Every Man is a Book

History written in our genes

For most of our genome we receive a half of our genes from our father and a half from our mother. Each half represents shuffled combination of DNA passed down to us from our ancestors. This recombination process makes it difficult to study lines of descent - it creates a genetic mix of everyone who has come before. Fortunately for anthropological geneticists there are parts of the genome that are passed down unshuffled from parent to child


By MARIJA MITROVIĆ
from Belgrade, SERBIA


Where do we really come from? How did we get to where we live today? Why do we appear in such a wide array of different colours and features? Believe it or not, we are carrying the answers to this questions. Every man is a history book. Today we believe that first man walked on Earth 60,000 years ago. Though eons have passed, the full story remains clearly written in our genes - if only we can read it.

Since the beginning of human history, people have been wondered how traits are inherited from one generation to the next. Although children often look more like one parent than the other, most offspring seem to be a blend of the characteristics of both parents. In 1865 Gregor Mendel found that individual traits are determined by discrete "factors", today known as genes, which are inherited from the parents. Mendel proposed that each trait is determined by a pair of genes. The ideas of Mendel were not appreciated by naturalists until 1900, when three scientists independently confirmed his results. By that time there was strong evidence that cells are basic units of life. Biological stains were developed that highlighted structures within cells, including threated-like chromosomes. Different organisms proved to have different numbers of chromosomes, suggesting that they might carry information specific for each life form.

Chromosomes are structures formed from wrapped DNA. Most cells in the human body have 23 pairs of chromosomes, making a total of 46. Individual sperm and egg cells, however, have just 23 unpaired chromosomes. You received half of your chromosomes from your mother's egg and the other half from your father's sperm cell. A male child receives an X chromosome from his mother and a Y chromosome from his father; females get an X chromosome from each parent. Genes are working subunits of DNA. DNA is a vast chemical information database that carries the complete set of instructions for making all the proteins a cell will ever need. Each gene contains a particular set of instructions, usually coding for a particular protein. Today we believe that only ten percent of DNA is functional, and the rest of it is "garbage". The complete set of 30 000 to 40 000 genes is called a genome.

For most of our genome we receive half of our genes from our father and from our mother. Each half represents shuffled combination of DNA passed down to us from our ancestors. This recombination process makes it difficult to study lines of descent - it creates a genetic mix of everyone who has come before. Fortunately for anthropological geneticists there are parts of the genome that are passed down unshuffled from parent to child. In these segments the genetic code is varied only through occasional mutations - random spelling mistakes, in the long sequence of letters that make up our DNA. When these mutations are passed down through the generations they become markers of descent.

The Y chromosome is sex determining chromosome in humans. It is an unusual segment of the human genome since, apart from two small regions in which pairing and exchange take place with the X chromosome, it is male-specific and haploid, and escapes from recombination. These unique properties of the Y have important consequences for its mutation processes, its genes, and its population genetics: Y chromosomes pass down from father to son largely unchanged, except by the gradual accumulation of mutations. By examining the differences between modern Y chromosomes we can attempt to reconstruct a history of human paternal lineages.

If the Y chromosome traces the male lineage back through history then mitochondrial genome (mt DNA) can be considered its female counterpart. Mitochondrion is small, membrane -bound cellular structure responsible for converting nutrients into the energy-yielding compound adenosine triphosphate (ATP) to fuel the cell's activities. This function, known as respiration, is why the mitochondrion is frequently referred to as the "powerhouse" of the cell. Interestingly, biologists have found that mitochondria have their own DNA (mt DNA) separate from the cell's DNA. In addition, mitochondria can create their own proteins and reproduce to form new mitochondria. This evidence suggests that perhaps mitochondria were once separate living organisms which somehow became incorporated into eukaryotic cell. There are no mitochondria in the head of mature sperm that is way mitochondria are passed down solely from mother to offspring. This maternal inheritance creates a family tree that is not affected by the typical shuffling of genes that occurs between a mother and father.

The greatest history book ever written is the one hidden in our DNA, we hope we find a way to read it.