Which of the following is NOT a characteristic of Down Syndrome?

The reasoning behind the answer lies in the genetic basis of Down syndrome. Individuals with Down syndrome typically have a total of 47 chromosomes due to the presence of an extra copy of chromosome 21, which is known as trisomy 21. This genetic variation is a hallmark characteristic of the disorder.

While individuals with Down syndrome often experience deficits in social skills, this is not an indicator of the chromosomal abnormalities associated with the condition. Instead, these social skill deficits are related to the overall cognitive and developmental challenges that can arise from the extra genetic material.

The option regarding a missing chromosome 18 does not apply to Down syndrome, making it the correct distinction to highlight. Down syndrome does not involve the absence of chromosome 18; rather, it specifically involves an extra chromosome 21. Thus, the presence of 47 chromosomes and the additional copy of chromosome 21 are fundamental characteristics of Down syndrome, while the missing chromosome 18 does not align with the recognized genetic profile of the condition.