Decoded: How your facial expressions mirror your mother

Know why your new born's dark eyes resemble your wife or his/her charming smile reminds you of teenaged days?

This resemblance is not pre-determined but happened randomly between two copies of every gene for a given trait - one from mom, the other from dad.

In general, both copies of a gene are switched on or off as an embryo develops into an adult.

The 'switching on' of a gene begins the process of gene expression that ultimately results in the production of a protein.

New research shows that this random phenomenon is far more likely to be found in mature, developed cell types than in their stem cell precursors.

This, in turn, offers an unexpected glimpse of randomness and variability in gene expression.

"This significant amount of flexibility and randomness in gene expression is important for adaptation as a species evolves, but it is unclear how it functions in organisms today," said professor David Spector at New York-based Cold Spring Harbor Laboratory (CSHL).

Occasionally, a cell will arbitrarily begin to use of one copy of a gene over the other.

The activation of only one member of a gene pair is called 'monoallelic gene expression'.

To better understand when 'monoallelic gene expression' is established, Spector and his team collaborated with researchers from the European Molecular Biology Laboratory.

The team used advanced sequencing technology and analysis tools to globally assess allele usage in two different cell types.

They compared embryonic stem cells which can change or 'differentiate' into nearly any type of tissue with cells that had already differentiated into the precursors of neurons.

They found a 5.6-fold increase in the number of monoallelically expressed genes in the differentiated cells.

The team was surprised to find that 8 percent of the monoallelically expressed genes were able to boost their level of expression to compensate for what would otherwise be a shortfall.

"This work raises many important questions like how does the cell know how much of each protein to produce? How much flexibility is there? What is the tipping point toward disease?" noted Spector.