Final answer:
The most common chromosomal abnormality leading to birth defects is Down syndrome or Trisomy 21, characterized by an extra copy of chromosome 21 due to chromosomal nondisjunction during meiosis. Increased maternal age heightens the risk of this condition.
Step-by-step explanation:
Common Chromosomal Abnormality in Birth Defects
The most common chromosomal abnormality resulting in birth defects is Down syndrome, also referred to as Trisomy 21. This genetic disorder is characterized by the presence of an extra copy of chromosome 21. It is most frequently caused by chromosomal nondisjunction during meiosis, which is when homologous chromosomes fail to separate properly, resulting in a gamete with an abnormal number of chromosomes.
Down syndrome is associated with mental and physical impairments, and individuals with this condition often have a distinctive facial appearance. The likelihood of having a child with Down syndrome increases with maternal age, particularly in women over the age of 36, as the frequency of nondisjunction events is higher in older eggs compared to sperm.
Chromosomal disorders can have a profound impact on development, and Down syndrome is one of the few trisomies that can result in a viable birth; however, it often results in miscarriages during the first trimester when not involving live births. With proper assistance and care, individuals with Down syndrome can lead fulfilling lives.