Calico cats may hold the secret to losing weight. Really. The orange, black and white felines may be called "money cats," but soon, they may one day be known as "weight loss cats." 

The secret may lie in the unusual structure of their chromosomes. These are strands of DNA and protein that code for genetic traits like hair and eye color. Females inherit one X chromosome from each parent, while males are formed with one X from their mother, and one Y from their father. Just prior to cell division, these genes look a little like the letters after which they are named. 

Calicos have a gene that codes for orange fur on one of their X chromosomes and another that calls for black fur on the other X chromosome. One of these genes is silenced in each cell of the cat's body, leading to the unusual colors. This is also why calicos are nearly always female. 

Since the 1960's, it has been known that chromosomes can be turned on and off. Biologists also knew the patterns of these animals were carried on these structures. The latest research into the way genes are turned on or shut off in calico cats was carried out by Elizabeth Smith, a postdoctoral fellow in the anatomy department of University of California, San Francisco. The team wants to determine how these genes are controlled without altering the DNA within the gene. 

"Uncovering how only one X chromosome is inactivated will help explain the whole process of epigenetic control, meaning the way changes in gene activity can be inherited without changing the DNA code. It can help answer other questions such as if and how traits like obesity can be passed down through generations," Smith said in a press release.

Many genetic disorders are carried on the X chromosome, and some of these can be inherited by children. Smith and her researchers believe obesity may be one of the predispositions to be carried on the gene. The distribution of body fat has been previously shown to be controlled by these chromosomes. By studying the way these genes are shut off in calico cat, the team believes they may be able to "switch off' undesirable genetic instructions, including those that lead to obesity. 

Researchers were able to view the chromosomes using a new method called soft x-ray tomography. This system uses fluorescence to delivery 3D views of structures within cells. 

"With new fluorescent probes, we can start identifying the position of specific genes in context - inside the tangled network of DNA within the intact nucleus," Smith wrote.

DNA has been studied by researchers for well over five decades. This is the first time, however, that the carrier of genetic information has been imaged within the intact nucleus of an unfixed, hydrated, complete cell. 

Details of the study were presented at the 58th Annual Biophysical Meeting in San Francisco on 18 February.