GENETICS AND GENEALOGY

From a Lecture to the Society of Genealogists

by Dr Geoff Swinfield.

 

Dr Swinfield set the background to his talk by speaking of scientists carrying out research into genetically inherited characteristics of humans and animals in the hope of being able to cure their diseases. He discussed how the genes could affect the health or appearance of a person and how the information is passed on through reproduction. He described genetic material as a conduit for succession with the warning that it can change or mutate. Would it be possible to map these changes? Geoff then posed the question whether or not these studies or tests could be used to back up what you have found out about your family tree through genealogical research. He argued that the latter could be misleading and not be true genetically if, for example, illicit relationships had taken place!

 

The genetic code is based on four chemicals described by the letters A, C, T, G and the changes brought about by mutation. The most important difference in any group of people is their sex without which no variation in characteristics can be carried forward to future generations. Geoff had a bit of fun with us by asking how many could roll our tongues. A lot of the genetic chain he described as junk, likening it to the packing material in a parcel where an important item is surrounded by the protective packaging. Mutations here have no damaging effects on the carrier.

 

The inherited information for tongue rolling, blood group, hair and eye colouring are attributable to dominant and, recessive genes. These factors were found, about 50 years ago, to be carried on chromosomes of which each of us has 46 in 23 pairs. 44 of these are called autosomes and the final two are the sex  chromosomes, X or Y. XX represents a female and XY the male. The Y chromosome is passed from father to son. It is small and only has three major genes. Somehow these cause the voice to break, the production of body hair and, of course, sperm. The passage of the Y chromosome is linked to the passing of the surname from one generation to the next in males.

 

There are two ways in which we can test for ancestry. One is by using the Y chromosome and the second is through the Mitochondrial DNA. The latter is not part of the 46 chromosomes but a separate piece of genetic material that is found in almost all cells as it generates energy. This material it is too large to be carried by sperm and hence it can only be transmitted through the female line. Grandmother to mother and then to the daughter. It is given to sons but they cannot, in turn, pass it on.

 

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