Final answer:
Down syndrome, or Trisomy 21, is a genetic disorder caused by an extra copy of chromosome 21 due to chromosomal nondisjunction during meiosis, commonly associated with maternal age over 36. Aneuploidy refers to deviations from the normal chromosome number, leading to significant health and developmental challenges.
Step-by-step explanation:
Chromosomal disorders are conditions caused by alterations in the number or structure of chromosomes. One of the most well-known disorders is Down syndrome, also referred to as Trisomy 21, where an individual has three copies of chromosome 21 instead of the usual two. This results from a chromosomal nondisjunction during meiosis, and its occurrence is more frequent in children born to women over 36. Down syndrome is characterized by certain physical features, cognitive impairments, and developmental delays. However, this is not the only chromosomal abnormality; conditions like cri du chat syndrome, where a segment of chromosome 5 is missing, also lead to significant physical and developmental challenges.
A situation in which there is a deviation from the normal number of chromosomes is termed aneuploidy. Human zygotes that are monosomic (missing one autosome) do not typically survive to birth. In contrast, some trisomy. specifically those involving smaller chromosomes like chromosomes 13, 15, 18, 21, and 22, may result in live births, though these individuals often face severe health issues and developmental problems. It is important to understand both the genetic and environmental factors, such as parental age, that contribute to the likelihood of these disorders.