Question

Down syndrome is normally caused by?

1) an extra chromosome in the person's genetic makeup.
2) a missing chromosome in the person's genetic makeup.
3) malnutrition during the first few months of life.
4) prenatal exposure to an addictive drug.

Answer 1

Down syndrome is caused by an extra copy of chromosome 21, known as trisomy 21, resulting from chromosomal nondisjunction during meiosis.

Step-by-step explanation:

Down syndrome is normally caused by an extra chromosome in the person's genetic makeup. Specifically, it is the presence of three copies of chromosome 21, instead of the usual two, which is referred to as a trisomy 21 condition. The most common cause for this extra chromosome is a process called chromosomal nondisjunction during meiosis, which is the cell division process that creates sperm and egg cells. Nondisjunction happens when homologous chromosomes do not separate properly. The likelihood of this incidence increases with maternal age, particularly in women over 36 years old.

Down syndrome is characterized by a range of developmental and physical features, and individuals with this condition may have cognitive impairment, characteristic facial appearances, and an increased risk of certain medical conditions.

Answer 2

Down syndrome is caused by trisomy 21, which is the presence of an extra third chromosome 21 due to chromosomal nondisjunction during meiosis. So, the correct option is 1) an extra chromosome in the person's genetic makeup.

Step-by-step explanation:

Causes of Down Syndrome

Down syndrome is primarily caused by an extra chromosome in a person’s genetic makeup. Specifically, it is characterized by having three copies of chromosome 21 instead of the typical two, a condition known as trisomy 21. The most common mechanism leading to this extra chromosome is chromosomal nondisjunction during the process of meiosis, which is when the reproductive cells, such as eggs and sperm, are formed. Nondisjunction events, where chromosomes fail to separate properly, increase with maternal age, especially in women over 36 years of age. Consequently, there is a higher chance for a child to be born with Down syndrome as the age of the mother increases.

The presence of an extra chromosome results in 47 chromosomes in total instead of the typical 46. This chromosomal abnormality leads to a series of developmental and physical traits associated with Down syndrome, such as cognitive impairment and distinctive facial features. Although Down syndrome is a genetic condition, it is crucial to understand that it is not inherited in the way that genes for hair or eye color are; rather, it occurs due to an error during cell division. In summary, the correct option in response to the question about what normally causes Down syndrome is option 1: an extra chromosome in the person's genetic makeup.