Final answer:
The most common chromosomal disorder is Down syndrome, also known as trisomy 21, which results from an extra copy of chromosome 21 due to nondisjunction during meiosis. It manifests with mental and physical challenges and is more common with increasing maternal age.
Step-by-step explanation:
Most Common Chromosomal Disorder
The most common chromosomal disorder is Down syndrome, which is scientifically referred to as trisomy 21. This condition arises when an individual has three copies of chromosome 21 instead of the usual two, leading to a total of 47 chromosomes. Down syndrome is characterized by mental and physical impairments, and specific facial features, and is the only autosomal trisomy where affected individuals frequently survive into adulthood. The primary cause of Down syndrome is nondisjunction during meiosis, an error in cell division where chromosomes fail to separate properly. The likelihood of having a child with Down syndrome increases with maternal age, particularly in females over 36, largely because eggs have a higher risk of nondisjunction compared to sperm.
Other chromosomal disorders include Klinefelter syndrome in males, where there is an extra X chromosome, resulting in an XXY genotype and physical and learning challenges. Chromosomal disorders can also involve the loss of chromosome parts, such as in Cri du chat syndrome, where part of chromosome 5 is missing. Nevertheless, abnormalities in chromosome number are often the most identifiable, as they can be observed in a karyogram.