Commemorating the discovery of DNA fingerprinting

Some time ago, I did a post about fingerprinting and personal identification. Now while fingerprinting has been around for more than 150 years, a new breakthrough in personal identification happened much more recently – on this day in 1984, DNA fingerprinting was discovered in Leicester, England.

The man who discovered this revolutionary new technique, was Sir Alex Jeffreys of the University of Leicester. He was the first to realised that each person’s DNA has a unique pattern, almost like a bar code, and that this could be used as a biological identification method. The technique has, over the past 25+ years, proved an invaluable tool in forensics, crime investigations and identification of genetic relationships.

Geneticist studying a DNA profile.
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Of course no technique is perfect, and in the case of DNA fingerprinting there are also rare occasions where the technique cannot be used. Identical twins, for example, have matching DNA, and so their DNA fingerprints are the same.  A much rarer, and much stranger, occurrence is when a single person has more than one DNA fingerprint.

Strange as this may seem, having a single person with two distinct genetic identities is possible. This condition is known as chimerism, named after the chimera, a mythological creature with features from more than one distinct animal, for example a lion’s head and a serpent’s tail.

A human chimera is formed during pregnancy. Normally the male gamete (sperm) fuses with the female gamete (ova) to form a zygote, the cell that becomes the embryo. This embryo has a new genetic identity, formed from a unique combination of the DNA of the mother and the father. On rare occasions, two male gametes will fuse with two female gametes, to form two zygotes which develop into two (non-identical) twin embryos. These embryos will each have a different, unique new DNA fingerprint, inherited from the father and mother.

In extremely rare cases, these two embryos can fuse, growing into a single child, but formed from four gametes, and thus having two distinct sets of DNA. The chimera child can grow up without anyone ever knowing about his double identity, but may in fact have different organs or body parts that have completely different genetic fingerprints. Even when a DNA identity test is done on a chimera, DNA will usually only be taken from a single source, such as a blood sample or cheek swab, and the second identity may never be known.

Chimerism may, in rare occasions, visibly manifest itself, for example with people having both male and female reproductive organs, or two different colour eyes. (However, different eye colours, or heterochromia, can have different causes, and is, as far as I know, not necessarily an indication of chimerism.)

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The most famous example of a chimera confounding DNA profiling came from a case in 2003, when a mother of three were told, after DNA tests were done on her and her three children, that two of her three sons were not hers, even though she maintained that she had conceived them with her husband, and delivered them naturally.

After more extensive testing, it was discovered that she was a chimera, and that the two sons thought not to be hers did in fact match her ‘second identity’.

Definitely a case where truth is, in fact, stranger than fiction.

Celebrating the birth of the first ‘test tube’ baby

Today we celebrate a special birthday – Louise Joy Brown, the world’s first ‘test tube’ baby, was born on this day back in 1978 in Oldham, England.

Louise was conceived in a petri dish (so technically she was a ‘petri dish baby’ rather than a ‘test tube baby’), via the process of in vitro fertilisation (IVF). Her parents, Lesley and John Brown, had been trying to conceive for nine years, but faced complications of blocked fallopian tubes.

The process was a great success, and amazingly, by the time Louise turned 21 in 1999, more than 300 000 babies had been born using similar IVF techniques.

Louise’s IVF was performed by Dr Robert Edwards of Cambridge, who had previously successfully performed similar procedures with animals. He was assisted by gynaecologist Patrick Steptoe, who was already the Browns’ doctor. Edwards was awarded the 2010 Nobel Prize in Medicine for his contributions in the field of reproductive medicine.

The Latin term ‘in vitro’ is used for any biological process that occurs outside the organism it would normally be occurring in.
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In vitro fertilisation is a procedure where an egg cell gets fertilised by sperm outside the body. After successful fertilisation, the fertilised egg (zygote) gets transferred to the patient’s uterus in order to continue developing like a normal pregnancy.

The term in vitro (Latin: ‘in glass’) came about to describe a procedure that specifically occurred in a glass container (such as a test tube or petri dish), but its use has been extended to refer to any biological procedure that occurs outside the organism it would normally be occurring in.

Louise Brown got married in 2004, and her own son, conceived naturally, was born in late 2006. Happy 34th birthday, Louise!