People with Down syndrome have 47 chromosomes.

Studies shown that chromosome 21 contains 200 to 250 genes.

Using yeast genetics and a novel scheme to selectively remove a single protein from the cell division process called meiosis, a cell biologist found that when a key molecular player known as Pds5 goes missing, chromosomes fail to segregate and pair up properly, and birth defects such as Down syndrome can result.

*Chromosome 21 likely contains 200 to 300 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.

If this protein is not produced, delayed development and behavioral problems are often reported in children with Down syndrome. Affected individuals' speech and language develop later and more slowly than in children. without Down syndrome can include attention problems, obsessive/compulsive behavior,mor tantrums. A small percentage of people with Down syndrome are also diagnosed with developmental conditions called autism spectrum disorders, which affect communication and social interaction.

This disorder type is also know as Trisomy 21.

The chromosome number of Down syndrome is 47.

Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 21, one copy inherited from each parent, form one of the pairs. Chromosome 21 is the smallest human chromosome, spanning about 48 million base pairs (the building blocks of DNA) and representing 1.5 to 2 percent of the total DNA in cells.

These results indicate that the Down syndrome phenotype of this patient is due to microduplication of a chromosome 21 fragment containing the CuZn SOD gene.