What is the cause of Down Syndrome during meiosis?

Down Syndrome is a genetic disorder caused by the presence of an extra copy of chromosome 21. This can occur during meiosis, the process by which sex cells (eggs and sperm) are formed.

During meiosis, the chromosomes in a cell are duplicated and then separated into two new cells. In most cases, each new cell receives one copy of each chromosome. However, in some cases, an error can occur during meiosis called nondisjunction. This is when both copies of a chromosome end up in the same new cell.

If this happens with chromosome 21, the resulting egg or sperm will have an extra copy of this chromosome. When an egg with an extra copy of chromosome 21 is fertilized by a sperm with a normal number of chromosomes, the resulting embryo will have Down Syndrome.

Down Syndrome can also be caused by a translocation. This is when a piece of one chromosome breaks off and attaches to another chromosome. If this happens with chromosome 21, it can result in an extra copy of this chromosome in some cells of the body. This can lead to Down Syndrome.

Down Syndrome is the most common genetic cause of intellectual disability. It affects about 1 in 700 babies born in the United States.