (Female with two Barr Bodies) No. of Barr bodies = no. of x chromosome - 1 Since in XO genotype there is 1 x chromosome. Therefore, no. of barr bodies is 1-1=0