Final answer:
Trisomy 21, or Down syndrome, is a genetic disorder characterized by an extra chromosome 21, leading to developmental delays and physical features such as a flat facial profile and upward slant to the eyes. It's more likely to occur in children born to older mothers and individuals with Down syndrome are generally more likely to live into adulthood compared to other aneuploidies like trisomy 18.
Step-by-step explanation:
Features of Trisomy 21
Trisomy 21, commonly known as Down syndrome, is a genetic condition characterized by an extra copy of chromosome 21. This extra genetic material results in a range of physical and mental features unique to the condition. Key features of Down syndrome include distinct facial features such as a flat facial profile, upward slant to the eyes, and a single deep crease across the center of the palm. Additionally, individuals with Down syndrome often have developmental delays, varying degrees of intellectual disability, and are at increased risk for certain medical conditions like congenital heart defects, respiratory and hearing problems, and thyroid conditions. It is not typically associated with the development of chronic diabetes or ankylosing spondylitis, which are not considered characteristics of trisomy 21.
The likelihood of having a fetus with trisomy 21 increases significantly with maternal age, based on findings that the incidence of this condition is higher in births to older mothers. This highlights the importance of age as a risk factor for Down syndrome.
Compared to other aneuploidies such as trisomy 18, individuals with Down syndrome are more likely to survive to adulthood. This suggests that the genetic material on chromosome 21 is less detrimental in excess compared to that on chromosome 18, which typically causes more severe and often lethal conditions such as Edwards syndrome.