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.
Prenatal biochemical screening tests are widely used to look for chromosomal abnormalities in the fetus which can lead to serious handicap, or even death during gestation or in the first few days after birth. But these tests are only able to detect fewer than half of the total chromosomal abnormalities in the fetus, a scientist will tell the annual conference of the European Society of Human Genetics tomorrow (Monday 2 June) Dr. Francesca R. Grati, of the TOMA Laboratory, Busto Arsizio, Italy, says that these findings mean that women should be better informed on the limitations of such diagnostic tests.
An upcoming paper from Drs. Hidenori Ichijo and Hideki Nishitoh (The University of Tokyo) and colleagues lends new and valuable insight into the genetics of ALS.
Healthy men who report lower levels of the nutrient folate in their diets have higher rates of chromosomal abnormalities in their sperm, according to a new study by researchers at the University of California, Berkeley, and the Lawrence Berkeley National Laboratory.
Researchers at Johns Hopkins and Ohio State University have found that the number of copies of a particular gene can affect the severity of colon cancer in a mouse model. Publishing in the Jan. 3 issue of Nature, the research team describes how trisomy 21, or Down syndrome in humans, can repress tumor growth.
Researchers in the United States say the chromosomal abnormality that affects people with Down's syndrome also protects them against cancer.
Imagine the day when a routine visit to the family doctor includes a simple blood test to predict the risk for developing Alzheimer's disease (AD).
Researchers in the United States have discovered that an old drug once used to study epilepsy substantially improved learning and memory in mice with Down syndrome symptoms.
Researchers in the U.S. have discovered a gene mutation that shrivels brain cells which they suspect is responsible for the mental retardation seen in Down syndrome.
Researchers at Johns Hopkins restored the normal growth of specific nerve cells in the cerebellum of mouse models of Down syndrome (DS) that were stunted by this genetic condition. The cerebellum is the rear, lower part of the brain that controls signals from the muscles to coordinate balance and motor learning.
Researchers from the Institute of Psychiatry at King's College London have identified a molecule that could be targeted to treat the cognitive impairment in people with Down syndrome.
Today the University of Colorado and The Anna and John J. Sie Foundation of Denver announced The Sie Family Down Syndrome Break-Through Research Initiative. The initiative will provide $600,000 in grant funds to stimulate new scientific research on Down syndrome with the aim of enhancing cognitive ability. These are the first such grants provided to CU for a specific chromosomal condition and the first nationwide specifically for Down syndrome.
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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