The number of sex chromosomes is normal for Down’s syndrome. Down syndrome is a genetic disorder and caused due to abnormal cell division that results in an extra copy of chromosome 21 (trisomy 21). A normal human contains 46 chromosomes (44 autosomes and two sex chromosomes (XX or XY)). However, in the case of Down’s syndrome (Trisomy 21) (44+XY+21) for males and (44+XX+21) for females. As the genetic disorder does not affect the number of sex chromosomes, a person with Down’s syndrome posses normal numbers of sex chromosomes.
Some common physical features of Down syndrome include A short neck with a flattened face, small ears, tongue stick out of the mouth, small hands and feet, loose joints with poor muscle tone (hypotonia), shorter in height, presence of single crease across the palms on the hands, etc.
A person with Down’s syndrome also has a greater risk for other medical problems such as congenital heart disease, musculoskeletal and movement problems, hearing loss, speech apraxia, sleep disorder, learning disabilities, and intellectual disabilities.