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Chromosome 21
May 08, 2000

The race to detail the human genetic code moved closer to the finish line today. A consortium of genetic research teams in Germany and Japan announced that the mapping of Chromosome 21—responsible for Down Syndrome, Alzheimer’s, and Lou Gehrig’s disease—is complete.

Why is Chromosome 21 important?

Aside from Down Syndrome,Alzheimer’s and Lou Gehrig’s disease (amyotrophic lateral sclerosis), Chromosome 21 is also responsible for breast and lung cancers and leukemia.

The mapping of Chromosome 21 is part of the much larger Human Genome Project, in which teams of researchers across the globe are racing to determine the workings of the human genome. By learning how the millions of bits of DNA make up a person’s genetic template, scientists hope to learn how to prevent these and other diseases linked to specific genes.

Researchers work with representations of DNA sequences.
This latest achievement was made by a consortium of genetic research teams including Germany’s Max Planck Institut, the RIKEN Genomics Science Center in Japan. Researchers at Denver’s Eleanor Roosevelt Institute (ERI) collaborated in the project.

In sequencing the chromosome, the researchers were surprised to find that of the 33.5 million bits of genetic material, only 3 percent of it is functional. An important discovery, since scientists can now focus their research on the working genes. It also means there may turn out to be fewer working genes overall in humans than previously thought.

What’s next?

ERI joined the consortium after investigating Down Syndrome and its effects on "learning strengths and weaknesses that people with Down Syndrome have," says David Patterson, president of ERI. Also known as Trisomy 21, Down Syndrome results when children are born with an extra copy of Chromosome 21. The condition occurs in approximately one out of every 800 to 1000 infants.

An ERI researcher points to the map of Chromosome 21 where an altered gene can cause Alzheimer’s.
Patterson says the Institute aims to "identify which genes on this chromosome are important for learning and to determine why it is that having extra copies of those genes makes certain learning tasks difficult." The ultimate goal is to one day to correct the defective genes.

Still, the gene sequencing may be "the easy part" of the effort to detect and treat genetic defects, says ERI senior scientist Kathleen Gardiner. Only about one-fourth of the complement of human chromosomes have been mapped, and Patterson says that analyzing all this data will take 20 to 50 years.

But the researchers are undaunted by the magnitude of the task. "This is the beginning of true understanding of how our bodies work," says Patterson, "and how we can use that information for curing disease."

Chromosome facts

  • Each human person normally has 23 pairs of chromosomes, 46 total
  • Chromosomes are visible during cell division, or meiosis
  • Chromosome 1 in humans measures only 10 mm, yet it contains 7 cm (that’s 7000 times its length) of DNA coiled inside
  • A human’s complete DNA complement measures 5 feet long and 50 trillionths of an inch wide
  • Each chromosome is made up of genes, which in turn are made up of DNA strands wrapped around special protein frames called histones
  • Each parent contributes half of a child’s chromosome complement at conception
  • Each person has a unique genetic makeup, with the exception of identical twins and/or triplets
  • Each chromosome controls different traits, such as sex or height
  • The traits passed from parent to child are said to be heritable; for instance, hair and eye color are heritable traits
  • Drosophila, or fruit flies, have only four chromosomes, which makes them ideal for genetic research.

produced by Debra Utacia Krol

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