Do people with down syndrome have an X chromosome?

Yes, individuals with Down syndrome have an X chromosome, just like everyone else. Down syndrome is typically caused by the presence of an extra copy of chromosome 21, resulting in three copies instead of the usual two. This condition is not directly related to the X chromosome, which is one of the sex chromosomes involved in determining biological sex. Both males and females with Down syndrome have one X chromosome and one Y chromosome (for males) or two X chromosomes (for females).