Which of the following traits is not visible in a person with Down syndrome?

People with Down syndrome typically have low muscle tone, not high muscle tone. Low muscle tone means muscles are looser and less firm than usual. This condition is called hypotonia and affects movement and posture.

Down syndrome is caused by an extra copy of chromosome 21. This genetic difference leads to various physical characteristics. Common visible features include shorter height, shorter neck, and distinctive eye shape.

The low muscle tone in Down syndrome can make it harder for babies to learn movements. Physical therapy often helps improve strength and coordination. Other visible traits like small stature and facial features are commonly observed.