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.
The genomic analysis technologies enable the study of genetic factors related to numerous diseases. In few areas this researches brought such a big and useful volume of information as in the case of melanoma.
Researchers at Universitat Aut-noma de Barcelona, in collaboration with the Vall d'Hebron Hospital Fetal Tissue Bank, the Department of Gynaecology and the Research Unit of Paediatric Endocrinology, analysed the effects of Bisphenol A (BPA), a polymer widely used to manufacture plastics, in an in vitro culture of ovaries.
Cancer patients may view their tumors as parasites taking over their bodies, but this is more than a metaphor for Peter Duesberg, a molecular and cell biology professor at the University of California, Berkeley.
Sequenom, Inc., a life sciences company providing innovative genetic analysis solutions, today announced it has signed a three-year supply agreement with Illumina, Inc., a leading developer and manufacturer of life sciences tools for the large-scale analysis of genetic variation and function.
A strategy that has been shown to reduce age-related health problems in several animal studies may also combat a major cause of age-associated infertility and birth defects.
At present, when a woman undergoes preimplantation genetic screening (PGS) in a fertility clinic, doctors are trying to select an egg or an embryo that is healthy and doesn't have a chromosome abnormality such as an extra copy of chromosome 21, which causes Down's syndrome. In order to establish this, they either have to biopsy a part of the egg called the polar body or remove a cell from the embryo for screening. Both procedures are expensive, invasive and can damage the egg or embryo.
Ovarian stimulation undertaken by women of advanced maternal age receiving fertility treatment may be disrupting the normal pattern of meiosis - a critical process of chromosome duplication followed by two specialised cell divisions in the production of oocytes and sperm - and leading to abnormalities of chromosome copy numbers that result in IVF failure, pregnancy loss or, more rarely, the birth of affected children with conditions such as Down's syndrome, which is caused by the inheritance of three copies of chromosome 21.
A protein associated with Alzheimer's disease clogs several motors of the cell transport machinery critical for normal cell division, leading to defective neurons that may contribute to the memory-robbing disease, University of South Florida researchers report.
Dana-Farber Cancer Institute scientists have discovered new details of how cancer cells escape from tumor suppression mechanisms that normally prevent these damaged cells from multiplying. They also demonstrated a potential link between this cell proliferation control mechanism and the cognitive deficits caused by Down syndrome.
Researchers have zoomed in on mouse chromosomes to map hotspots of genetic recombination - sites where DNA breaks and reforms to shuffle genes. The findings of the scientists at the National Institutes of Health and Uniformed Services University of Health Sciences (USU) have the potential to improve the detection of genes linked to disease and to help understand the root causes of genetic abnormalities.
Scientists at the European Molecular Biology Laboratory in Heidelberg, Germany, have developed a new method for studying gene regulation, by employing a jumping gene as an informant. Published online today in Nature Genetics, the new method is called GROMIT.
Gene therapy that boosts the ability of brain cells to gobble up toxic proteins prevents development of Alzheimer's disease in mice that are predestined to develop it, report researchers at Georgetown University Medical Center. They say the treatment - which is given just once - could potentially do the same in people at the beginning stages of the disease.
In a study published online today in the American Journal of Obstetrics & Gynecology, researchers from the Sequenom Center for Molecular Medicine confirmed that DNA sequencing of maternal blood plasma could accurately detect trisomy 21.
According to experts a simple DNA test for Down syndrome could save nearly all pregnant women from invasive tests like amniocentesis. Usually 3% to 5% of pregnant women in the UK or some 30,000 women have to undergo invasive tests like amniocentesis that increases the risk of miscarriage to 1%. The new DNA blood test could bring this down to 0.1%, according to a study in the British Medical Journal.
Sequenom, Inc. today announced that the company's wholly-owned reference laboratory, the Sequenom Center for Molecular Medicine (Sequenom CMM), has authorized commencement of a pivotal clinical validation study. This validation study is designed to evaluate the clinical performance of the SensiGene T21 Laboratory Developed Test (LDT) for the detection of an overabundance in maternal blood of chromosome 21, which is associated with fetal chromosome 21 aneuploidy.
Scientists have discovered an amazingly simple way that cells stabilize their machinery for forcing apart chromosomes. Their findings are reported Nov. 25 in Nature.
Neuroscientists in the Down Syndrome Research Group at the University of Arizona have created a battery of tests that quickly aid in the assessment of the cognitive abilities of persons with Down syndrome.
Down syndrome is a well known cause of mental retardation and other medical problems, including early onset of Alzheimer disease. It has long been known that Down syndrome is associated with an individual having an additional copy of chromosome 21. Research findings reported in the July 18 advanced online publication of Nature Neuroscience have narrowed down the critical genetic elements responsible for some aspects of Down syndrome.
Researchers in The Netherlands believe they are on the verge of developing a simple, prenatal blood test that would be able to detect accurately chromosomal abnormalities in the developing foetus.
Researchers in The Netherlands believe they are on the verge of developing a simple, prenatal blood test that would be able to detect accurately chromosomal abnormalities in the developing foetus. At present, the only reliable way to do this is through amniocentesis or chorionic villus sampling, both of which are invasive and carry the risk of triggering a miscarriage.
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