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 47 million base pairs (the building blocks of DNA) and representing approximately 1.5 percent of the total DNA in cells.
In 2000, researchers working on the Human Genome Project announced that they had determined the sequence of base pairs that make up this chromosome. Chromosome 21 was the second human chromosome to be fully sequenced.
Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 21 likely contains between 300 and 400 genes.
Genes on chromosome 21 are among the estimated 20,000 to 25,000 total genes in the human genome.
A new Cincinnati Children's Hospital Medical Center study links regions of two chromosomes to susceptibility for a type of autism characterized by regression in development. Developmental regression can include the loss of previously acquired language, social skills or both.
Research led by investigators at Beth Israel Deaconess Medical Center (BIDMC) helps explain how a group of angiogenesis inhibitor molecules serve as an important defense mechanism against the development and spread of cancer, offering key insights into why cancerous tumors grow at different rates among different individuals.
National health records have shown that African-Americans are more prone to high blood pressure than Caucasians, but pinning down the roots of that difference has proven elusive. Now, researchers at the Stanford University School of Medicine have narrowed down the search for genes that contribute to this difference in disease risk.
A gene for a rare juvenile-onset form of amyotrophic lateral sclerosis (ALS, or Lou Gehrig’s disease) has been isolated in families in the United States, Belgium and Austria, the Muscular Dystrophy Association (MDA) announced today.
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