What do you think is the reason why an extra copy of chromosome 1, 2, 3, 4 or 5 results in more severe abnormalities than an extra copy of chromosome 21?

Chromosomal mosaicism occurs from an error in cell division in cells other than eggs and sperm. Most commonly, some cells end up with one extra or missing chromosome (for a total of 45 or 47 chromosomes per cell), while other cells have the usual 46 chromosomes.

Explanation:

Why does an extra copy of one chromosome?

Chromosomal mosaicism occurs from an error in cell division in cells other than eggs and sperm. Most commonly, some cells end up with one extra or missing chromosome (for a total of 45 or 47 chromosomes per cell), while other cells have the usual 46 chromosomes.

About 95 percent of the time, Down syndrome is caused by trisomy 21 — the person has three copies of chromosome 21, instead of the usual two copies, in all cells. This is caused by abnormal cell division during the development of the sperm cell or the egg cell.

The Lend-Lease Act stated that the U.S. government could lend or lease (rather than sell) war supplies to any nation deemed “vital to the defense of the United States.” Under this policy, the United States was able to supply military aid to its foreign allies during World War II while still remaining officially neutral in the conflict. Most importantly, passage of the Lend-Lease Act enabled a struggling Great Britain to continue fighting against Germany virtually on its own until the United States entered World War II late in 1941.