Final answer:
Malformation of chromosome 21, known as trisomy 21, is responsible for Down syndrome. This genetic condition involves an extra chromosome 21 and can lead to intellectual and physical impairments. Down syndrome is commonly caused by nondisjunction during meiosis, and risk increases with maternal age.
Step-by-step explanation:
Malformation of chromosome 21 is responsible for down syndrome. This condition arises due to an extra copy of chromosome 21 in the individual's cells, a situation referred to as trisomy 21. A common cause of this chromosomal abnormality is nondisjunction during meiosis, which is the process of cell division that produces reproductive cells (sperm and eggs). Typically, individuals with Down syndrome have a total of 47 chromosomes in their cells instead of the usual 46. They can exhibit intellectual disability, congenital heart disease, visual problems, a distinct facial appearance, and are also more susceptible to certain types of cancer.
The risk of conceiving a child with Down syndrome increases with the mother's age, particularly for mothers over 36. The condition can be detected in utero using karyotype analysis where the presence of an extra chromosome 21 can be visually confirmed. While the parents may not have Down syndrome themselves, nondisjunction during the formation of reproductive cells can lead to their child having Down syndrome.