Extra copy of 21st chromosome causes _________ in human.

Step-by-step solution

Down's syndrome is a genetic disorder caused by the presence of an additional copy of chromosome 21 , also known as Trisomy 21 . Turner's syndrome is caused by the absence of one of the X chromosomes, resulting in a 45 , X 0 karyotype. Klinefelter's syndrome is caused by the presence of an additional X chromosome, resulting in a 47 , XXY karyotype. Thalassemia is an autosomal recessive blood disorder. Therefore, an extra copy of the 21 st chromosome causes Down's syndrome. Answer: Down's syndrome