Teen prefers Genes to Jeans

by HOMEDNA on 10/05/2010

The Wall Street Journal ran a very interesting story about Anne West, a 17-year old girl who is making a big splash in the world of science.  Her friends call her a ‘bio nut’ because she likes biology so much.  She hasn’t had time to study for her driver’s license test yet, but Anne is making time to study her family’s genome.  She is analyzing their DNA using her home computer, looking for trends and kernels of important information within billions of data points.

DNA really is amazing. Paternity testing makes use of less than 1% of the data available from a full sequencing of a family’s genome.  In fact, scientists often use the term ‘junk DNA’ to refer to the parts of the DNA used for identity and relationship testing.  Paternity testing has become routine, fast, and so much a part of our culture that it is a staple of television dramas and talk shows.  It’s great that budding scientists like Anne get excited about discovering the next frontier in biology.

DNA Relationship Testing for 5,300 Year-old Iceman

by HOMEDNA on 08/09/2010

 

In 2010, scientists  completed sequencing the genome for Otzi the Iceman, whose 5,300-year-old  mummy was discovered in the Otztal Alps

Past discoveries, such as his goat hide clothes, the food that he ate shortly before his death (unleavened bread and meat) and even the arrow wound in his shoulder all provided clues and insights into the life of our ancestors more than 5,000 years ago.

The  genome sequencing, which was completed by scientists at Institute of Human Genetics at the University of Tuebingen, could provide us with even more information on the Iceman, such as the color of his eyes or hair, even diseases he may have suffered, or what his immune system was like.

The most exciting answer that may be provided by this research is, does he have any living relatives?

Relationship Testing

The mapping of the DNA within the nuclei of the Iceman’s cells, along with the genetic information collected from  a large number of people living in the region (and the most likely people to be descendants of the iceman)  may help finally answer the question:

“Are there any living relatives of the Iceman still around?”

Scientists have previous attempted to find living relatives of the Iceman. Using an analysis of the Iceman’s mitochondriaI DNA, comparisons were done against the data of groups of living individuals. Mitochondrial DNA is passed down from mothers to their children and so would only provide relatives on Iceman’s mom’s side of the family. No matches where found, indicating that his maternal lineage is either very rare or died out.

Can my DNA Paternity Test be wrong because I’m a Chimera?

by HOMEDNA on 08/02/2010

Human chimeras are a popular topic for TV shows and crime scene dramas. This extremely rare and interesting genetic condition can lead to the question,“Can my DNA Paternity Test be wrong because I’m a chimera?”

Named for the mythical monster with a lion’s head, a goat’s body and the tail of a snake, human chimeras have two or more genetically distinct types of cells in their bodies. This anomaly is thought to be caused by the absorption, or fusing, of twins before they are born. This would cause the chimera to carry two sets of DNA in their body. One set of their DNA and one that would have been their twin’s DNA. This second set of DNA can show up anywhere in the body. A second, distinct set of DNA may be present in the skin, blood, or even reproductive organs of the chimera. This was what happened in the case of Lynda Fairchild, profiled in the ABC documentary.

She’s her own Twin

Fairchild underwent DNA maternity testing shortly after the birth of her child. Results showed a poor match, as if she was the baby’s grandmother. It was concluded that Fairchild may have been a chimera, her body the result of the fusion of two non identical embryos at the earliest stage of development. Different parts of her body could have come from different cell lines. Further testing indicated that cells taken from her reproductive organs, contained different DNA than those taken from her mouth for the DNA testing and were a match to her children.

Though cases like this are often given a lot of press, their occurrence is very rare. No one knows exactly how many cases of human chimera there are, but most studies cite only 30 reported cases in all of human history.

What does this mean for DNA paternity testing?

An inclusion, or “positive” DNA paternity test shows that an alleged father and the child share the same DNA. Therefore that man is considered to be the biological father. The father’s DNA was passed to the child, and the loci (markers) all match up. It’s virtually impossible (that is, very, very unlikely) that possessing two sets of DNA would make someone appear to be a father when they are not.  Matches at all locations indicate a positive paternity test result, even if the father is a chimera.

An exclusion (when a man is not the father of a child) could potentially be affected, by someone being a chimera. It is possible for a chimera to pass one set of DNA on to their child but show a second set of DNA with a cheek swab, as in the Linda Fairchild case.  Even so, the child and the father would still likely show a partial match, similar to that of a child and an uncle, since the second set of DNA would be that of the father’s unborn twin.

Disputed Maternity Leads to Identification of Tetragametic Chimerism – The New England Journal of Medicine

Genetic Mosaics

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