- The study of the mechanisms that modulate gene expression without altering the DNA sequence.
- The whole of an individual's hereditary genetic characteristics.
- An irreversible modification of the DNA code.
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Correct answer: 1.
The study of the mechanisms that modulate gene expression without altering the DNA sequence.
Why?
Genetics is concerned in particular with genes and the DNA sequence. Epigenetics, by contrast, studies rather the way in which certain genes are activated, slowed or silenced, without the text of the DNA being modified.
It can be pictured as a layer of regulation: all the cells of an organism broadly possess the same genetic information, but they do not all use it in the same way. It is these differences in expression that help to produce different forms, functions or behaviours.
What to understand
In the honey bee, the best-known example is the differentiation between queen and worker. A female larva possesses a common genetic potential, but its development depends strongly on its larval feeding and on physiological signals that direct the expression of certain genes. Epigenetics is among the mechanisms involved, even though it does not explain everything on its own.
Another example concerns adult workers. A young bee often becomes first a cleaner, then a nurse bee, then a builder, then a forager. This age-related division of labour is not entirely rigid: depending on the colony's needs, certain workers can resume tasks normally carried out by younger bees. These changes in behaviour may be accompanied by modifications in gene expression.
DNA methylation is an important epigenetic mechanism. It consists of adding small chemical groups to certain parts of the DNA or its molecular environment. This does not change the DNA sequence, but it can influence the reading of certain genes.
Answer 2 describes rather the genotype, that is, the whole of the hereditary genetic information. Answer 3 corresponds more to the idea of a mutation or a lasting alteration of the genetic code, which is not the basic principle of epigenetics.
What to remember
Epigenetics does not change the text of the DNA: it influences the way that text is read and used.
In bees, it helps to understand why genetically close individuals can develop different forms, functions or behaviours according to their feeding, their age and the colony's needs.
Further reading
► Epigenetics
► Epigenetics calls the tune for genetics
► Adaptation of DNA according to role
► Royal jelly: one of the many factors in making a queen