This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics of Common Disorders, Subject name: Pediatrics
XXY klinfilter which has extra- 
Select and explain. 
A. X-chromosome, B. Y chromosome, C. Both, D. None
A: X-chromosome
Answer: A: X-chromosome 
Explanation: Ans. is 'a' i.e., X-ehromosomeo The major numerical disorders of chromosomes are 3 autosomal trisomiesTrisomy 21 -- Down syndromeTrisomy 18 - Edwards syndromeTrisomy 13 - Patau syndromeo Four types of sex chromosomal aneuploidies:Turner syndrome (usually 45,X)Klinefelter syndrome (47,XXY)47,XXX47.XYYo By far the most common type of trisomy in liveborn infants is trisomy 21 (karyotype 4 7,XX, +21 or 47,XY, +21) or Down syndrome.