Carbon copies and DNA

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The Human Genome Project completed mapping the DNA sequence that contains all the information needed to build a human body in 2003.  Since then, DNA testing has come within the reach of family historians, requiring just a sample of body cells.

The DNA molecule is made up of two strands of complimentary base pairs that fit together like a zip. DNA is replicated by unzipping its two strands and making a new partner strand for each original strand, producing an indentical copy.  The instructions contained in the sequence of base pairs are copied much like carbon paper can replicate a list of names.  Mutations happened when the copying process is not perfect.

DNA is not kept as a simple string within our cells.  It is packaged up into chromosomes and each package keeps a selection of instructions together, a bit like binding the pages of a book.

When ordinary body cells divide to produce 2 new cells, two sets of complete chromosomes are copied to each cell, a process called mitosis. The book analogy is that each cell gets a complete book with identical pages.

Making a new person is a little more complicated than growing and dividing ordinary cells.  When egg and sperm cells are created, through a process called meiosis, only half of the DNA goes to each cell. The process is complicated further, with mixing of parts of the DNA.  Each human embryo, made by combining an egg and sperm, gets half of it’s DNA from each parent, in a unique mix.  Using the book analogy again pages are swapped between books.

Understanding these processes is critical to interpreting DNA test results.  Dr Maurice Gleeson will explain how DNA test results can assist family history research at the Suffolk Family History Fair on 24 September.  See you there?

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