Final answer:
Trisomy 21, or Down syndrome, is a genetic condition characterized by an extra copy of chromosome 21, typically caused by chromosomal nondisjunction during meiosis, especially in pregnancies of older women. Karyotype analysis can reveal this extra chromosome and help diagnose the condition, which comes with intellectual and physical challenges.
Step-by-step explanation:
The student's question Trisomy ___, or Down syndrome, has been the focus of intense study refers to Trisomy 21. Down syndrome is caused by the presence of an extra copy of chromosome 21, which leads to physical and mental impairments, as well as characteristic facial features. This condition occurs due to chromosomal nondisjunction during meiosis, which becomes more likely as maternal age increases, particularly in females over the age of 36. Aneuploidy such as trisomy occurs when there is an error in chromosome number during cell division, leading to an individual having three of a particular chromosome instead of the usual two. A karyotype analysis, which is a picture of the cell's chromosomes, can identify this extra chromosome. The additional genetic material from the extra chromosome contributes to the various symptoms associated with Down syndrome, which include intellectual disability and an increased risk for certain health issues.