Gene activity can be affected by a specific DNA (Deoxyribonucleic Acid) that does not change its sequence. Epigenesis outlines how genes are expressed differently depending on the necessity of the body or the environment. It can cause genes to change in both positive and negative ways. For example, if a woman does not consume enough carbohydrates during her pregnancy, it may result in the child developing neural tube defects (defects of the brain, or spinal cord). Similarly, if an individual is genetically vulnerable to heart diseases but maintains a healthy diet and does regular physical exercise, the individual is less likely to develop the ailment.
An individual receives two copies of the genes, one of them is from the mother and the other from the father. Usually, both copies are active, but in some cases, only one copy of genes gets activated. The copy depends on the parent of origin, that is, some copies are automatically activated when received from the father or the mother, and this process is known as genome imprinting. For example, the development of Prader Willi Syndrome, which is characterized by intellectual disorders, deficiencies in sexual development, and obesity, has been linked to a lack of genes inherited from the father. It often occurs when two copies of chromosome 15 are passed on from the mother and no copy of chromosome 15 is passed from the father. However, researchers are still attempting to understand how the loss of the mentioned paternal gene results in the Prader Willi Syndrome.
The belief that certain environmental factors influence the expression of specific genes is known as epigenesis. For example, an unhealthy diet, lack of exercise, and exposure to pollutants might trigger the expression of inherited obesity genes.
When the expression of a gene is dependent on its inheritance from a particular parent, it is known as genomic imprinting. It suggests that for the expression of some genes, only one copy is sufficient and it should come from a particular parent. For example, expressions of diseases, for instance, asthma, are inherited from the mother rather than the father.