A chromosome is a long molecule of DNA that carries genetic material which was discovered in the late 1800s. The shape of the chromosome also determines the gender of the child, chromosome shaped XX is used for females and XY for males. The reason for chromosomes having an X shape was unknown until recently, scientists led by Professor Daniel Panne, of the University of Leicester, and Dr Benjamin Rowland, of the Netherlands Cancer Institute, now believe the answer may lie in a protein called shugoshin (also known as SGO1), which helps “lock” the chromosomes into X-shapes.
Chromosomes get their X shape during cell division. When a cell divides into two to make new cells, chromosomes copy the DNA and divide it into the two new cells. DNA in each cell is about two meters long, so cells use a process to turn DNA into compact parcels to make it fit. As part of the process, the cells leave the two copies attached in the middle until they divide. Before cell division, the X is released at the center and each arm of the X goes to one of the two cells. In case of any one of the cells getting less or more DNA, it can lead to cancer or to genetic conditions, like Down Syndrome.
Dr Rowland said, “A chromosome actually consists of two identical long DNA threads that at first are connected along their entire length. A host of ring-shaped cohesin (complex protein) molecules holds the two threads together. When a cell is about to divide, the cohesin rings open and the arms of the DNA come apart.”
The researchers discovered that the protein, SGO1, uses a 'molecular key' that fits into a 'keyhole' in cohesin, locking the cohesin rings and giving chromosomes their X shape. Which allows us to conclude that the X acts as a ‘scissor’ to cut the DNA and divide. Dr. Prof Panne claims it was exciting to understand at a molecular and atomic level how the iconic X-shape of chromosomes is generated during cell division. With new discoveries that are revolutionizing the very way of living for many humans, this breakthrough forces us to realize that some of the smaller mysteries of science can also leave us perplexed.
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